Overheating after new coolant expansion tank installed

So some context.
My 1988 Ford Escort's coolant expansion tank cracked not long ago, genuine Ford tanks are rare and expensive.

( It's a pressurised tank, with the inlet hose coming from the thermostat housing, and the outlet on the bottom going straight into the lower rad hose and water pump.

So i ordered an aftermarket one, installed it, everything seems ok, let the engine bleed the air out on its own with the cap off ( no bleed screws ), coolant right on the max line as it should be.

Then i decide to take it on a long ~60 mile drive each way to the beach, about half of the way into the trip ( driving on the highway at a normal 60-70mph the temp gauge starts creeping up, i pull over at a gas station and the engine is definetly hot but i open the cap on the tank and there is no pressure at all ( there should be ).

I let the engine idle until the temp gauge goes back down to about the middle, where it should be.

The rest of the trip i decided on getting off the highway and making my way there on a normal country road, the engine did not overheat and stayed at a normal temp.

On the way back home about 6 hours later i did the same thing and again hot home fine.

Then i noticed the cap doesn't seem to fit quite right, if you tighten it too much, it goes loose.
( plastic tank and cap )

So i returned the tank and they sent me another one.

This time the cap seems to fit better and close right, but still after driving for about an hour the engine starts getting too hot.

I don't understand where the pressure is going, if the cap fits right.

With the engine hot if you open the cap you should hear a clear "pssshhhhh" of the pressure escaping, it doesn't have even a little pressure.

Hope you can give me some new ideas because i don't know what to do, other than scour ebay for a genuine new old stock one that costs 150 bucks, or buy a nasty old used one.

By the way, the coolant is very clean and the water pump was replaced 2 years ago, it has never had any overheating problems before...
 

FordCapriDriver

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By the way, the coolant does not boil, and it never has, i am certain before anyone comments on this that it is not a head gasket problem.

Also, It took a month for the replacement tank to arrive after i returned it, i managed to patch the original tank so it wouldn't leak and for the past month have been driving it without a problem with no overheating.

Today the replacement tank arrived and it did the same thing as with the other one i bought, the gauge does not go all the way to the red but it does go above normal , about 3/4.
 
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There is a question here somewhere?

You could find leaks other than the cap with a pressure tester that screws on in place of the cap.
 
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The tank does sound like the problem, but how it’s causing a problem doesn’t come from its inability to hold the system under pressure IMHO. If pressure were the issue, it would have boiled over. If it hasn’t boiled over, I don’t see what role pressure, or a lack thereof, can play here.

Maybe get an infrared thermometer and start taking measurements everywhere along the cooling system to find out where the hotter-than-normal temps are starting. Once identified, work backward toward the previous part or section in the cooling system to try to identify what’s not behaving as it should and how the coolant recovery tank can interact with it to make it not work right.
 

JHZR2

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You sure you didn’t get an air bubble trapped somewhere?

Does some quantity of coolant constantly flow through the bottle? Think my Saab was set up like that. If so, a bad orifice, or obstruction might cause stagnation?
 
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I replaced the OE tank on The Bacon Hauler with an aftermarket one and kept the OE cap to use on it. Turns out that OE cap was a poor fit for the aftermarket tank’s neck - wouldn’t seal the system up.

I had to get an aftermarket cap (Stant?) to use on that aftermarket tank eventually. Once I did that, everything operated as expected.

Try a different radiator cap, an aftermarket one.
 
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Something doesn’t jive with all this. Coolant in an unpressurized system should boil over at 212F, and the OP stated there have been no boil overs. So the coolant must not be getting above 212F, which is hotter than it should be running, yes, but hardly an overheat situation.

I‘m not saying there isn’t a problem somewhere, but if it won’t get over 212F, it’s a minor annoyance at best right now. Something to be diagnosed for sure, but not something to keep one awake at night IMHO.
 

FordCapriDriver

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1- Yes the system is properly bled and no there are no bleed screws anywhere.
2 - I might try buying a new cap which is the same brand as the cap.
3 - Will probably replace the thermostat even though i am fairly certain the problem isn't there.

Thanks for the replies
 

FordCapriDriver

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You sure you didn’t get an air bubble trapped somewhere?

Does some quantity of coolant constantly flow through the bottle? Think my Saab was set up like that. If so, a bad orifice, or obstruction might cause stagnation?

A lot of coolant flows through it, it holds about a liter of coolant, the coolant comes in from the thermostat housing and out to the lower rad hose.
 
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Seems simple fix to me. Buy an OEM tank. ;)

Replacement engines are more expensive than coolant expansion tanks
 
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Drill a small hole in the OE tank and see if running it behaves the same as the aftermarket tank. If not, the aftermarket tank’s pressure leaking isn’t the underlying issue. Maybe it’s inlet or outlet tubes are smaller diameter or something. Hard to know for sure without access to it, but I still think the pressure issue is a red herring in this situation.
 
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