Volvo Penta diesel overheating problem

[skipjack27]

I've got a 27' cabin cruiser with an inboard Volvo Penta diesel AQAD41A (1987 model) connected to a Volvo duoprop sterndrive.

Ever since I bought it several months ago, there has been a serious and unresolved overheating problem. Max revs are supposed to be around 3800 revs, taking her to a max of 21 knots. On the sea trial on a freezing cold day in midwinter (Perth, Western Australia - but still pretty darned cold), I got her up on the plane and running at 3400 rpm. She overheated at that stage, but I accepted the result, thinking that she had an old engine (I've since learnt that 1400 hours is NOT old for a diesel, and I should have been getting nearer the original 3800 or thereabouts).

Anyway, come the warmer weather, I now find she won't go over 2700 rpm without overheating. This means I get a max of 8.5 knots, and no hope of getting on the plane.

I've called in the local Volvo experts and spent around 7 grand on the problem. First, they completely overhauled the cooling system. This had been badly neglected and definitely needed to be done, but it made no difference: still maxed out at 2700 rpm.

Second, they decided it must be the raw water and/or circulating pumps causing the problem, and completely overhauled those. Again: no difference (but, again, needed to be done, I think).

They are now considering their options, but I am running out of faith in their diagnostic capabilities and would dearly love some wisdom from this forum.

A few possibly pertinent facts:

- she runs very well, provided revs are kept below about 2700 rpm. Stays cool and nice and we've done quite a bit of running around to offshore islands, etc. But once that level is exceeded, there is a very rapid increase in temperature and the overheat alarm sounds very quickly. The mechanics have confirmed with independent instrument checks that the engine is definitely overheating, as the gauge and overheat alarm both separately attest. It's as though something tips over very suddenly when that critical rpm is exceeded. Something happens at 2700 rpm and/or 8.5 knots that tips the engine environment suddenly over from normal operation to severe and rapid overheating.

- the engine was given it's annual maintenance check a few months ago, with no problems.

- some growth is now starting to accumulate on the hull, but nothing that would account for the kind of overheating that has been present since we bought her

- it sort of looks like a stuck thermostat problem, but it couldn't be that simple, could it? Especially given that the thermostat is in the lovely protected environment of half freshwater/half ethylene glycol. On the other hand, it may not have been replaced for 23 years, for all I know.

- the current hypothesis on the part of the Volvo people is that perhaps over the 23 years of her life there have developed problems with the seals in the various joints through which the raw seawater passes from the stern-drive inlets (which I have confirmed to be clear) to the engine. These could be sucking air and impairing the effectiveness of the raw water input to the heat exchanger. They claim this inevitably happens to older boats, and that the cheapest and simplest solution is to abandon the stern drive raw water circuit altogether and to stick a through-hull in the bottom of the engine compartment that feeds sea water directly into the heat exchanger.

Well, maybe: but I'd sure appreciate some words of wisdom from experienced mariners before committing to yet another expensive (and possibly ineffective) repair.

Jeff

 

[triman]

Re: Volvo Penta diesel overheating problem

Jeff, If you can interpret diagrams have a look through

http://www.marinepartseurope.com/en/e-volvo-penta-410-AQAD41A.aspx

Something in there may leap out and say

"That's it!!!"

But I really would have a look at the thermstat

 

[Bondo]

Re: Volvo Penta diesel overheating problem

I've called in the local Volvo experts and spent around 7 grand on the problem. First, they completely overhauled the cooling system.

Ayuh,... Your information is Totally contradictory,...

1st you state This, then go on to say all the things, such as the T-stat have never been replaced....
The heat exchanger might be plugged, etc...

Which is it,..??

 

[Don S]

Re: Volvo Penta diesel overheating problem

Easy enough to check the air leak theory. Put a short piece of clear hose between the water hose going to the raw water pump and the transom shield. Run it and look for air bubbles. There are only a couple of places that could cause the air leak, and they are all cheaper than going to a thruhull fitting.

 

[skipjack27]

Re: Volvo Penta diesel overheating problem

Many thanks for the replies so far. These have been invaluable. More would be appreciated, if anyone is kind enough to offer any other insights. This is a truly extraordinary forum for getting good hints from smart people.

Triman: thanks very much indeed for the link to that site on the AQAD41A. This is a brilliant site! A really terrific visual guide to the engine and its components. I'm going to have to figure out a way to download that information in a way that preserves its structure, in case it disappears one day.

But since I'm not a mechanic, and have only had experience with petrol engine/shaft drives in the past, I'm not too hopeful that anything will leap out and say "That's it". But I'm definitely going to look.

Don S: I think your advice is right-on, and I'm going to take this up tomorrow with the service people. Why should I go to all the trouble and expense of slipping her and having a through-hull put in unless it can be demonstrated this is going to fix the problem. And, as you so clearly point out, the demonstration is very straightforward.

One thing, though: you seem to think that fixing such a leak would be straightforward - or, at least, cheaper than a through-hull fitting. The service people reckon that this would be a good deal more expensive, involving removing the stern drive, taking it back to the workshop, etc, etc. Their view was that the through-hull was a cheaper and simpler option, anyway. Do you have any comments on that?

Bond-o: your comments were rather less helpful, to say the least. e.g., "The heat exchanger might be plugged, etc..." Where did I say that ??? As I DID say, the first thing that was done was to completely overhaul the cooling system.

One of your comments was useful, though: re the thermostat. As I said, it's not impossible that the thermostat hadn't been previously replaced in 23 years (given the state of some of the other bits and pieces), but you remind me that it is essentially impossible that they couldn't have at least looked at it in the 7 grand's worth of work I've had done on it. So, I went to the invoices - and sure enough: I've been charged for a thermostat kit, and so can assume that this is not the problem.


Re the leak hypothesis that Don S commented on: I came across this observation somewhere else in relation to someone else's overheating problem:

"I'm no big expert on Volvo's so take this for what it is worth. We had one in with the same symptoms and what the problem turned out to be was a leak in the suction side of the system between the sea water pump and the pickup. The pivots for the drive were all worn and this caused a swivel joint to open up and allow air into the system. When the boat was not on plane it didn't matter since the leak was under water. Once the boat planed it would suck air and overheat."

I have to say that this has an eerie ring of relevance to my situation. The boat behaves perfectly until I accelerate to around 9-10 knots or so, and then the temperature falls off the cliff - quite suddenly overheats dramatically. On the last sea trial to test their fixes (unsuccessful), the mechanic observed that the postulated leaky bit on the stern drive may stay underwater until she starts to come up on the plane -whereupon it becomes exposed and sucks air all of a sudden.

I'm new to stern drives (and to planing hull launches in general). Just what ARE the hydrodynamics in relation to stern drives and increasing speed? When and how does the top of the stern drive become exposed to the air?

I'd love to hear any comments on this. In the meantime, I might take her out this weekend and hang over the swimboard while my son pushes her up to planing speed. If you never hear from me again, you'll know I overbalanced and fell on the props and they contrarotated me into little bits...

Regards

Jeff

 

[captmello]

Re: Volvo Penta diesel overheating problem

this is a picture of one of the most common air leaks at the outdrive. If your mechanics didn't check this, well...

[/IMG]

this fitting is notorious for rotting out. This is a picture of a fresh water boat fitting. You can check this yourself by pulling off the intake hose on the outdrive. It's an "S" shaped hose that comes off the fitting right below the ujoint (upper) rubber bellows. There is also a gasket below that fitting that could be leaky.

The other point to check which is a little more difficult, is the oring at the bottom of the pivot tube which requires removing the lower gear housing.

Aside from checking the intake fitting for corrosion, I think I would do the clear hose test before tearing into the outdrive. Do you understand what Don S said about that test?

 

[Bondo]

Re: Volvo Penta diesel overheating problem

Bond-o: your comments were rather less helpful, to say the least. e.g., "The heat exchanger might be plugged, etc..." Where did I say that ??? As I DID say, the first thing that was done was to completely overhaul the cooling system.
One of your comments was useful, though: re the thermostat. As I said, it's not impossible that the thermostat hadn't been previously replaced in 23 years (given the state of some of the other bits and pieces), but you remind me that it is essentially impossible that they couldn't have at least looked at it in the 7 grand's worth of work I've had done on it. So, I went to the invoices - and sure enough: I've been charged for a thermostat kit, and so can assume that this is not the problem.

Ayuh,... You said you have an Overheat situation did you Not,..??
You said the cooling system was rebuilt for 7 Grand,+ then continue to whine about alotta "What If's", that should have been covered in what you said was ALREADY done....
Hence my comments....
If you were clear on What was done, I wouldn't be questioning or suggesting things that had ALREADY been done...
No fear though,....
I won't bother you anymore with useless questioning.....
I don't do Volvos anyways,+ Don is the only 1 around here with a Crystal Ball....

 

[skipjack27]

Re: Volvo Penta diesel overheating problem

Thank you, Captmello. Useful info and pic.

And yes, I did understand what Don S said about the test - and was strongly inclined to carry it out before going further.

On reflection, though, I'm now inclined to save time and trouble (summer here will start drawing to a close before long) and just slip her and have the through-hull installed. I've booked the slipyard for Mon, 8 Feb.

I've become convinced, through the exchanges on this forum and the thinking provoked by them, that the problem definitely lies in the pivot section of the stern drive. She behaves perfectly well until I hit 8 or 9 knots or so and her attitude starts to change. Then - bang! - the temp starts to go up very quickly. This suggests that the increasing speed is putting the boat in a position where the top of the stern drive is able to gulp air through a leaky seal in the raw water pipe.

I now recall that I was able to push the throttle to the wall when pushing into strong wind and waves out on the ocean a couple of months ago. No overheating - because, I now realise, the boat was not able to get anywhere near the plane and the stern drive was not being exposed to air.

I should note that this boat is significantly underpowered: a single 200hp diesel pushing a 27' boat that weighs a minimum of 3 ton, and probably more like 4 ton with water, fuel, furniture, and people on board. In my area, the great majority of boats of this size and weight have twins. I'm not fussed about the lack of power, because speed is not that big an issue. Perth is the world's most isolated capital city, whether you are travelling by road, rail, air - or sea. So, there's nowhere much to go other than the very attractive islands 12-20 miles offshore. But I WOULD like to be able to get her up on the plane and enjoy the 17 knots cruising speed that she's supposed to be able to do in reasonable conditions.

Given all the work that has already been done in an effort to resolve the overheating problem, there is really not much left to look at. Yes, there could be problems with cracked or leaking head gaskets, or even engine blocks, letting air in. But this doesn't seem to be consistent with the observed symptoms: specifically, no problem at all at speeds below 8 or 9 knots or so, and sudden overheating after that.

So, my money's on the leaky seals in the stern drive. In any event, I understand that it is fairly normal practice to dispense with the stern drive uptake of raw water and insert a through-hull in ageing boats (vintage 1987, in my case). Just seems like a much more sensible way to go about things, and I guess I'm not clear on why raw water intake is ever done from stern drives. The intakes on the drive certainly seem to be quite a lot more susceptible to blockage than, say, the through-hulls on my previous half-century old timber cruiser. You could accumulate quite a few barnacles, etc, on those without problem - but it doesn't look like it takes too many to block my stern drive. And the position of the intakes on the drive is just perfect for picking up the odd plastic bag...

I guess I feel that:

a. putting in a through-hull is very likely to, at last, solve the problem, and...

b. even if it doesn't, it's money well spent.

How much can it cost, anyway, for crying out loud? Putting in a through-hull is not that big a deal, is it? Sigh. I guess I'm about to find out...

Jeff

 

[captmello]

Re: Volvo Penta diesel overheating problem

Good luck too you!! Let us know how it turns out.

 

[skipjack27]

Re: Volvo Penta diesel overheating problem

Reporting back to the forum on the results of blanking off the leg intake and putting in a through-hull sea water intake in the bottom of the engine compartment. Many thanks indeed for the terrific input from people here: you've been seriously useful in resolving this problem.

SUCCESS at last! Worked brilliantly. Now able to get up on the plane and power along at around 21 knots (which is the rated max for this boat/engine). So, this is something to pass on, perhaps. The seals in the stern drive water intakes do leak after a while, but this may not become apparent until you achieve a certain speed (around 8.5 knots, in my case). The leaky seal(s) were apparently located somewhere around the pivot point, and it wasn't until the attitude and speed of the boat exposed this area of the leg that it started to suck air and rapidly overheat the engine. Note that a critical diagnostic symptom of this problem is the completely normal behaviour up to a certain speed, and then a very sudden and critical overheating.

But the sea trial that confirmed that all was at last well (after a total expenditure of something like $10,000 Australian - close to the $US at current exchange rates) was something of a funny story in itself, and raised a minor, but interesting, problem. See if you can guess the ending...

My wife, the mechanic, the boat, and I (sounds like the title of that rather nasty little art film) set off down the river on a sea-trial to test the effect of the new through-hull intake. Pushed the throttle to the limit and held it there while she wound up to 21 knots. Engine temp stabilised at 88c - optimum. Satisfied, I pushed her round in a steep and long turn to go back without slowing down. She was just coming out of the turn when the engine died completely and wouldn't restart. The mechanic was dumbfounded - it had all the signs of a diesel that had run out of fuel, but a look at the fuel tank showed a quarter-full (we hadn't intended going out for more than about 20 minutes or so). He did everything he could to locate the problem - unbolting everything he could and examining fuel lines, pumps, etc, and we cranked the engine over repeatedly, with no luck.

Clearly, a diesel that has just been running really well with no history of problems (other than the overheating, which was now obviously ok) can only be suffering from a very limited number of defects that could cause it to come to a sudden halt at high speed - fuel starvation, being the most obvious one.

After some extremely exciting sidelights (being blown by a howling easterly onto the only patch of limestone reef in hundreds of kilometres of river shoreline, trying to anchor on hard, smooth mud 80 feet down, calling Sea Rescue to come from miles away, etc), the mechanic and I had to admit complete failure in diagnosing the problem, and had given up to await an ignominious tow home. Whereupon my wife said "Why don't you try it again?"

We did - to humour her and pass the time - and she burst into life (the boat, I mean, not my wife). Still puzzled, we cancelled Sea Rescue and powered off for home, half hoping to replicate the problem in order to get some handle on it. But she ran like a top all the way back.

At some point on the way home, the mechanic had a brain-wave (have you already guessed?): when I put her into that hard turn to port, the quarter-full tank sloshed all the fuel over to port and exposed the tank fuel intake (which is located on the starboard side of the tank) to fresh air. She gulped air, chewed through what remained in the lines in short order (I was running at max rpm, remember), and air-locked the fuel line. And stopped.

I don't know how we got her going again. Was it all the furious fiddling with the fuel system that the mechanic did? Was it the repeated, extended cranking over? Was I lucky I happened to have an expert diesel mechanic on board at the time? Or is there some inbuilt system for dealing with an air-lock? I'm going to raise this question of strategies for dealing with this problem in another thread.

But, for now, Skipjack flies...

 

[HT32BSX115]

Re: Volvo Penta diesel overheating problem

Geez!



I cannot say for your VP diesel, but most diesels have a fairly low pressure fuel transfer ("lift") pump that will move fuel to the fuel filter and then on to the injection pump.

If that pump is failing (they do fail sometimes) then any little "break" in fuel flow will sometimes kill an engine. Also, if there's a fuel screen in the tank that is partially clogged, it will only make it worse.

Next time you roll that boat into an on-plane turn, have a cup of coffee sitting on the deck. ........ see if the liquid in the cup sloshes over the side or stays more or less level in the cup (the boat DOES bank a little like an airplane!!)

I'm not so sure that you would necessarily uncover the fuel pickup at the 1/4 tank level anyway....... (and you should inspect the tank sender too.....1/4 on the gage might NOT be 1/4 in the tank!!)


Regards,


Rick

 

[skipjack27]

Re: Volvo Penta diesel overheating problem

Thanks for those notes, Rick. The fuel tank is quite new and I assume (hope) that the fuel screen is in good shape. I can also definitely confirm the tank contents - my "sender" is a wooden dipstick!

Your note about the lifter is particularly interesting, though. It's probably ok, since we've had no trouble at all with smooth engine running in the 5 months since we bought her (apart from the overheating problem that was the subject of this thread). But I think it would be well worthwhile having this looked at soon.

Regards

Jeff