Mercruiser 898 cooling issue

[gregbones777]

I have a mercruiser 898 serial number 4974784. It’s the 305 Chevy V8. Just recently replaced impeller, new 140 thermostat, brand new exhaust manifolds, I did reuse the exhaust elbows but passage were not clogged. Started and ran the engine today and was still running hot just like before. What’s my next option to try and trouble shoot this over heating issue?

 

[Scott Danforth]

Did you measure water flow?

Did you back flush the PS cooler?

 

[alldodge]

Welcome
Thanks for the serial number it helps a bunch

I'm assuming your in fresh water and open cooled, if your in salt let us know

Might have an air leak or things are clogging up.
To check for a air leak, trace the hose coming from the outdrive to the thermostat housing. Get a 6 inch piece or so of clear hose form the hardware store, 1 hose clamp and a double barbed fitting.

Disconnect the hose from the thermostat housing and place the clear hose in between. Run motor in the water and see if you see any bubbles. If you see bubbles then there is a air leak

If no bubbles get a IR temp gun and verify the thermostat housing is getting same temp as the gauge

 

[gregbones777]

Did you measure water flow?

Did you back flush the PS cooler?

Did not measure the water flow and not sure what the PS cooler is. What is it?

 

[Scott Danforth]

Power Steering cooler

If your old impeller was missing bits, they may be plugging the PS cooler

 

[gregbones777]

Welcome
Thanks for the serial number it helps a bunch

I'm assuming your in fresh water and open cooled, if your in salt let us know

Might have an air leak or things are clogging up.
To check for a air leak, trace the hose coming from the outdrive to the thermostat housing. Get a 6 inch piece or so of clear hose form the hardware store, 1 hose clamp and a double barbed fitting.

Disconnect the hose from the thermostat housing and place the clear hose in between. Run motor in the water and see if you see any bubbles. If you see bubbles then there is a air leak

If no bubbles get a IR temp gun and verify the thermostat housing is getting same temp as the gauge

That’s correct no salt water. So I have been monitoring the motor with a ir temp gun. Seems to be running 170-180, The issue that seems to be happening is the exhaust manifold’s are getting hot. Like 170-180 and can’t hold my hand on them for more than 2-3 seconds. That doesn’t seem right to me but I could be wrong.

 

[gregbones777]

Power Steering cooler

If your old impeller was missing bits, they may be plugging the PS cooler

Okay thank you. The old impeller actually didn’t seem to bad. But the old manifolds were packed full of rust bits along with the elbows, hoses, and thermostat housing.

 

[alldodge]

That’s correct no salt water. So I have been monitoring the motor with a ir temp gun. Seems to be running 170-180, The issue that seems to be happening is the exhaust manifold’s are getting hot. Like 170-180 and can’t hold my hand on them for more than 2-3 seconds. That doesn’t seem right to me but I could be wrong.

If your on a hose then those temps are not that much of a concern

If your in the water, then maybe
Normally one side will be warmer then the other because just the way water flows.

 

[gregbones777]

If your on a hose then those temps are not that much of a concern

If your in the water, then maybe
Normally one side will be warmer then the other because just the way water flows.

Okay. I haven’t had it out on the water yet I got it for a good price and I’m restoring it. I just want to make sure I have everything dialed in before getting on the water.

 

[ScottinAZ]

If your on a hose then those temps are not that much of a concern

If your in the water, then maybe
Normally one side will be warmer then the other because just the way water flows.

thats what I was going to say. The hose doesnt provide as much water usually as the lake does, and if there is any "out of level" condition one side will run warmer. 170-180 on a hose would not concern me, but I also would not run it for a LONG time, as the exhaust is running warmer and less water flow to cool the rubber bits. The engine doesnt care one bit about those temps, in an automotive application, that is the sweet spot for operation. Marine engines usually run a bit cooler on the water thanks to the nearly unlimited cold water they can drink.