Hot Rods 400 sbc highway speeds sudden overheat

Standard deal on all circle track using a SBC if allowed. Every engine we build for ours has these hoses. You can see them on the enclosed photo of our back-up engine

 

jaracer post, I had Sprint car engines 400 steel block and the water lines were plumbed from back and front of heads to radiator, Suggest you do research on factory 400 GM passenger cars, I agree could be air is trapped. Is your radiator top above cylinder head or below, if below so you need to plumb in a remote radiator top tank so air is not trapped in heads.

 

Back when in the 70's the hot racing setup was a 400 block with a 350 crank. It got you about 372 cubic inch. I never had a problem with the 400 blocks with this setup. I put together a stock bore and stroke 400, but the cast crank was soft compared to the forged 350 crank. The rod throws were badly worn after one season.

 

The Aftermarket made the 383” what it is today... but to me was always backwards. The 372” or opened up a bit 377” was a much better combo.
Now using a 3.875” crank in an aftermarket block is the way to go especially on circle tracks. All off the shelf parts that can blow the tires off anytime. We started with a 417 but are bigger now....

 

JA racer and Jimmy six are 100% correct !

Depending on the build , we sometimes take the steam/ water from the rear of the intake and put it into an expansion tank. From the expansion tank back to the suction side of the water pump.
The suction encourages the air pocket / steam to leave the block ..
Just taking the water/ steam from the back of the engine ( whatever method used) seems to drop the temp at least 20 degrees..

Kind of a standard setup for me includes this short list.
Water out the back of the intake.
Several 3/ 16 " holes in the thermostat.
GOOD , proper fan shroud ( with 1/3 to 1/2 of the fan blade OUT of the shroud.
If possible , double or triple pass the radiator.

Lots of horsepower cooled this way..

Remember folks....
Engines burn fuel to create energy ( heat )

Heat is horsepower !

General principles...
1/3 heat turns the crankshaft
1/ 3 heat to the cooling system
1/ 3 wasted out the exhaust.

This is why turbocharging is so effective !

Sorry...
Another long winded reply..

Dave


Sent from my SM-G973U using The H.A.M.B. mobile app

 

I agree, this will help determine if the problem is an air pocket as it keeps a small amount of air form accumulating under the thermostat, where it could keep it closed and not allow to open up until that steam pocket gets hot enough then it finally opens. Only consequence of this is slightly longer to warm up since even that 1/8 hole does flow a bit of coolant until the thermostat is open.

 

Ya ain’t got to worry about that in Bama.

 

Has car always done this ?
Long water pump ?
High flow water pump ?
Do you have aluminum heads ?
Where is your timing, vacuum Advance hooked to full manifold ?

Your radiator seems a little on the light side to me.

 

Important question IMO. You do say it's not overheating but still not really right. Is this something that started after owning the car for awhile or a has it happened since you owned it?

 

The HA/GR in my avatar has the radiator cap level with the highest point on the block. If refilling with coolant I jack the front of the car up as high as possible to allow all the trapped air to escape. I also run an overflow/ recovery system.

 

i had a similar problem and yeah 3 lil holes in the thermo disc cured it. like magic.

 

I replaced the thermostat in my avatar because the car would not get warm. 351 Windsor. Thermostat had 6 holes drilled in it. Car came out of AZ so maybe necessary there. The new thermostat already had a hole in it with a little check valve.

 

ran car again this past weekend. Added some coolant as level had gone down some I think the air pockets worked their way out. However now temp starts to slowly climb at hwy speeds (215-220ish) but will cool off at idle. To answer your question, camel hump heads, recently hooked up vacuum advance to full manifold. Water pump is not high flow. Could be timing or carb problem.

 

Simply not enough radiator! Or it is plugged.

Ben

 

The heating up when at highway and then cooling off at idle is opposite of most vehicles. Just dumb question, is you fan installed so it pulls air correctly? If fan is right, then it seems your radiator is needing repair or replacement, it just can't remove enough heat.

 

Sounds like the radiator is too small. Or there's a restriction in flow. Lippy

 

If your cruising @ 215-220ish MPH I think the problem is the air can get out fast enough

 

NOT all water pumps are created equal! Try a different one. Had the same issue with my FI 283... rodded the radiator, 2 thermostats (Superstant, than a RobertShaw). I KNOW it helped, but the gauge didn't reflect it. Bumped the fan while measuring for a shroud, noticed a bit of play. Replaced it with a new rice pump from NAPA, won't go past 200 on the hottest days! Consider a pump from Steward Racing - cast or aluminum... Good Luck!

 

Might be cavitation in the water pump at highway speed revs. I would try a new water pump. New, not second hand.
The price of a good brand new pump is a fraction of the price for a new or rebuilt engine................