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Thermostat housing leak

How would bad radiator cap explain combustion gases in the cooling system? He says he has confirmed headgasket leak (post #12). New radiator cap won't fix that . . . .
 



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The cap is supposed to vent to the reserve tank when it reaches 16 lbs or under depending upon the pressure rating on the cap. It's obviously not venting since the cap on the reserve tank would have popped off before the thermostat housing cracked.

Signs of bad head gaskets are traces of coolant mixing with oil, over heating, loss of coolant, oxygen sensors going bad from coolant, contaminated spark plugs, vapor smoking in the exhaust, and possibly other symptoms. There are no engine codes present or any other signs present other than cracked thermostat housings of unknown quality.
 






The cap is supposed to vent to the reserve tank when it reaches 16 lbs or under depending upon the pressure rating on the cap. It's obviously not venting since the cap on the reserve tank would have popped off before the thermostat housing cracked.

Signs of bad head gaskets are traces of coolant mixing with oil, over heating, loss of coolant, oxygen sensors going bad from coolant, contaminated spark plugs, vapor smoking in the exhaust, and possibly other symptoms. There are no engine codes present or any other signs present other than cracked thermostat housings of unknown quality.

And so your answer to the question ("How would bad radiator cap explain combustion gases in the cooling system?") is . . . ?
 






I'm not convinced that exhaust gas is leaking into the cooling system. Did the mechanic connect a pressure gauge to the radiator to see what kind of pressure builds up with the engine running for a few minutes?
 






According to Autozone's website, it shows that the radiator uses a twist on cap just like other radiators. https://m.autozone.com/cooling-heat...alast-radiator-c2310/233579_88571_0?location=

The Ford part does not show a radiator cap: Radiator | FordUS . My '02 did not have one, either (just the screw on plastic, large diameter one on the reserve bottle). So unless he bought a Duralast radiator, there's no cap at the top of the radiator.

I suspect that the remoteness of the reserve/overflow coolant bottle on the 3rd gen explains why the thermostat housing is taking the punishment of the excess pressure caused by the failed headgasket, rather than releasing pressure at the bottle (upstream).

I've never hear of a failed plastic screwcap on a 3rd gen, but I suppose anything's possible. Another problem with that theory is more fundamental, however: why is there excess pressure to begin with (without overheating). The OP has not identified overheating as related to any of this, just leaking coolant from a cracked t-housing. The diagnosed failed headgasket explains the pressure problem, which a failed radiator cap hypothesis does not.

Not sayin', just sayin' . . . .
 






AZ and OR have Radiator cap testers...

What happens is the pressure builds up when the cap does not vent fast enough to keep up with what is leaking in...

If you want to drive it, drill a 2mm hole in the cap so it can vent and increase your coolant mixture to 70% to prevent boiling.
 






The plastic reservoir cap is the pressure relief cap and will release at 16lbs regardless. It has two hoses to the cooling system so the system will always be under even pressure and will always be purging of air bubbles.

However, Ford used the same cap for everything. From little I4 engines all the way up to V8 diesels. When used in heavy duty applications these caps are notorious for failing and retaining 0 psi.

Also, the issue is not the exhaust gases leaking in and causing the coolant to boil. It's more of the fact that the gases leaking in form huge air pockets all throughout the cooling system and in the pump. This causes hot spots, poor circulation, lack of flow to the heater core & radiator, and ultimately a hot running engine. Changing the antifreeze ratio wont help.

Lastly, drilling a hole in the radiator cap will make it WORSE. Do not do this. You want the system under as much pressure as it can take. Higher pressure means its harder for the exhaust to leak in (everything travels from higher pressure to lower) and when under pressure the gas pockets will be smaller. Without pressure the gas pockets greatly increase in size further adding to the poor cooling.
 






Just to chuck in a comment re some earlier posts, I came across a company selling aftermarket thermostat housings in metal for 2002-2010 V6 4L Explorers.

Here's the link

2002-2010 Explorer Metal Thermostat Housing (SA2)

If I had known about this before I did my repair I think I would have gone for this option.

Cheers
Neil
 












Blown head gasket is the fundamental problem. Replace the plastic cap with one from a junkyard and see if it helps (cheap; probably useless IMHO). But wouldn't recommend throwing any more money in it other than replacing the head gaskets.
 






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