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Discussion Starter #1
I was hoping with a new engine would come a cooler running one but to no avail. I recently installed a 400 that’s been Stroked to a 461. When driving in stop and go traffic the engine, especially at idle is getting hot, like in the 215-225 range (It’s in the 90’s here in Utah btw). Things that have been checked/modified- Radiator (non-a/c was recently rebuilt. Flow Kooler water pump w/new baffle worked down tight onto the impeller. New Kaufman timing cover. Radiator shroud installed and sealed all around it. Water Wetter added to 50/50 mix. New heavy duty fan clutch. Belts checked. System has been burped. Hoses are new and stay to form also have spring in the lower. Timing is ran off manifold at about 14 degrees base. Carb has been jetted and rodded to run rich. When I turn on the heater to full it is dropping about 5 degrees.
Any ideas would be appreciated. I don’t know what to do next?
 

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Wish I could help you, but you seem to have covered alot of the bases. I know it can be frustrating. You mentioned having the radiator rebuilt. Was it the original one?? From what I read, aluminum appears to cool better then the factory copper/brass. Hope you get it figured out, Nicholas.
 

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Discussion Starter #3
It is the original. It was rebuilt by a quality shop that said it was still in great shape. I thought about an aluminum but I’m trying to stick with what appears stock.
 

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Don't assume your gauge is reading correctly. Purchase a laser temp gun at any auto store and shoot the cooling system in a bunch of places and see if it matches the gauge.

Then go from there.
 

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Jim, sorry left that out. This is with an aftermarket I put in to back up the original gauge. The original runs much lower (maybe modded by Pontiac to do so?) I’ve shot it with the gun and it’s accurate. I’m running the 160 t-stat per Butler’s recommendation. The radiator in vs out is only cooling it about 15 degrees. It has the original fan blade as far as I know. It seems to be in good shape.
 

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Jim, sorry left that out. This is with an aftermarket I put in to back up the original gauge. The original runs much lower (maybe modded by Pontiac to do so?) I’ve shot it with the gun and it’s accurate. I’m running the 160 t-stat per Butler’s recommendation. The radiator in vs out is only cooling it about 15 degrees. It has the original fan blade as far as I know. It seems to be in good shape.
I remember on my 66 the fan blade can be put in backwards. There is an IN and OUT stamped on the fan center that's hard to see.
 

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Jim, sorry left that out. This is with an aftermarket I put in to back up the original gauge. The original runs much lower (maybe modded by Pontiac to do so?) I’ve shot it with the gun and it’s accurate. I’m running the 160 t-stat per Butler’s recommendation. The radiator in vs out is only cooling it about 15 degrees. It has the original fan blade as far as I know. It seems to be in good shape.
I remember on my 66 the fan blade can be put in backwards. There is an IN and OUT stamped on the fan center that's hard to see. I don't think mine was a clutch fan though but I could sure feel the air blasting rearwards when I straightened that out.
 

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Discussion Starter #9
The fan is on correct and is pulling air. Maybe it’s just time for a different radiator? I also replaced the exhaust manifolds when I put the engine in with Rare Exhaust and this seemed like it reduced the amount of air outflow area in the engine bay. Could that be a culprit? I’ve heard these engines run hot but I also run into guys that don’t seem to have any issues. Short straw syndrome?
 

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Duke, sorry you are having that problem,...non AC radiator would be a 3 core radiator. The AC is a 4 core as far as I know.

I use a 4 core Radiator with extra wide downtubes. No difference in external appearance to original radiator, except it does not have the stamped “Harrison” on the top.

Go to US Radiator website put in Pontiac and search around. Also call them they are very helpful, and really know the mounts and sizes etc.

That extra cooling from 4 core and larger than stock down tubes adds a bunch of cooling. My 461 runs at 180 has a 160 thermostat.

A couple of little things I drill 3 1/8 holes around thermostat ring to aid the air movement inside, also make sure your fan is half in and half out of the shroud,

and you may want a seven blade Pontiac fan that came on AC cars....much better.

So I would consider upping that Radiator, looks original and that fan as well...that is what the factory did because the condenser dropped all that heat in the engine bay.....let us know how you do.

Oh you will see Jimmy Shine endorsing US Radiator, they are both California shops, he has built a few cars,....and wants performance and original looks....good luck:nerd::nerd::nerd:
 

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And make sure your fan clutch is the “Thermostatic” type....not the centrifigal type.....one runs with great cooling, the other does not.

They look similar just activate on temp.....which you want ....and not on RPM
 

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Dual 16in electric fans with shroud that pull at least 4,000-4,500 cfm. You get all the cooling at idle.

Also its not the worst to run in those temp ranges as long as your boiling the coolant and actually over heating. Higher pressure cap will raise the boiling point of the coolant even more.

Just as a comparison a lot of newer cars dont turn fans on high until 220.
 

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Discussion Starter #13
Thanks you guys for all the thoughts. I think I’ll try the bigger fan first! The radiator is only dropping the temp about 10-15 degrees I think it should be more like 30-40. So something’s a miss.
 

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Agree with the 4 core, but sounds like a fan issue. I would get the a/c style fan. See if it works better if not put it back on eBay. Also I remember reading an article many many years ago about a guy who's had a bad casting and one of the passages was greatly restricted. He had overheating problems since driving it off the lot. It took a complete tear down and inspection to finally resolve. The engine appears to be the only thing you didn't swap out or change. Sounds super frustrating
Good luck.
 

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I solved my cooling problems in my 66 389 tri-power with Evans waterless coolant. I don’t even run a shroud. The highest temp I’ve recorded was 205, that was in the 90’s sitting in my driveway idling. It’s expensive compared to antifreeze but well worth it
 

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I think you've got a lot of good input already but I wanted to add my $0.02. My '68 had similar issues at idle. In my case the problem was air flow. With the hood up it ran cooler or if I revved it to around 2000 rpm and held it the temp would drop. I eventually went to dual electric fans and all is well...even in the Texas heat.

You didn't say if opening the hood or raising the idle speed had any effect. In my experience if the fan is the issue those things would.

The fan's cheaper but I'm thinking four core radiator and I like aluminum.
 

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Discussion Starter #17
I think you've got a lot of good input already but I wanted to add my $0.02. My '68 had similar issues at idle. In my case the problem was air flow. With the hood up it ran cooler or if I revved it to around 2000 rpm and held it the temp would drop. I eventually went to dual electric fans and all is well...even in the Texas heat.

You didn't say if opening the hood or raising the idle speed had any effect. In my experience if the fan is the issue those things would.

The fan's cheaper but I'm thinking four core radiator and I like aluminum.
I’ve tried bumping up the idle while sitting, it didn’t really make a difference. I’ve also tried opening the hood with little change. The only thing that seemed to help was kicking the heater on. The car runs 190 all day regardless of the heat while moving, but as soon as it sits it gets hot. Maybe this engine combo just needs more radiator? I’d like to know if others running a 461 have had issues with the smaller radiator?
 

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Discussion Starter #18
Agree with the 4 core, but sounds like a fan issue. I would get the a/c style fan. See if it works better if not put it back on eBay. Also I remember reading an article many many years ago about a guy who's had a bad casting and one of the passages was greatly restricted. He had overheating problems since driving it off the lot. It took a complete tear down and inspection to finally resolve. The engine appears to be the only thing you didn't swap out or change. Sounds super frustrating
Good luck.
XceedVne (A/C reference?) the engine was recently rebuilt and all passages checked. I removed the original engine and started with a near matching alternate block and heads. But the heating issue migrated to this engine also. During the rebuild I had the radiator gone through and I was told it was still in great shape by a reputable shop. It is the smaller 15” radiator though. It’s shrouded and sealed, has the 18” 7 blade fan, and new clutch. It sits nearly half in and half out of the shroud. But shooting it while operating it’s only dropping the temp 10-15 from top to bottom. I’ve thought about sticking in the Cold Case set up with electric fans but it pains me to change anything on the car that shouldn’t be there.
 

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If it runs 190 while moving I'd still be thinking air flow but if turning on the heater lowers the temp that kinda sounds like you need more radiator.

I hear Ya about changing to something that doesn't look stock but I like to drive mine and don't want to worry about it overheating. I live in East Texas where it gets plenty hot and the dual electric fans and aluminum radiator work for me.
 
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