3.0l Alpha 1 Gen 2 low speed overheat

[Simoniz]

My boat is craned in and out of the water for the summer and winter seasons, so its a bit difficult and expensive to get it on dry land for maintenance at ad hoc times during the summer.

Despite this, Ive neglected to replace the (OEM) raw water impellor for 4 years and now that the boat has recently been put into the lake (freshwater) it seems to have a low speed overheat, with very little water being pumped up to the engine at 800 rpm idle speed. At anything over 1000 rpm it seems OK with the water temp gauge steady on 175 F with pressure felt in the circulating water pump to thermostat hose and the exhaust system checked with an infra red gun shows 50 deg C (130F). Cruising the boat at planing speeds is also good, and when I lean out over the back, the water coming out of the exhaust relief ports is a comfortable hot temperature, about right for hand washing.

Even though I know Ive gone over the recommended interval for replacing the impeller, Im surprised that its gone bad so quickly, but I suppose the vanes have taken a permanent set, and theres enough clearance to allow the water to take the easiest course at idle speed. The guy in this video says he's run his drive for 320 hrs in 7 years on the original impeller, and that he would put a 2 or 3 year old impeller back into the drive and not replace it.

help help help overheating Mecrusier

1998 Merc 5.7 with Alpha one outdrive. The boat overheated on its first use. I changed the impeller, and it overheated again. I took it apart impeller looks good but i am going to replace it again anyway. I don't know where to turn to troubleshoot. I just realized it looks like my motor...

forums.iboats.com

I don't suppose it will get much worse with a bit of running (might even improve as the impeller recovers from sitting for 5 months?) and I propose to use the boat this summer season (20 hrs) before replacing the impeller in the autumn (fall), by not running it at idle for more than a few seconds at a time, and monitoring the temperatures closely. The boat has an exhaust overheat alarm which sounds at 70 deg C (170F), and during normal running, this doesn't go off.

Anyone see any problems with this? Obviously in an ideal world, Id get the boat out and replace the impeller, but to do so would cost me nearly $300 for the lift, and Id like to avoid that expense if I can.

Finally, do impellers have a shelf life sitting in the box in the shop (constant room temp)?

Thanks for any opinions / input!

 

[Bondo]

Anyone see any problems with this? Obviously in an ideal world, Id get the boat out and replace the impeller, but to do so would cost me nearly $300 for the lift, and Id like to avoid that expense if I can.

Ayuh,..... It's yer boat, 'n yer dice to roll,.....

You already know you have a problem, which will get worse, not better,.....

 

[dubs283]

Your boat has a 3.0 L and you have it craned into the water?

I'm guessing it's a fairly small runabout that would fit easily on most trailers. Talk to a friend with a boat trailer you can borrow to load the boat out, maybe?

Agree with Bondo, your boat, your pleasure but the issue is there. Best to get confirmation of the cause rather than pushing it too far

Gen 2 impellers are pretty stout and often exceed recommended replace intervals by many seasons but they can and do fail. 3.0 L cooling system is about as simple as it gets, can only be so many things that are easily investigated for cause

 

[Dubed]

My opinion for what its worth; Replace the impeller (if after troubleshooting that is the determined problem).
The issue will not fix itself and will not get better, only worse till you eventually find yourself stranded or overheat and kill your motor (or both). Its a shame you dont have a trailer or stands to put the boat on and service yourself. You can have a tech do the repair if you arent able to (it would be cheaper than a catastrophic failure).
It seems you are desperately seeking approval to do something that you know you shouldn't. I dont think you will get that here, nor should you.

 

[Simoniz]

Thanks for the replies.

Your boat has a 3.0 L and you have it craned into the water?

Yeah, it's on a large freshwater lake (The Wannsee near Berlin, Germany), which has various moorings areas scattered around it. My boat is in a great spot, easily accessible from where I live, and very sheltered so theres no problem with wake or waves, but theres no slip, so twice a year in April and October they come with a crane and lift the boats out onto blocks and stands where they sit for the winter.

I'm guessing it's a fairly small runabout that would fit easily on most trailers. Talk to a friend with a boat trailer you can borrow to load the boat out, maybe?

Same problem, no slip. I could drive the boat (Bayliner 175) round to somewhere where there is a slip, but then theres the problem that the trailer wont be, and cannot be adjusted to a boat thats in the water. I also only have a small car with no towball, although I guess I could still pull a trailer out, using ropes and the towing eye.

It seems you are desperately seeking approval to do something that you know you shouldn't. I dont think you will get that here, nor should you.

Yes, and Im sorry for that. Obviously no one on here is going to say, 'Yeh, I agree that you've got an overheat problem, but crack on.' Maybe I was hoping someone would say, "Yeah, you know what, its not ideal, but its doubtful that the impeller has disintegrated totally, and since you're still getting g a decent volume of water at all speeds above idle, and you've had a look round and all the indictions are that the engine is staying cool, as long as you're careful not to run it at idle speed, it will probably be OK for this summer till you can get it out of the water and put in a new impeller."

I was thinking about teeing in a pressure gauge so I can keep an eye on the water pressure, just for this summer, or maybe Ill bite the bullet and pay to get the boat pulled out, and I can do the impeller, as I should have done last winter, or the one before that. You live and (hopefully) learn.

 

[dubs283]

Most trailers can be easily adjusted to fit a range of boat lengths. Given how small your boat is you probably wouldn't even need to adjust as long as you use the right size trailer. Bunk trailers are the best, avoid using a roller trailer, they need to be set pretty precisely to fit a boat proper. I use a single axel A-frame trailer to pull boats of your size with great success

Before committing to getting the boat on a trailer it's in your best interest to verify there are no blockages in the cooling system. This includes the supply hose from the transom to the t stat housing and exhaust manifold/elbow. Verifying flow at idle speed is an easy check, specs for volume over time at idle are in the oem manual

 

[Simoniz]

Most trailers can be easily adjusted to fit a range of boat lengths. Given how small your boat is you probably wouldn't even need to adjust as long as you use the right size trailer. Bunk trailers are the best, avoid using a roller trailer, they need to be set pretty precisely to fit a boat proper. I use a single axel A-frame trailer to pull boats of your size with great success

Before committing to getting the boat on a trailer it's in your best interest to verify there are no blockages in the cooling system. This includes the supply hose from the transom to the t stat housing and exhaust manifold/elbow. Verifying flow at idle speed is an easy check, specs for volume over time at idle are in the oem manual

Cheers for the trailer advice; yes if I could get a simple trailer, Im sure it would be OK.

Im confident theres no blockage. The boat was fine when it was winterised, and although theres very little water flow at 800rpm idle, the flow at only 1200 is plenty, and at 3000 like a fire hose.

Occams razor: the impeller has had enough of sitting around at freezing temperatures for the past 4 winters.

 

[JASinIL2006]

Are there no marinas where people have their boats worked on? How do other boat owners do mid-season maintenance or repairs?

I do think it's common for Gen 2 impellers to last longer than 4 years; I just serviced my water pump and the impeller is at least 5 years old and it looked fine. (I replaced it anyway because I'd already purchased a kit.)

There is a lot of difference between a 4 year old impeller that's working fine and one that isn't keeping the engine cool at idle. I guess you have to balance the cost of having the boat pulled so you can replace the impeller vs. the cost of possible having to repair/replace an overheated engine.

 

[Simoniz]

Are there no marinas where people have their boats worked on? How do other boat owners do mid-season maintenance or repairs?

I do think it's common for Gen 2 impellers to last longer than 4 years; I just serviced my water pump and the impeller is at least 5 years old and it looked fine. (I replaced it anyway because I'd already purchased a kit.)

There is a lot of difference between a 4 year old impeller that's working fine and one that isn't keeping the engine cool at idle. I guess you have to balance the cost of having the boat pulled so you can replace the impeller vs. the cost of possible having to repair/replace an overheated engine.

Well, as I said, I could have the boat craned out, but Id be looking at nearly 300USD. I know thats much cheaper than a replacement engine, but as I also say, Im not convinced that with a bit of careful handling it would come to that.

It is weird. A few years ago I did an impeller replacement which also wasn't pumping much water at idle. I expected the old one to be shot, but when I disassembled the pump, everything looked fine, apart from the impeller blades having a set to them.

 

[Lou C]

Sometimes the wear plate can get scored from use or sucking up sand in shallow water. The impeller can look good but the scored wear plate stops it from pumping 100%. I go about 3 years on impellers unless i see a need to change is sooner. The OMC Cobra design makes it very easy to change, remove a plastic cover on the tail end of the upper gear housing & its right there 3 bolts no need to remove the lower gear housing.

 

[Simoniz]

Sometimes the wear plate can get scored from use or sucking up sand in shallow water. The impeller can look good but the scored wear plate stops it from pumping 100%. I go about 3 years on impellers unless i see a need to change is sooner. The OMC Cobra design makes it very easy to change, remove a plastic cover on the tail end of the upper gear housing & its right there 3 bolts no need to remove the lower gear housing.

Well I did suck up a bit of sand but that wasn't last year, it was the year before, but of course its going to bring the pump components that bit closer to the end of their life.

I honestly don't know why I didn't change the damned thing when it was out of the water. I even grabbed a box from a shelf in my garage which I thought contained an oil filter and took it to the boat. When I got there, it was an impeller - the universe trying to tell me something.

Yes you have to wonder about the wisdom of a design where a consumable part which needs changing at regular intervals is buried deep in the works, and inaccessible when the boat is in the water. I suppose we should be grateful Mercruiser didn't put the oil filter somewhere inside the sump.

 

[Stinnett21]

1000 rpms is idle speed through no wakes on my boat, maybe even 1200 if no one yells at me. If you say it's ok at 1000 maybe you can nurse it through. How much can you get by with at 1000 in your situation? How long do you have to idle at 800 to get to your slip? If you can get to the slip fairly quickly go to neutral, rev it up into the cooling range and get the needle to drop before shut down. Look I know I'll get crucified for even saying this but I feel for your situation. If you boat as long as I have the list of stupid things done tends to mount.

 

[Lou C]

one of OMCs better ideas:

 

[Lou C]

Well I did suck up a bit of sand but that wasn't last year, it was the year before, but of course its going to bring the pump components that bit closer to the end of their life.

I honestly don't know why I didn't change the damned thing when it was out of the water. I even grabbed a box from a shelf in my garage which I thought contained an oil filter and took it to the boat. When I got there, it was an impeller - the universe trying to tell me something.

Yes you have to wonder about the wisdom of a design where a consumable part which needs changing at regular intervals is buried deep in the works, and inaccessible when the boat is in the water. I suppose we should be grateful Mercruiser didn't put the oil filter somewhere inside the sump.

Well where the oil filter was located was originally determined by General Motors, when they designed these engines a LONG LONG time ago! The 3.0 4 cyl is very easy but on any of the V6s or V8s, it is way back up against the flywheel housing on the port side rear of the engine. Some boats you can get at it OK, others it is torture. Mine isn't too bad I have to pull out 1/2 of the rear seat and wood supports & slide the battery back to get at it.

But after 20 years of the gymastics needed to get at this, I am installing this in the fall:

age will do that to you lol.

 

[Simoniz]

1000 rpms is idle speed through no wakes on my boat, maybe even 1200 if no one yells at me. If you say it's ok at 1000 maybe you can nurse it through. How much can you get by with at 1000 in your situation? How long do you have to idle at 800 to get to your slip? If you can get to the slip fairly quickly go to neutral, rev it up into the cooling range and get the needle to drop before shut down. Look I know I'll get crucified for even saying this but I feel for your situation. If you boat as long as I have the list of stupid things done tends to mount.

Cheers. Yes I can motor round at 1200 rpm to get to the area of my slip, and I can chop the engine and coast in the last few feet, using a boat hook to pull the boat into position. Same coming out, I can position the boat in the lane, pointing the right way, start up and motor off (obvs not so much of a problem there as Im starting with a cold engine and exhaust).

When they put the boat in the water last week, I took it for a spin to see how it was and to burn off the winterisation oil. I didn't even notice the problem until I stopped the boat to let it idle while I tried to sort out my gps which wasn't tracking satellites properly. The temp gauge went above the usual 175F to around 185 so I shut it down and had a look round with the heat gun I had taken with me. I realise that im only measuring the temperature of the outside of the manifold there, and that if it didnt have much water in it, then the inner walls would probably have been much hotter. Starting up again and introducing a load of cold water probably isn't ideal, but as I say, I reckon now Im aware of the problem, I can avoid idling the boat completely, or at least limit it to 5 seconds or so.

 

[Simoniz]

Well where the oil filter was located was originally determined by General Motors, when they designed these engines a LONG LONG time ago! The 3.0 4 cyl is very easy but on any of the V6s or V8s, it is way back up against the flywheel housing on the port side rear of the engine. Some boats you can get at it OK, others it is torture. Mine isn't too bad I have to pull out 1/2 of the rear seat and wood supports & slide the battery back to get at it.
View attachment 379446
But after 20 years of the gymastics needed to get at this, I am installing this in the fall:
View attachment 379447
age will do that to you lol.

Much more civilised!

 

[Lou C]

Engine accessibility is one of the reasons why I wouldn't buy most of the newer I/O designs. They appear to be designed by mechanical sadists who hate mechanics. A relative has a 2020 Chapparal with the new style Mercruiser 4.5 which is really a very nice running engine but to get at anything except the water drain, oil filter/fill, and drive oil bottle, would be really tough. I blame the boat companies not Merc or Volvo, there is no reason why it has to be that way. On this boat if you had to pull the starter, or power steering actuator (both jobs I've done on my old one) you'd have to pull the engine.

 

[Dubed]

My 3.7 is very easy to access everything (which is good because you spend a bit of time working on these motors)
Remote oil filter is awesome.

 

[Lou C]

Old tech is good. You just have to understand it isn't a perpetual motion machine. I'll take points & condenser & a 4bb carb, with its drawbacks, vs old throttle body and EFI systems. Merc and Volvo have nasty habit of making key parts for those, NLA. And then, you are SOL....

 

[Dubed]

Old tech is good. You just have to understand it isn't a perpetual motion machine. I'll take points & condenser & a 4bb carb, with its drawbacks, vs old throttle body and EFI systems. Merc and Volvo have nasty habit of making key parts for those, NLA. And then, you are SOL....

Agreed.