Serious overheating puzzle

[skipjack27]

I have a Volvo 200hp 1987 model AQAD41A diesel, with a DP290 leg. I am being plagued by a serious overheating problem in which the engine temperature alarms go off and the gauge shows the temperature seriously over the limit. This has happened on 4 separate occasions so far, and there are now some very clear circumstances that accompany every occasion:

1. The overheating ALWAYS occurs somewhere between 5 and 10 minutes after starting the engine and setting off.

2. It doesn't matter whether the engine hasn't been used for weeks, or whether it's just spent an afternoon tearing around the ocean. In other words the preceding state of the engine in terms of its temperature doesn't appear to have any relevance.

3. When the overheating occurs, I turn the engine off and leave it to cool for 15 minutes or so. I can then restart it and it will run perfectly normally - no trace of any overheating. There is thus clearly no blockage of any kind, impeller damage, or pump failure. There's no way that sort of thing could be "cured" by a 15 minute cooling off.

So what is it that can cause sudden, extreme overheating within 10 minutes of less of start-up, but only strikes once in every 3 or 4 start-ups? And, as an apparent problem, completely disappears until the next occasion.

It's worth noting that I've had a lot of work done on the various cooling systems in the course of correcting a different overheating problem in the past, culminating in a through-hull raw water intake that bypasses the original intake from the leg. It's also worth noting that I spent $20k on an engine rebuild between the third and fourth of these overheating incidents. The rebuild was done by a careful and competent mechanic. The prior work on the cooling systems may not have been done so competently.

I'd really appreciate any hints about what might be happening here.

Jeff

 

[tpenfield]

Re: Serious overheating puzzle

I had a season of similar plaguing overheating issues. It turned out to be marine growth/sea weed, etc. intermittently clogging the cooling system.

If you do not have a sea water strainer, then you should probably add one, based on your description of the problem.

 

[PCUK]

Re: Serious overheating puzzle

I wouldn't be so sure there is no blockage! This sounds like something floating around in the cooling system and occasionally causing a blockage. Have you ever had an impeller break and not found all the vanes? This sort of intermittent problem is going to need some serious investigation and I'd start by going right through the cooling system from end to end.

 

[skipjack27]

Re: Serious overheating puzzle

I do have a seawater strainer. And on every occasion on which this has happened, I've removed the cap to the strainer, turned the engine over for a second or two, and always observed a "gusher" of seawater. There has never been anything significant in the strainer. So, the problem certainly isn't coming from the initial seawater intake.

I'm not sure about the blockage idea, either. The impeller has never broken in the time I've had the boat. It's always been intact when replaced. In any event, I find it very difficult to believe that on 4 separate occasions some foreign body - like an impeller vane - has blocked the circulating system on start-up, and then magically completely unblocked on a second start-up 15 minutes later. I guess this scenario is not impossible - but it certainly seems unlikely.

On thinking about the problem, I realise that something must be interfering with the water or coolant circulation. I can't think what else could cause an engine to overheat so suddenly and dramatically. It can't be the thermostats; I put new ones in and the problem still reappeared. But I don't know much about these engines - or engines in general. Could there be some kind of intermittent problem with the pump(s)?

 

[IslandManMitch]

Re: Serious overheating puzzle

I bought a very nice looking V-8 inboard engine with unknown history years ago for about scrap price. I installed it in a Correct Craft ski boat and it ran perfect. After 4 or 5 trips it ran hot. I shut down, let cool and restarted to limp in. It ran fine all the way back to the dock. Over the next 6 months I replaced or checked everything that could cause the exact problem you describe. It turned out to be part of an old impeller floating around inside of the engine block.

 

[O-fishal]

Re: Serious overheating puzzle

could be a sticky thermostat

 

[kmarine]

Re: Serious overheating puzzle

I had a simular issue with zebra muscles. I replaced my hoses with clear tubing temporairily to diagnose where the water flow was restricted. This was not a closed cooling system, I wonder if yours is. Do you have infared temp gauge to see where your hot spot is? Is your temp sender accurate and corosion free?

 

[skipjack27]

Re: Serious overheating puzzle

My diagnosis (couldn't think of anything else) was sticky thermostats. So, I replaced both the raw water and coolant system thermostats. Took them home and couldn't detect any problem in testing them. Sure enough, the problem simply re-surfaced.

I don't have an infrared temp gauge, but a mechanic who used one found that my temp gauge is over-reading by 10 degrees f. The overheating in these incidents, though, far exceeds 10 degrees. More like 40 or 50.

I'm inclining toward the idea that the raw water pump is worn or scored and may be sporadically losing priming. A failure to prime on start-up would certainly lead to rapid overheating. And I have no reason to believe that this pump is any less old than the boat: 24 years.

I wonder if anyone has any comments on this? Could a worn/scored pump lose priming on start-up intermittently?

 

[rovid]

Re: Serious overheating puzzle

i have similar problem on a 90 searay ,one of the 350 engines overheats on high rpm ,noticed the intake line comming from impeller gets hot which means the waterflow is reduced on higher speed ,maybe internal corrosion in outdrive causes exaust fumes to push water away from intake water passage ,so instead of sucking water it sucks fumes thus overheating

 

[skipjack27]

Re: Serious overheating puzzle

i have similar problem on a 90 searay ,one of the 350 engines overheats on high rpm ,noticed the intake line comming from impeller gets hot which means the waterflow is reduced on higher speed ,maybe internal corrosion in outdrive causes exaust fumes to push water away from intake water passage ,so instead of sucking water it sucks fumes thus overheating

Interesting. I guess I'd hope that this is not a problem in my case because I've spent a lot of dough over the last year or so having my outdrive taken back to the workshop and thoroughly overhauled (at - needless to say - considerable expense). I'm still inclined, so far, toward my worn/scored raw water pump chamber theory for my fault - and I wonder whether that might also be a possible explanation for your SeaRay problem?

Does anyone know what symptoms can arise from a worn/scored pump? Can it lose priming intermittently on startup, as in my case? And cause sufficient failure of waterflow at high RPM to cause overheating, as in rovid's case?

Interestingly, I'm not entirely sure that I don't share some of rovid's symptoms, as well as my own. Although I've not yet had an outright overheating warning at high RPM, there have been clear signs that all is not entirely well in that department. At max RPM on my boat, the gauge shows a temp around the max allowed, and the overheating alarm starts to burble a bit (but not actually go off). There is some indication that this happens even at max cruising RPM. In other words, there is a definite suggestion that the system is not coping properly with engine heat at the high end of engine operation.

 

[PCUK]

Re: Serious overheating puzzle

If the pump is badly worn it will not prime on start up. Once it is primed it will run without loss of pressure. So it either works or it doesn't! If there is a wear plate in the bottom of the pump turn it round and also reverse the front plate. Doing this will give you the equivalent of a new pump! I still say you have an intermittent blockage!

 

[skipjack27]

Re: Serious overheating puzzle

Thanks for the comments, PCUK. I'm still waiting for the wretched mechanic to get around to having a look at the pump. There is no reason why I couldn't look at it myself - in fact I unbolted it on one of the early overheating episodes, expecting to find a damaged impeller (it wasn't) - but I doubt that I could make any experienced judgment re the wear or otherwise in relation to possible loss of priming.

If the mechanic finds wear, we'll talk about fixes.

I hope you're wrong about the intermittent blockage. I guess I find that unlikely for two reasons:

1. As I noted before, there has never been (as far as I know) any impeller disintegration since I bought the boat. In any case, wouldn't this be trapped by the filter?

2. I can't reconcile intermittent blockage with the odd pattern of occasional complete failure of the cooling system, combined with perfectly satisfactory operation the rest of the time. In particular, why would an intermittent blockage ALWAYS occur on startup? (well, I suppose that does make sense - if something was going to cause a blockage, it probably would occur on startup. But it's still not clear why allowing the engine to cool for 10 or 15 minutes ALWAYS results in the complete disappearance of the blockage).

I guess I still adhere to my worn pump hypothesis. Will get back when I have some more info.

 

[Lord Farringdon]

Re: Serious overheating puzzle

Thanks for the comments, PCUK. I'm still waiting for the wretched mechanic to get around to having a look at the pump. There is no reason why I couldn't look at it myself - in fact I unbolted it on one of the early overheating episodes, expecting to find a damaged impeller (it wasn't) - but I doubt that I could make any experienced judgment re the wear or otherwise in relation to possible loss of priming.

If the mechanic finds wear, we'll talk about fixes.

I hope you're wrong about the intermittent blockage. I guess I find that unlikely for two reasons:

1. As I noted before, there has never been (as far as I know) any impeller disintegration since I bought the boat. In any case, wouldn't this be trapped by the filter?

2. I can't reconcile intermittent blockage with the odd pattern of occasional complete failure of the cooling system, combined with perfectly satisfactory operation the rest of the time. In particular, why would an intermittent blockage ALWAYS occur on startup? (well, I suppose that does make sense - if something was going to cause a blockage, it probably would occur on startup. But it's still not clear why allowing the engine to cool for 10 or 15 minutes ALWAYS results in the complete disappearance of the blockage).

I guess I still adhere to my worn pump hypothesis. Will get back when I have some more info.

When I first got my Searay 275 with a Volvo KAD300, I had intermittent overheat episodes which turned out to be something rather simple. The impellor was not getting any water. This was because although it is self-priming, it must have a mixture of water and air before it can prime and pump purely water. In my case, whenever I checked the sea water filter, I let air in the system and the water in the intake hose dropped to sea level which happened to be some distance below the impellor. Therefore the impellor was actually dry when I started the engine. This didn't seem to matter as idled out of the marina but as soon as I increased throttle, the temp shot up off scale! What made this stranger was that overheating didn't happen every time. In fact most times it didn't. I surmised later this was because most times (once I got out of the marina) there was a sea of some sort which 'sloshed' water into the impellor in sufficent quantities it managed to prime. Alternatively, rather than slowly raising the throttle (which I do most times because I hate hitting the engine hard when its still getting to operating temp) I may have gunned it and created enough vacumn to suck some water into the impellor and subsequently prime.

The solution was simple. After checking the seawater filter, top it up quickly with fresh water (or seawater) and put the cap back on just as quickly. After start, feel the impellor housing . If its cold your good. If its warm, its not pumping water.

So the problem should only occur if you check the seawater filter but if you find it happening at other times when you haven't touched the seawater filter, then suspect a leaking/cracked (minor) seawater filter cap.

Terry

 

[Lord Farringdon]

Re: Serious overheating puzzle

Thanks for the comments, PCUK. I'm still waiting for the wretched mechanic to get around to having a look at the pump. There is no reason why I couldn't look at it myself - in fact I unbolted it on one of the early overheating episodes, expecting to find a damaged impeller (it wasn't) - but I doubt that I could make any experienced judgment re the wear or otherwise in relation to possible loss of priming.

If the mechanic finds wear, we'll talk about fixes.

I hope you're wrong about the intermittent blockage. I guess I find that unlikely for two reasons:

1. As I noted before, there has never been (as far as I know) any impeller disintegration since I bought the boat. In any case, wouldn't this be trapped by the filter?

2. I can't reconcile intermittent blockage with the odd pattern of occasional complete failure of the cooling system, combined with perfectly satisfactory operation the rest of the time. In particular, why would an intermittent blockage ALWAYS occur on startup? (well, I suppose that does make sense - if something was going to cause a blockage, it probably would occur on startup. But it's still not clear why allowing the engine to cool for 10 or 15 minutes ALWAYS results in the complete disappearance of the blockage).

I guess I still adhere to my worn pump hypothesis. Will get back when I have some more info.

When I first got my Searay 275 with a Volvo KAD300, I had intermittent overheat episodes which turned out to be something rather simple. The impellor was not getting any water. This was because although it is self-priming, it must have a mixture of water and air before it can prime and pump purely water. In my case, whenever I checked the sea water filter, I let air in the system and the water in the intake hose dropped to sea level which happened to be some distance below the impellor. Therefore the impellor was actually dry when I started the engine. This didn't seem to matter as idled out of the marina but as soon as I increased throttle, the temp shot up off scale! What made this stranger was that overheating didn't happen every time. In fact most times it didn't. I surmised later this was because most times (once I got out of the marina) there was a sea of some sort which 'sloshed' water into the impellor in sufficent quantities it managed to prime. Alternatively, rather than slowly raising the throttle (which I do most times because I hate hitting the engine hard when its still getting to operating temp) I may have gunned it and created enough vacumn to suck some water into the impellor and subsequently prime. The solution was simple. After checking the seawater filter, top it up quickly with fresh water and put the cap back on just as quickly. After start, feel the impellor housing . If its cold your good. If its warm, its not pumping water.

So the problem should only occur if check the seawater filter but if you find it happenijg at other times when you have touched the seawater filter, then suspect a leaking seawatyer filter cap.

Terry

 

[skipjack27]

Re: Serious overheating puzzle

Crikey, Lord Farringdon! Your comments on my problem remind me of why I think this forum is so darned helpful.

I suspect you may have nailed my problem. The seawater filter cap on my engine model is something of a "known issue". I once went to a Volvo "engine night" put on by the mechanics in our local dealership, and I recall that they indicated that you needed to be quite careful to ensure the cap sealed in place properly after being removed. Furthermore, I subsequently had quite a bit of trouble with leakage in the cap that manifested as squirting water while under load. Never entirely figured out whether it was poor cap sealing or a crack in the cap. Anyway, replaced the cap and thought everything was fine.

Note also that some time ago I was experiencing overheating problems through the outdrive sucking air somewhere in trying to bring in seawater. So, I had the outdrive intake sealed off and the raw water taken from a through-hull directly below the impeller. This sets up (in a way that didn't previously exist with the conventional outdrive intake) a situation where taking the cap off the filter lets the seawater drop to sea-level (in retrospect, I realise that I should have closed the seawater valve in the bottom of the boat before removing the filter cap - but hate doing that because, on other boats, have had a nasty habit of forgetting to re-open it later.)

On the strength of your comments, I'm going to cancel my request to the mechanic to look at the raw water pump. Instead, I'll close off the intake, remove the filter cap, ensure it's free of dirt and grit, spread some vaseline around the edges, top the water level up with a hose, and then make sure the cap is replaced tightly. Then we'll see how we go.

Thanks again for this information. I'll be sure to get back later on with information about how it turned out.

Jeff

 

[Lord Farringdon]

Re: Serious overheating puzzle

Crikey, Lord Farringdon! Your comments on my problem remind me of why I think this forum is so darned helpful.

I suspect you may have nailed my problem. The seawater filter cap on my engine model is something of a "known issue". I once went to a Volvo "engine night" put on by the mechanics in our local dealership, and I recall that they indicated that you needed to be quite careful to ensure the cap sealed in place properly after being removed. Furthermore, I subsequently had quite a bit of trouble with leakage in the cap that manifested as squirting water while under load. Never entirely figured out whether it was poor cap sealing or a crack in the cap. Anyway, replaced the cap and thought everything was fine.

Note also that some time ago I was experiencing overheating problems through the outdrive sucking air somewhere in trying to bring in seawater. So, I had the outdrive intake sealed off and the raw water taken from a through-hull directly below the impeller. This sets up (in a way that didn't previously exist with the conventional outdrive intake) a situation where taking the cap off the filter lets the seawater drop to sea-level (in retrospect, I realise that I should have closed the seawater valve in the bottom of the boat before removing the filter cap - but hate doing that because, on other boats, have had a nasty habit of forgetting to re-open it later.)

On the strength of your comments, I'm going to cancel my request to the mechanic to look at the raw water pump. Instead, I'll close off the intake, remove the filter cap, ensure it's free of dirt and grit, spread some vaseline around the edges, top the water level up with a hose, and then make sure the cap is replaced tightly. Then we'll see how we go.

Thanks again for this information. I'll be sure to get back later on with information about how it turned out.

Jeff

No worries Jeff. I can see you are looking at things in a logical way and you are right, a blown impellor would leave some traces in the seawater filter. If you find this approach fixes the problem, you may want to replace your impellor sooner than later since it clearly will have been running hot and dry which may have distorted/weakened it. All the best.

PS: don't forget to feel the impellor housing after start.

Terry

 

[skipjack27]

Re: Serious overheating puzzle

Yes, good advice. Irrespective of what the cause eventually turns out to be, the impellor - as you note - is likely to have suffered in some way. So, replacement would make sense as an inexpensive way of avoiding further trouble.

And I will remember to check the temp of the housing after startup.

Jeff

 

[Lord Farringdon]

Re: Serious overheating puzzle

At max RPM on my boat, the gauge shows a temp around the max allowed, and the overheating alarm starts to burble a bit (but not actually go off). There is some indication that this happens even at max cruising RPM. In other words, there is a definite suggestion that the system is not coping properly with engine heat at the high end of engine operation.

Hi Jeff,

I was re-reading your post and noticed the indications you are getting regarding the engine running hot at high rpm. Once again you may be getting the same problems I had. The 'serious overheating' shortly after start is a different problem to the engine generally overheating at cruise rpms. I had both problems and of course assumed originally that all this overheating was linked to the same problem. It was not. Two separate issues with two separate solutions. My experience was that although I may have got out of the marina without an overheating issue, by the time I had run 45 mins at cruise rpm, the temp had climbed to above normal operating temperature and on one occassion exceeded the coolant resovoir cap pressure and started to spew coolant into the bilge. Effectively, i could not run the engine for longer than 45 mins without stopping and allowing it to cooldown for a while. Now, this could be for a number of reasons and as other posters have indicated you may have a blockage from a previous owner impellor disaster or (more likely) your heat exchanger/oil cooler/aftercooler is in need of servicing. I pulled the cooling system apart and found some scaling on the oil cooler and heat exchanger piping. About 5-7percent of the oil cooler passages were blocked which I didn't think it was too much but, it was explained to me that scaling of the piping in these systems acts like an insulator and even though cooling water may be flowing ok, heat transfer is not occuring. I had all the coolers acid bathed and now the engine runs at exactly the right operating temperature and remains there all day long. It was frustrating purchasing this new (to me) boat and having to do all this maintenance but I guess that's why the previous owner was selling it. He could see the bill staring him in the face. As matter of interest, I have seen a number of cases of twin installations where the port engine runs fine but the starboard engine always runs hot. This can be because the starboard heat exchanger and oil coolers are so difficult to get at that they lack regular servicing.

Terry

 

[skipjack27]

Re: Serious overheating puzzle

Mmm. Interesting stuff, Terry. Although the overheating at high RPM has not actually manifested as an overt problem, I've been around boat engines long enough to sniff a potential problem when I see one. My natural inclination is to see the startup and high rpm overheating as stemming from the same cause - but, as you point out, they may not.

People (including me) find coincidences difficult to deal with. The classic example in my boating history was on a previous boat in which I ran to an offshore island, anchored far too close inshore, and ended up having to drag her off the sandbar with both engines in full reverse. You can imagine how much sand was kicked up and inhaled by the raw water system (these were open, raw water cooled, engines). There was quite significant overheating in one engine on the way back and, being a novice at the time, I called the mechanic in the next day to diagnose the problem. He found a damaged impellor and, after hearing my story, had no doubt whatsoever that inhalation of sand at the island had caused the problem.

But...one difficulty. I had noticed the temp gauge on the engine in question rising steadily to uncomfortably high levels on the way TO the island. In other words, the problem was quite clearly already developing on the way to the island, and merely continued to develop on the way back. While it's possible the sand kickup exacerbated things, there is no question but that an overheating problem was developing well before the sand incident. The mechanic, of course, didn't believe me - and I must admit to having trouble believing myself. But there was no question that overheating was occurring before the sand incident.

So, I'm certainly prepared to consider separate origins for my current two overheating situations.

On the basis of your remarks, I think I need to consider the state of the other elements of the cooling system you mention. I've been assuming that these are ok, because I've had a LOT of work done on them over the last year or two - the previous owners having neglected this dreadfully. Nonetheless, that is no guarantee that they are ok. I'll try to sort out the startup overheating problem first, and then look at what might be happening at high rpm.

Re the startup problem: in line with your suggestion, I pulled out the impellor on the sea water pump. The interior of the pump seems to be fine. There is definitely no scoring, and no apparent (to me) wear - although I really have no experience in what to look for. I tried to take photographs, but the position of the pump makes that almost impossible. The cover plate that I removed has clearly suffered obvious scoring in the past and been reversed. The side that now faces in has no sign at all of scoring - and the letters embossed on the surface also make it clear that there is no evident wear at all.

Took the impellor to pump specialists and bought a replacement. I asked them if they could detect any problems with the old impellor and they showed me how much harder and stiffer the old vanes were than the new impellor I was buying. They pointed out that this stiffness can result in vanes being snapped off on startup. So, it's nice to be installing a new impellor - but there is no evidence that the old impellor or wear/scoring in the pump have been responsible for priming problems. I thus continue to incline toward your idea of a loss of priming being related to air in the system.

Anyway, I'll put it all back together again this weekend and see how things go.

Jeff

 

[Lord Farringdon]

Re: Serious overheating puzzle

Hi Jeff,

That was an interesting story about your previous boat and your scrape with a sandbar! They certainly suck up the sand when the inlet gets close enough! When I was conducting due diligence prior to purchasing my current boat, I discovered a suggestion that the vessel had grounded at some stage. It sounded like the owner had literally driven onto the sandbar although the rumours regarding this incident didn't seem to divulge the speed of impact or what damage was done if any. Needless to say, I had my surveyor do a thorough job of checking the hull for signs of previous damage and/or repair and the techs checked the stern leg and transom sheild. Nothing at all was found and while I was never completely satisfied I had nothing to suggest the boat was 'hurt' in any way by this misadventure if indeed any such misadventure actually occured. Then, sometime after purchase I pulled the cooling system apart and 'bingo'. I found traces of iron sand from one of our local sandbanks. So the rumour was true although the absence of damage or repairs suggests it must have been a slow speed grounding. Interestingly, the answer was staring me in the face all the time. The bilge pump had some black marks all around it which I just assumed was from some oily bilge water. However, at some stage after the incident, they must have dropped the inlet pipe to clean out some sand and this resulted in sand in the bilge which, being iron sand, immediately coated itself around the bilge pump housing attracted by the electromagnetic windings of the pump motor. I later found more sand at the deepest part of the bilge. It seems we have to be an Inspector Clouseau sometimes in order to hunt down what happened and in what sequence!

Anyway, its good to hear your pump is in good order and that you have replaced the impellor. You may have noticed that not only were the blades stiffer on the old impellor but also slightly curved from resting in the impellor housing. This 'memory' and stiffness would have had a detrimental effect on the pumping action of the impellor. It's possible the reduced action of the older impellor might be sufficient to create poor priming at start up whereas a new condition impellor may not exhibit this problem. This is a case of one problem ( leak in the system) being masked until another problem (a weak impellor) exposes it!

Solving one problem at a time is a good idea Jeff and I'll be interested to see if a new impellor coupled with some extra dilgence around the seawater filter and cap checking to ensure proper sealing, overcomes your overheating shortly after start problem.

Cheers

Terry