Another 470 overheating

[jakeb]

79 Mercruiser 470 with the 3 inch heat exchanger getting hot when under a load.

It will sit all day at 140 degrees at any rpm when its hooked to the hose in my driveway, but under a load out on the water it gets hot - 200 plus until I shut her down.

What I have done so far:
New impellor installed, new t-stat, checked the exhaust riser-unrestricted.
Compression check is consistant throughout all cylinders.

It seems like the 4 inch heat exchanger is a popular upgrade but I would like to test some more things before dropping a few hundred on a 4 inch exchanger.

I am thinking about building my own heat exchanger which I have done on another custom boat that worked great.

What else should I do before upgrading the heat exchanger?
It seems like I have another problem if its getting this hot.

I have been reading a lot of posts to learn as much as I can but cant figure it out.

Thanks everyone,

Jake
Oakley CA

 

[achris]

Re: Another 470 overheating

Overheating can have many sources, often with more than one issue generating the problem. Check the following items...

1. Impeller and housing (in the leg).
2. Clogged heat exchanger.
3. Distorted water pocket cover (in the bottom of the top half of the leg).
4. Ignition timing to advanced.
5. Engine overloaded.
6. Any restiction in the cooling system.

Chris.............

 

[jerryjerry05]

Re: Another 470 overheating

Those 3" exchangers can be a problem.BUT!!!! more than likely if the riser is original it's your problem.They only last 15-20 years if you have a 79 then you've been lucky.Them may look like they are ok but when you go past idle the riser can't pass enough water to cool the engine.
I have worked on hundreds of these and the owners all say the riser LOOKS good but as soon as I replaced it the problem went away.
Do you run in fresh or salt? On an outside chance if it's salt them the anodes probably haven't ever been changed.Then the heat tubes could be corrode.But not very likely.Have you ever changed the anti-freeze? It can break down too.But not very likely. Change the riser.I bet your problem goes away.Jerry

 

[jakeb]

Re: Another 470 overheating

Update:
It was the timing. Its such an easy check I should have done it first but I dont own a timing light, so I just borrowed one and what a difference.
It was probably running about 25 degrees retarded.

Runs great now and the temp while cruising is around 160!

Thanks for the help guys.

jake

 

[ne7800]

Re: Another 470 overheating

cool glad you solved the problem, i like to here about goodrunning 470's it make me feel better about mine lmao

 

[chiefalen]

Re: Another 470 overheating

At least he gave us some closure.

Told us it's fixed, and how he fixed it.

 

[TJEli]

Re: Another 470 overheating

I am surprised it even ran being retarded 25 degrees. I bet it runs a lot better now!

-Eli