[ScoTFrenzel]

Here's one that I would try.

Use an infrared thermometer on the upper AND lower radiator hoses.
There better be at least a 25* drop across the radiator.

That will tell you where to look for the problem.

[ScoTFrenzel]

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Other people think it is voodoo, and continue eating heavy meat diets, dairy products, diet sodas, and sugar....... and stay sick.

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Remember, you are responsible for you,
and the medical industry is there to treat symptoms with drugs and milk all your money.

Think not? Wait until you are totally broke and see how much care you get then.

You have nothing to lose but a good life.

[Arrowhead]

Originally Posted by ScoTFrenzel

When the engine is cold, I would remove the radiator cap and squeeze that lower hose to see if it is collapsing. It better have a spring inside it. IF not, make one from coat hanger wrapped around a broom handle.

Dang!!!! Now theres some redneck engineering!!!! I love it. I think I'm gonna havta steal that one.

[T-bucket23]

Originally Posted by ScoTFrenzel

Pressure has everything to do with cooling, especially a SBC.
SBC are notorious for nucleate boiling= steam pockets forming next to the combustion chamber. Once steam begins to form overheating gets worse. That is the reason that SBC had the temp gauge at the front of the left head. The LT1 reverse cooling was an attempt to stop it.
System pressure reduces nucleate boiling.
High flow water pump pressure reduces nucleate boiling. A high flow pump can add several pounds of pressure at the chambers.
Evans Coolant (367* boiling point) reduces it.

***********
Post #1 that the gauge hits 290* is wierd. 50/50 coolant can't exceed 257* with a 16# cap.

When the engine is cold, I would remove the radiator cap and squeeze that lower hose to see if it is collapsing. It better have a spring inside it. IF not, make one from coat hanger wrapped around a broom handle.

***********
Thank you to all military personell for serving.

MIA/POW and PH, you are not forgotten. I wasn't there (VN) but I still care.

former cooling system engineer

Your saying the same this I am just from a different perspective. I dont want to get into a pissing contest. As for temperature the head metal or intake metal has no temperature limit and once the coolant starts to boil it doesnt cool any more so the metal keeps getting hotter, this is why the gauge will continue to rise and usually does so rather quickly.

Chet

[bluesman2333]

I didn't want to get into any head butting either. That's why I didn't say any more on that particular subject. I will tell you that without pressure, you will not have cooling. Looking at it from any perspective, that is what it boils down to. (hehe now THAT'S a pun!)

Whatever the source, when the problem is uncovered, it will be screaming "Why didn't you see this sooner!" At least that's how it is here.

[cmk59]

Post #1 that the gauge hits 290* is wierd. 50/50 coolant can't exceed 257* with a 16# cap.

Who said anything about 290? I said 220, and the gauge only goes to 260...

[ScoTFrenzel]

Originally Posted by Arrowhead

Dang!!!! Now theres some redneck engineering!!!! I love it. I think I'm gonna havta steal that one.

OH ya, and that is a wire coat hanger, not plastic. LOL
************************************************** ******
Hey all you guys, we're not pissin, we're discussin and trying to learn a new angle on things that maybe we haven't ever seen before.
And maybe I'll find out that I have been wrong about somethin.

Thanks for all the input. Cooling is my second favorite subject (for hot rods that is).

[ScoTFrenzel]

Originally Posted by cmk59

Who said anything about 290? I said 220, and the gauge only goes to 260...

From post # 1,,,,,, guess you did.

quote
BUT, she has a cooling problem from Aitch Eee Double Hockey Sticks I can't figure out or fix. For 2 years, the idiot light came on intermittently, but could find no trouble. Added an Auto Meter gauge with probe inserted in lower center of radiator, but this showed actual NUMBERS that freaked me out...well over 290 degrees, w/o the A/C on! quote

no problem

[alittle1]

Chuck,

Sat here and read all the posts and absorbed them for their value.

In my opinion, I would say that you have a cracked head on this engine more so, than a blown gasket. The other possibility is, are you sure that the thermostat is installed correctly and opening properly. I would suggest installing a stainless steel "NO FAIL" thermostat, instead of the run-of-the-mill brass type.
I would run with a 180 or 192 thermostat, rather than the 160 because the higher 180+ will keep the coolant in the radiator allowing it to cool down more.

Have you checked out http://www.crankshaftcoalition.com/w...cooling_system

[malc]

"rather than the 160 because the higher 180+ will keep the coolant in the radiator allowing it to cool down more"

I´ve never got on well with statements like that about the cooling system.
If the cooling system is a closed circuit staying in the rad longer will also mean it stays in the motor longer, absorbing more heat.
Surely the speed of the coolant flow is determined by the water pump, to speed up or slow down the coolant you´d have to swap pump pullies.

The thermostat controls the opening of the cooling circuit allowing coolant to flow solely for the reason of getting the motor to operating temperatures quicker.
It then opens and closes as needed to keep the motor in the heat range chosen.

[ScoTFrenzel]

Originally Posted by malc

"rather than the 160 because the higher 180+ will keep the coolant in the radiator allowing it to cool down more"

I´ve never got on well with statements like that about the cooling system.
If the cooling system is a closed circuit staying in the rad longer will also mean it stays in the motor longer, absorbing more heat.
Surely the speed of the coolant flow is determined by the water pump, to speed up or slow down the coolant you´d have to swap pump pullies.

The thermostat controls the opening of the cooling circuit allowing coolant to flow solely for the reason of getting the motor to operating temperatures quicker.
It then opens and closes as needed to keep the motor in the heat range chosen.

AGREE, you are correct.
I might add,
A closed thermostat gets the engine up to operating temperature quicker than an engine without a thermostat which would be circulating the water continuously.

Thermostats control the MINIMUM operating temperature of the system.

The most valuable tool for cooling system diagnosis is an infared thermometer. Make sure you have at least a 25* drop from inlet to outlet of the radiator in every condition.

And if I might comment about the original statement of keeping the coolant in the radiator longer to let it cool more.......
If that were logical, then why would we turn the water pump faster as the rpm increased? Wouldn't we want to keep it slow to cool better?

[Holder350]

Originally Posted by alittle1

I would run with a 180 or 192 thermostat, rather than the 160 because the higher 180+ will keep the coolant in the radiator allowing it to cool down more.

Ok I have had problems with motors WITHOUT a thermostat in them (must install a restrictor) because it lets the coolant flow to fast thru the rad and not dissipate its heat into the air.

Heat dissipation from hot metal to water happens fast. (dunking a hot item into water)

however dissipating heat from water to metal (without any evaporation) is not nearly as fast....even then the heat has to be passed from the metal into the air.

So I said all that to say all this --

Installing a different temp thermostat will NOT keep the water in the rad longer. The two thermostats have the same sized opening in them, thus after the motor hits the correct temp where the thermostat opens the water will not flow thru either any faster.

[malc]

Ok I have had problems with motors WITHOUT a thermostat in them (must install a restrictor) because it lets the coolant flow to fast thru the rad and not dissipate its heat into the air.


Without a thermostat the motor will take a long time to come up to temperature.
Why do you not use a thermostat ?

[Kevin45]

I'm surprised no one has asked about the fans thermostats. Do they come on at a certain temperature or do they run constantly. If thermostatically controlled, does the car start to overheat by the time they kick on. Next...has the water pump been replaced. If so, where did you get it and are you sure it is the CORRECT one? It could be the fact that if the water pump was changed, you have one for a serpentine system when you should have one for a belt system. A serpentine pump will pump the water backwards causing an overheating problem. Also are the electric fans correct. By that I mean, are they a pull fan or actually a push fan? Lastly, before getting rid of the bike (if you don't want to get rid of it) ask around for a standard clutch fan and a shroud even if just to try. I got rid of a good fan not to long ago. If I still had it, you would have been more than welcome to it. You should be able to get one for next to nothing.

[Arrowhead]

Originally Posted by 75gmck25

I've had similar high speed overheating problems with my '75 GMC pickup, and have not yet figured out the cause. I could leave the truck idling in my driveway for hours and it would not overheat, but if I drive it at 70 mph the temp will slowly climb until it hits about 230 and I decide to pull over and drive slower (about 45 mph) until it cools down. Thermostat temp does not seem to matter, since I've tried both a 195 and a 180 and did not see a change in the overheating problem.

My truck has a GMPP 290 HP 350 with Edelbrock carb and manifold, but the rest of the cooling system is stock. Nearly all of the cooling system parts were replaced when I put the new engine in a couple of years ago, with some minor changes (Mr. Gasket high flow thermostat and Hayden HD fan clutch). The OEM shroud and steel fan are still there and the heater is fully functional. I'm using a GMPP HEI distributor with 12 degrees initial, about another 20 from mechanical, and about 18 more from the vacuum advance (using the manifold vacuum port).

One recent discovery was that the steel vacuum line to the TH350 had a hole worn in it from resting across the top, rear corner of the exhaust manifold. I don't know if this vacuum leak could be part of the high speed overheating problem. I haven't had the truck out on the highway to test it since I found the bad steel line and replaced it.

Bruce

Bruce, I'm having the same problem with my mustang I just put on the road after a 2 year build.

I just intently read every reply to this post and got a lot of good ideas.

I'm seriously thinking I have a sludged up block, even though it's been flushed mutilple times till it ran clear. I just put a new 3 core radiator in last night and it still gets hot on the highway. This morning I popped the radiator cap and and I can see a very fine silt sitting inside the new radiator.

Don't want to highjack this thread, but I think that's next place I'm going to look. I'm going to try to pull any drain plugs and see if I can flush the block.