I put this on the cooling board too.

I have been battling with a very illusive overheating problem for moths. I have a brand new 350 HO crate engine, the whole cooling system has been replaced including the radiator.

The truck idle temp is just fine, but when I bring up the RPM to around 2500 or put a load on the engine the temp guage jumps up quickly to 220-240 or so (sending unit in driver side head near front). Finally today we hooked up an analyzer and found that the computer was reading only 180-205 under all conditions (sending unit in Intake manifold). First thougt was bad sending unit or bad guage. Well, no such luck. Tried a different sending unit, same thing...guage read hot. Now here is the kicker....I moved the guage sending unit the the other head and the guage read a little less than the computer!! I tried the spare sending unit and got the same results. The only thing that I can figure now is that my driver side head is running much hotter (too hot) than the passenger side head. What the heck would cause this??!!

Maybe a blockage, but where might it be?

Any ideas would be great. Thanks!!

Mike

 

Maybe a head gasket with the coolant passage not punched out correctly. Intake gasket with the same issue..
Maybe the drivers head has the proper amount of water restriction and the pass head doesn't have enough. The coolant will always take the easiest route.

A vacuum leak would make a cyl (or more than 1 cyl, depending on where it's at) run hotter.

I'd check with GM if that's where you bought it from. May void the warranty if you dig too deep.

 

The wire/line from the sending unit to the gauge isn't laying on/near the header is it? This will cause higher temp reading at the gauge.

Not sure if this is your problem though, but something to check.

 

It's not the wire to the sending unit, I was sure to keep it away from everything.

I'm going to call Pace Parts on Monday and ask them if anyone else has had a problem with the engine like this. Depending on what they say I'm probably going to pull the intake manifold since that is the only major part that I put on. The rest of the engine was already assembled.

Thanks much for the suggestions and ideas.

Mike

 

May not be the problem, but I had a 305 doing the same thing. Passenger side exhaust temps were ~150-200 degrees hotter than the driver side. The block itself was hotter on the passenger side too. Same problem, run the car under any sort of higher load (including AC on) and the temp would just sail up in a matter of seconds.

Turns out the block was cracked across the lifter valley.

 

WOW!! I hope that isn't my problem. Brand new engine and this thing has done this since day 1.

Mike

 

Problem solved!

I replaced the water pump with a used one that we knew was good and now she works like a charm.

The brand new GMB water pump that I put on the engine when I dropped it into the truck, was bad. Don't know yet exactly what was wrong with the pump, but I'm going to tear it down and find out. I guess that's what I get for assuming a new item was good, oh well.

Of course I discovered all of the above after pulling the intake
manifold off and replacing every other part of the cooling system. The good out of this though is now I know the rest of the cooling system won't be failing anytime soon.

FYI, vortech heads use unrestricted gaskets on both front and rear. The gaskets work on either side of the intake manifold, they're identical. This also may be why you can't have a weak water pump. The TBI heads however, use restricted manifold gaskets in the rear.

Thanks a bunch for everyone's help, input, and suggestions!

Mike

 

Hey mad max I had the same problem with my 305 aparently at the factory they over torqued the head bolts and cracked along the base of the bolt holes

 

Maybe its the wrong water pump. I dont know which you have or which you needed, but the reverse rotation pump has a different impeller than the normal one. They are not interchangeable from a cooling standpoint, but either will fit the block fine.