Engine overheats

[william haynes]

I have a Mercruiser 3.0 liter in my searay with standard cooling. Boat has been setting for quite a few years and I am in the process of getting it running again. It ran just fine the last time I ran it but it is getting hot now when I run it fast. I have twin engines and have no problem with the other engine. I installed a new impeller in the lower unit and it runs just fine at slow speed. Ran the boat about 35 miles an hour and right away it started heating up. I checked the thermostat when I got home and it is opening up at 140 degrees so I am ok there. Any ideas would sure be appreciated. Thanks. Bill

 

[Howard Sterndrive]

Re: Engine overheats

sounds like an impeller housing sucking exhaust gases. You might try resealing the impeller housing again. somewhat common issue on a Gen 2 Alpha One.
could also be a rotten water hose in the gimbal area

 

[william haynes]

Re: Engine overheats

sounds like an impeller housing sucking exhaust gases. You might try resealing the impeller housing again. somewhat common issue on a Gen 2 Alpha One.
could also be a rotten water hose in the gimbal area

There is no sealing that I know of when an impeller is installed other than the rubber ring that slides down the drive shaft and goes on top of the impeller housing. I have installed impellers on numerous outboards and I/0's and have never had any sealing problems. Are we talking about the same thing? I was wondering if the exhaust manifold needs to be rodded out. Thanks for the quick reply. Bill

 

[Bondo]

Re: Engine overheats

There is no sealing that I know of when an impeller is installed other than the rubber ring that slides down the drive shaft and goes on top of the impeller housing. I have installed impellers on numerous outboards and I/0's and have never had any sealing problems. Are we talking about the same thing? I was wondering if the exhaust manifold needs to be rodded out. Thanks for the quick reply. Bill

Ayuh,.... What Vintage are these 3.0ls,..??

Which drives are mounted behind these 3.0ls,..??

Are ya a saltwater boater, or sweetwater boater,..??

Btw,.... The pump body has to be Sealed to the pump base ya know....

 

[william haynes]

Re: Engine overheats

Both engines are 1987 3.o ltr and have been used in the ocean and fresh water. You are absolutely right about the pump body has to be sealed to the base. I think I might have found my problem. Before I took the boat to the lake I added a can of sea foam to the oil and I think it might have thinned the oil oil out too much. I removed the old oil today and put in fresh oil and oil filter. Right now I am in the process of replacing all the bellows and the shift cable. Thanks for the fast response my friend. Bill

 

[Bondo]

Re: Engine overheats

Both engines are 1987 3.o ltr and have been used in the ocean and fresh water. You are absolutely right about the pump body has to be sealed to the base. I think I might have found my problem. Before I took the boat to the lake I added a can of sea foam to the oil and I think it might have thinned the oil oil out too much. I removed the old oil today and put in fresh oil and oil filter. Right now I am in the process of replacing all the bellows and the shift cable. Thanks for the fast response my friend. Bill

Ayuh,... Pull the Risers, off the manifolds, 'n check that the water passages aren't plugged with rust....

 

[jtracc]

Re: Engine overheats

seafoam to the oil? never used it oil always in a tank of fuel.

 

[LorenHaus]

Re: Engine overheats

Lets keep it simple. Narrow it down to engine restriction or drive water problem first. Not sure if this is in your driveway or at a marina. I would grab 2 pieces of hose to extend your inlet water hose. Swap the cooling water hoses to the other engine, so your port outdrive cools the starboard engine, and the starboard drive cools the port engine. If the engine that NORMALLY runs cooler now runs hotter when doing the lake test, then you know you need to pop a drive open and replace the impeller and gaskets for the housing. Just an easier way to check while in the water. Takes a whopping 5 minutes to add some hose extensions and switch them from engine to engine. Just make sure they are both running otherwise you will starve one engine of cooling water.

 

[Don S]

Re: Engine overheats

And if all else fails (and if you come back) read this Merc service bulletin. It may be older than your drive, but the information is the same.

View attachment 82_04 water pump output test.pdf