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Tech501
Tech501, Auto Service Technician
Category: Car
Satisfied Customers: 747
Experience:  38 years exp, ASE Mastertech with L1 Advanced Engine performance
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I have a 1968 road runner with a 440ci 4bbl..runshot..cooldown

Customer Question

I have a 1968 road runner with a 440ci 4bbl.
It runs hot and will not cool down.
I have done and checked the following.
It has a new 26 inch 3 core radiator, new water pump, new 160 degree thermostat. shroud on radiator, new viscous thermal fan.

Symptom: it warms up properly to about 170. Then if i am in slow traffic the engine temp will creep and will not come down. I do not see bubbles in the antifreeze. No white smoke in the exhaust. Even running the heater on full high will not make the engine temp drop. I do feel a ggod amount of air coming through the radator as well as good water flow. What could be wrong.
Submitted: 11 years ago.
Category: Car
Expert:  Tech501 replied 11 years ago.

Is it consuming any coolant?


Is this engine stock?


What's been done to the engine?

Customer: replied 11 years ago.
Reply to Tech501's Post: It is not consuming antifreeze or oil.

As far as the engine goes it sounds like itis a mild cam. It still produces 18 inches of vacuum.

thanks

Dan
Expert:  Steve replied 11 years ago.

If it is an air conditioned vehicle, make sure that there is not an accumulation of road dirt, bugs, or other material restricting airflow through the condenser; you would be amazed what a pressure washer will flush out of there! Remember, all of the air must makee it through the condenser core before flowing through the radiator.


Even though you aren't showing any other symptoms yet, performing the chemical test for traces of exhaust gas in the coolant might be helpful, just as a double check. I have seen a couple 440s which had blown head gaskets (years back).


If the engine has an exhaust heat riser/ crossover through the heads to warm the carb base on a cold engine (I dont recall if this car has one and none of my manuals go back that far), make sure that the heat riser valve is fully open when the engine is warm. This may involve dropping the header pipe enough to physically inspect the valve to make sure the butterfly has not come loose on the shaft.



It does sound like you have covered most potential problems already. Perhaps trying another thermostat? If it is a discount parts store thermostat and not an OE one, it may not be opening fully. It might be interesting to try removing the thermostat temporarily to see if the problem goes away.


That is pretty much all that occurs to me at this time, if we think of anything else I'll be sure to let you know.


If I can be of any further assistance, please do not hesitate to ask...


Expert:  Tech501 replied 11 years ago.
There has been no "boreing" done to this, right?
Customer: replied 11 years ago.
Reply to Tech501's Post: I do not know. I have not opened the engine but i do know it had to have some work done to it. It pumps 75 lbs of oil pressure which is not a stock pump.
Expert:  Steve replied 11 years ago.
Just a note; having worked on many engines back in the days when oversize boring during rebuilds was commonplace, I have never seen the slight increase in displacement from boring even as much as .040" oversize ever cause an overheating concern as long as the head gaskets were sealing properly. If the engine was operating normally up untill recently and no modifications were performed at the point where the overheating problem developed, it is probably safe to conclude that modifications are not the root cause of the failure here.
Expert:  Tech501 replied 11 years ago.

No it's not safe to conclude modifications aren't the root of the problem. I have seen many an engine suffer from overheating due to cylinder boring and a thinner wall between the cooling jacket and the heat generated fron cylinder combustion, especially if the head had been shaved or the pistons changed, increasing the compression ratio and in turn the heat generated.


Another note is that thermal fan is something we never liked on those engines. We always tried to use some type of flex blade fan that would pull more air at idle and less drag at RPM.


Also make sure one of the modifications they made for more power wasn't changing the crankshaft pulley with a smaller one to reduce accessory RPM. That gains a little power but causes problems like this.

Expert:  Tech501 replied 11 years ago.
I've posted some specific issues to address but you will have to post the deposit before being able to view them. Please click on my accept button after viewing. I will be happy to follow up with ang further questions you may have.
Expert:  Steve replied 11 years ago.
I have posted several potential fizes for the problem you are having, if you find my response to be helpful, of if I can be of any further assistance, please consider clicking on my accept button, as that is the only way we specialists can receive payment for our answers; thanks!
Expert:  Steve replied 11 years ago.
If the boring was done immediately prior to the engine overheating issure occurring, then it could be a remote possibility; however the customer here states that he has made no modifications to this engine. If the overheating problem has recently started occurring, then this is not the cause, as it was like that previously and ran OK.
Expert:  Tech501 replied 11 years ago.
This customer stated he DIDN'T KNOW what if any modifications were made and never stated how long he's owned the vehicle or anything about not have the problem prior to this.

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