86 4.3 liter mercrusier continues to overheat

[fwas]

I currently own a 1986 regal boat with twin Mercruiser 4.3, I recently replaced one of my engines, but since then the new engines continues to overheat, I have replaced the lower unit impeller pump, engine water pump, have cleaned out the t-stat housing assembly, manifold risers, and removed the thermostat. At idle the engine runs between 200 and 240 degrees once i run up the rpms to 2200 it tends to cool off between 180 and 220, does anybody have any insight on this. <br /><br />Just a little insight; the other engine runs fine and doesn't have a thermostat <br /><br />Thanks

 

[Stanp]

Re: 86 4.3 liter mercrusier continues to overheat

Did you re-use the old manifold and risers? There is a breakin period of up to 20 hrs for new engines and they typically run hot- not over 200 degrees however. I put money on old riser or manifolds not being able to exchange heat effectively anymore. The other engine where you took the thermo out. Why did you do that? cause it too is running hot? maybe both engines need manifolds and risers. Then, maybe you can put the thermostats back in both engines. Just some thoughts. Had same symtoms on a 4.3 OMC. New manifolds, at $300.00 a peice, new thermo, and impeler and we're good to go. Merc's should be less expensive.

 

[Fouled Plug]

Re: 86 4.3 liter mercrusier continues to overheat

Are the engines fresh or raw water cooled? If fresh, could be a heat exchanger is partially plugged.

 

[fwas]

Re: 86 4.3 liter mercrusier continues to overheat

Stanp:<br />Actually the other engine runs fine I just removed the thermostat to see what would happen, it actually runs cooler even at high RPMS, considering it had that effect I decided to make both engines thermostatless, however, On engine #2 I replaced the old motor because two of the cylinders where bored out beyond sixty, and loosing compression in one of them, I purchased a long block and transferred all external parts to the new engine, I had the risers and thermostat housing dipped in watered down muratic acid, so they are very clean now.<br /><br />Fouled Plug <br />The engines use raw water cooling,

 

[Stanp]

Re: 86 4.3 liter mercrusier continues to overheat

MAybe someone with more knowledge on the subject could coment on this, but there is a good reason to run your engines with thermostats. Also, I don't have a merc but on my 4.3 omc there is an oil cooler that is raw water cooled before the raw water enters the thermostat housing. A partially clogged oil cooler could be the problem as well, but I don't know if merc is equiped the same way. How is the flow of raw water in the new engine compared to the other engine? If your getting plenty of water flowing thru the new engine, there is probable no clog and the impeler is functioning properly. This points me back to the manifolds not cooling effectively. If flow is less than the other engine, re check the impeler and check for clogs. Temp guage could be acting funny too. Can you put your hand on the manifolds without them burning? Manifolds should be warn to the touch but not so hot that it burns.

 

[mobiletech]

Re: 86 4.3 liter mercrusier continues to overheat

Stanp may be on to something. I have a cobia with a 4.3 and just got my overheating problem fixed. My boat mech and myself did everything we knew to do. Checked the flow in and out of everything. Found that the raw water pump had pumped stuff through it to a screen at the powersteering cooler and on mine at high rpms it would over heat.. The way we found it was tried to back flush system from t/stat housing to raw water pump and found that it was stopped up. Took the air hose and blew all kinds of stuff out of it. fortunately my raw water pump is belt driven and easy to get to. Start checking flow on stuff hose by hose.

 

[fwas]

Re: 86 4.3 liter mercrusier continues to overheat

Stanp; I will follow up on that temp guage, I am able to reach the temps sensor from the t-stat housing on the intake manifold and you are right it feels like it has allot of build up on it, i will try that to see what happen<br /> <br />Mobiletech did you reverse the flow of water from the hose that goes to the circulating engine pump, from the lower unit pump or from the hoses that come from the t-stat housing, thanks