Classic/Antique Car Repair: Overheating Mustang, rubber flap, mustang 289

Question
QUESTION: Hi Dick
My 65 Mustang (289 4bbl/automatic) tends to gradually overheat at speeds over 40mph. At low speed it runs right in the middle of the gauge. I've just put the car on the road after 10 years plus sitting. the rad has been recently rebuilt, I just put a 140 deg. Thermostat in it and had the timing checked. It doesn't have a fan shroud, but that seems to be the way they were. I'm wondering if a good cooling system flush is required? I'll appreciate any advice.

Peter

ANSWER: If it only overheats at high speed, and the power seems about right, the most likely cause is a collapsing lower radiator hose.  The hose should have a spring insert to prevent this, but many mechanics don't understand the physics involved and discard the spring.  So, when the car is cold, reach down and squeeze the lower hose - if you don't feel the spring through the rubber, that is very likely your problem.

If the fan and shrouding are all the way the factory built it, the car should not overheat.  Make sure there is no other problem (transmission cooler added in front of the radiator for example) and no way to air to bypass the radiator (bottom air deflector missing in front of the radiator for example) or missing rubber flap to seal the top of the radiator support to hood.

Check those things and see what you find - let me know and I'll try again if that doesn't help.

Dick

---------- FOLLOW-UP ----------

QUESTION: Hi Dick
I checked for missing parts and squeezed the lower rad hose as suggested. No spring! I went to purchase another hose and found that it didn't have one either. I put some hose clamps around the old lower hose thinking this might keep it from collapsing if this was what was happening anyway, but the car is still overheating. Seems like I can drive all day at 40 mph or less, but a few minutes at anything more and it boils. I'll appreciate any other tips.
Thanks for the previous advice.

Peter

Answer
There are a very large number of things that can make an engine run too hot, but since yours only overheats at high speed, the list is a bit shorter.  I'd still suspect the lower hose collapsing - and I advise you to buy one of the universal fit type that comes with an internal spring - they look like an accordion bellows on the outside - with ribs to assist in bending the hose - those ribs have metal springs in them.   Another way is to get a spring from some other source that will fit in the original style hose and stay there - but somehow, you've got to assure yourself that the hose isn't collapsing at high speeds (the water pump can pull a powerful vacuum at it's inlet!).

The other thing to investigate is the air path from the grill through the radiator - make sure there is no way for the air to go anywhere else except through the radiator.  Most cars have a rubber flap that hangs down from the underside of the hood to seal against the "core support" when the hood is closed, and the area in front of the radiator at the bottom of the car should be closed over by a pan of some sort.  Every bit of air that goes into the grille must go through the radiator.

If you've done all that, and it still overheats, you'll have to assume there is something wrong internally - most likely built up crud in the water jackets.   The next step would be to pop out one of the "core" plugs (AKA freeze out plugs) on the side of the block.  Pick the one closest to the back of the engine (those are always the most plugged up) - you may have to remove the starter to get at it, and dig around in there.  If there are spoonfuls of congealed mud in there, you've found a big part of the problem.  Pop out the rest of the plugs on both sides of the block (assuming we're talking about a V8) and clean and flush them all out - using hacksaw blades and screwdrivers and a high pressure garden hose nozzle to get ALL the crud out.  You'll be amazed!

If I didn't mention it before, make sure the car has the right fan on it, and that it is only 3/4 inch max from the radiator (but of course this is not as important at high speeds as at low speeds).

If there is anything at all that has been added in front of the radiator (AC condensor, Transmission cooler), remove them to see if that helps.

Beyond that, I'm stumped, assuming the engine has normal power and feels good driving it (because that proves it is tuned correctly and has no exhaust restriction or valve timing issues) which are other causes for overheating.

Let me know what you find out, please.

Dick