[hoodooman]

Ok, I'm back on this issue. I took my heads to the machine shop and had them pressure checked. I had one leaky exhaust valve that they fixed. They also ended up having to cut the heads .006 because they said there were "low pockets" in the middle that they said could have caused my overheating and oil/antifreeze mix issue. So, newly machined heads, new head gaskets, intake gaskets etc. The car is still having issues. I let it idle in my driveway - no issues. I took off around the neighborhood - no issues yet. Then I parked it and revved it up a good bit. The temp immediately spiked to about 230 from 160 and I shut it down for a while. I do not see any oil/antifreeze mixing at this point but the radiator and top hose build up a ton of pressure when it overheats.

Here's what i've done:

• had heads check for cracks and milled .006, new gaskets all around. head gaskets are confirmed installed in the correct orientation.
• two different water pumps
• 4 different thermostats
• two heater cores
• all new hoses
• two different temp gauges

The only things I can think at this point are:

• radiator clogged with crap from my old, dirty 289
• cracked block
• warped aluminum intake

I don't see any leaks anywhere at this point.

What gives?

 

[a793aa]

Hoodooman, you mentioned performing cylinder compression tests cold. Performing it at engine operating temp is recommended. It might be helpful to test your engine under thermal conditions in case metals are expanding.
Also, did you say you ran the engine at idle with the thermostat open to look for normal flow or abnormal pressure? I am reacting to your statement regarding your additional pressure when overheat.

 

[hoodooman]

Hoodooman, you mentioned performing cylinder compression tests cold. Performing it at engine operating temp is recommended. It might be helpful to test your engine under thermal conditions in case metals are expanding.
Also, did you say you ran the engine at idle with the thermostat open to look for normal flow or abnormal pressure? I am reacting to your statement regarding your additional pressure when overheat.

Thanks for the thoughts. I have not done compression or leakdown tests at operating temps. I should do that next. I did run it at idle, but not without a thermostat. I should also look into this. thank you.

 

[a793aa]

If you take your thermostat out, then you would be about to idle with the engine cold which might be safer of course.

 

[64-1/2 first.... 66 now]

What makes you think your radiator and top hose are building up a ''ton'' of pressure? If the radiator cap is relieving, it could be bad causing the boiling point to lower. I think I'd get the radiator checked also.
Pulled this from the internet -
A coolant mixture of 50% water and 50% ethylene glycol has a boiling point of 223 degrees. A system with 15 psi cap will add 45 degrees for a final boiling point of 268 degrees. The real purpose of pressurizing is to give drivers a higher operating zone in case of extreme conditions. For example, let’s say your classic car normally runs at 180-190 and boiling is not a concern. Then on a hot day the temperature goes to 200-210. This is not a problem either but then traffic stops and you can’t move. Now the temperature starts to rise to 240 and without a pressurized system the coolant would boil and spew all over the place. The loss of coolant would eventually fill the radiator with air and the temperature would rise even higher. Remember, none of the above running temperatures have anything to do with the cap rating. They are simply conditions of the cooling systems capability, the ambient air temperature, and air flow.

 

[Vintage Ford Guy]

I have never had a air pocket get stuck in Mustang. There are cars that require you bleed the air out but this should not

The upper hose is the pressure side of the pump but the lower hose is the vacuum side. If you put a high volume water pump on there one thing that could be happening is it is collapsing the lower hose. Three is also a correlation between the amount of time the coolant spends in the radiator so the tubes can draw the heat out of it. That's why all super duper upgrade are not always the answer. Originally most hoses came with a wound inner wire that prevented the lower hose from collapsing from the suction of the water pump. Not all after market hoses come with them. I've seen plenty of mechanics just pull those wires right out of a new hose. I don't think they have a clue why they are there? Maybe some hose manufactures lower hoses are made out of material that will not collapse without the spring. Hoses use to come with them and now most do not?

Take a look at your lower hose and see if it is collapsing? Its one of those rare things you never see but read about.

Avoid This Mistake: Radiator Hose Collapse - Hot Rod

 

[Vintage Ford Guy]

Not true. An air pocket or low coolant can also make the temp sender read cold (no coolant in contact with it) then as soon as a shot of coolant goes past it will shoot right up.

In my experience that is only happens after draining the coolant system and getting air trapped behind the thermostat. The engine can get real hot because the coolant is not reaching the thermostat but once the thermostat does opens up the air is purged out and from then on out there will be coolant behind it. That does clause a rapid swing from hot to normal as the air pocket is purged out. After that is should never happen again. You do need to watch the temperature carefully after draing it and refilling it. If it goes much past normal and is still climbing you need to shut it off. The temperature continues to rise after you shut if off and sometimes that will get the thermostat to open. Sometimes you have to take out a temp sensor or remove a heart hose to let the air out so the intake can complete fill with coolant.

If you have thermostat with the little check valve and the valve is installed towards the top no air should be able to get trapped behind the thermostat. Do buy one without the one way valve.


Always install this air purge opening to the top. And be absolutely sure you do not install the thermostat backwards or you are going to have bigger problems. Sensing bulb goes towards the engine