[formula400guy]

I just had my original 400 rebuilt 30 over and a midsize Lunati cam. My engine is running at 240 degrees and when I am not moving it is running at 250 .degrees I put in a 190 degree thermostat but it didn't help. I have a recored 3 core radiator with a new stock water pump.

Thoughts on what this might be. The motor didn't do this before the rebuild.

Thanks in advance ,

Keith

[FrankieT/A]

What are you using for a fan ? Clutch? Mechanical or electric?

[formula400guy]

same stock mechanical fan .

[unruhjonny]

I recently read about how remanufactured water pumps often don't have the impeller in the correct spot;

First, did you reinstall the collars and the pump divider?

Second, did you buy a replacement water pump?

If yes on the first, great (some people skip parts);
If yes on the second part, you might need to verify how far the impeller is from the divider...

[formula400guy]

jI ust bought a stock replacement water pump.

[unruhjonny]

Originally Posted by formula400guy

jI ust bought a stock replacement water pump.

That was my guess.

Nnot to be a downer, but that might be your problem right there.

You might want to pull the water pump and plate off, and check the clearance between the impeller fins and the divider.

Hopefully someone more knowledgeable than me can chime in.

[formula400guy]

Thanks one person told me to get a high performance water pump from Ames.. what doesn't make sense it that when I am driving it cools to 235 but when I stop it goes to 250 plus. how would that be a water pump issue. not an air flow issue ?

[unruhjonny]

as I have read it, the bulk of the aftermarket water pumps don't have as tight a clearance as the OEM stuff did;
This reduces flow through the waterpump, and prevents proper cooling to occur...

[george kujanski]

Go to the top of the heating/cooling forum. There is a sticky there called "chalk one up for the cast impeller." You don't need to read the whole thing, the first few pages will tell you what to look for. basically, the plate needs to be as close as possible to the edges of the impeller vanes.

George

[formula400guy]

Thank you .. ill look now.. .

[judgeman6970]

You put a 190 stat in to "try to make it run cooler"? What were you running? No need to run more than a 180 stat. Also, whats your fuel mixture and/or timing? Lots of things may be different after your rebuild, not just your water pump. Fyi, if it was me, I wouldn't run my new engine at those temps for very long....

[formula400guy]

I was running a 160 which meant it was always open and never got the radiator to cool it.. I have to run 10 % ethanol here in Ma that is all they have.. I run 91 octane . I just ordered a high flow water pump from ames and their heavy duty 180 Degree thermostat . I'll see how that works out.

Keith

[Pepi]

Reading that this is happening just after a rebuild, 2 things come to mind. 1) Did the temp sensor get replaced, if so did an original GM one go in, the aftermarket ones always show hotter. 2) have you verified temps with an IR gun?

[formula400guy]

yes I replaced the temp sensor and did use an IR to check the temp . it was the same as the gauge. Thanks

Keith

[Pepi]

Ok, the aftermarket ones are known to give high readings, that was why I asked.

[formula400guy]

I purchased a high flow water pump and backing plate from Ames but was able to fix my overheating problem by getting all the air out of my cooling system. I painted the water pump already so I cant return it. I will sell both items for a little less than I paid for them. plus shipping..

[70GS455]

Did you have any overheating issues before the rebuild? Was it a stock engine?

My thoughts are that if it was a stock OEM, long-duration (at the seat) cam, compared to the new modern cam with shorter seat timing, the later exh valve opening now keeps hot exhaust gases in the cylinder longer, and heating up the water more, as opposed to letting those hot exhaust gases go out the manifolds like before.

Also a new engine will have more friction until it's broken in

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