Mercruiser 470 overheating

[jabo1]

I have a 1979 IB Mercruiser 470 overheating. Head gasket has been replaced twice, thermostat, riser, heat exchanger and temp gauge. Overheating at full throttle. Slowly goes back down at idle. Serial # 5451437. Any suggestions?

 

[Don S]

Re: Mercruiser 470 overheating

When was the last time the impeller in the raw water pump was replaced? Should be about every other year.
Can we assume since you call it an IB (Inboard) that you don't have an outdrive? Cause if you do have an outdrive, the raw water pump impeller is in the outdrive.

 

[jabo1]

Re: Mercruiser 470 overheating

yes, the impeller has been replaced (last fall). We are at a total loss.

 

[Don S]

Re: Mercruiser 470 overheating

Let me guess, it has the 3" diameter heat exchanger, not the 4" correct?

 

[jabo1]

Re: Mercruiser 470 overheating

Yes, it has 3"

 

[Don S]

Re: Mercruiser 470 overheating

In that setup, you need thermostat PN 76270T, NOT the 99155 number. These are Mercruiser numbers.
Are you sure you had the proper stat installed.

 

[jabo1]

Re: Mercruiser 470 overheating

I will find out if correct stat was installed. Are there problems with the 3" heat exchanger?

 

[Don S]

Re: Mercruiser 470 overheating

If you actually used aftermarket, what were their numbers.

 

[jabo1]

Re: Mercruiser 470 overheating

PN 76270T was installed. Do you have any other suggestions?

 

[edrey1969]

Re: Mercruiser 470 overheating

i had the same problum . at slow rpm the water temp. was fine . just after i rev. the motor up to 2000 rpm (+). the motor will get hot . i can lower the rpm the motor will cool down .what i did was take the out drive out . then i got my air comp. i taken off the hose ,off the voltage reg. and blow in in that hose . the one side that go to the out drive . i found some of a impeller stuck in the rubber hose and in the metal hose at the back of the motor " by the gimble bearing". first the hose was twisted just enought to slow the water down . and with the broken impeller in that hose . on the water temp. is good hope this help .

 

[mhardy0000]

Re: Mercruiser 470 overheating

I have a 1981 470 that is overheating. When the engine is not in gear I can run the engine at 2500 rpm's all day and it dosent get above 150 degrees, as soon as I put it in gear and start to get up on plain it overheats to 240. I have changed the Impeller, checked all the hoses and water is running through them fine. Plenty of water coming out of the prop.
I am at a complete loss. Help :confused

 

[badkins50]

Re: Mercruiser 470 overheating

mhardy0000, you might want to go ahead and start a new thread of your own. you are working on one that is over 2 years old and someone elses problem.

 

[mhardy0000]

Re: Mercruiser 470 overheating

thanks batkins will do

 

[jaleistra]

Re: Mercruiser 470 overheating

I have a 1983 Model 470 (4 inch heat exchanger) with no cooling issues up until this year. I think the temp used to max out around 150 to 160, but temp is now maxing out at 190 while running at 3000 to 4000 RPM pulling skiers. Idling engine at 2000 to 3000 RPM will reduce the temp down to 160 oC in 1 to 2 minutes. Anybody know the temp setting of this thermostat? Lower end unit water pump impellor replaced last fall when bellows was replaced. No overheating issue prior to water pump impellor replacement. Could mechanic have installed incorrectly?
Fixes tried to date as follows:
1) Replaced thermostat
2) Replaced temp sender
3) Backflushed voltage regulator on freshwater side
4) Backflushed freshwater side of heat exchanger
5) Confirmed freshwater flow out of heat exchanger exit tube. Not sure how to measure if sufficient flow.
6) Flushed glycol side of heat exchanger
7) Removed and flushed all glycol hoses, but did not remove inlet fitting to glycol pump as I did not have a glycol pump inlet gasket available.
Any recommendations on next steps? Could I have a restriction in glycol passages of exhaust manifold? The only inspections I have not done on the glycol side are removing glycol inlet cover to water pump, removing glycol reservoir & exhaust manifold.

I would appreciate any insights. Thx.