No.
Without pressure on the cooling system the coolant will boil at 220 F.
If the cap is removed when the cooling system is 250 F, most of the boiling coolant will be discharged from the cooling system. Don’t try this, it could be fatal.
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The very first sentence in the very first reply (by yours truly) addressed the issue of coolant pressurization.
Now, 13 days and 19 replies later, someone suggests doing something that could get the OP scalded.
I’ve had 2 friends go to the ER for this kind of thing. It’s not pretty.
Bad advice can be worse than none at all.
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The heads and block were machined, but I don’t know how much material was removed. The machine shop ordered new std pistons and rings, so I think the cylinders were only honed. I didn’t put any coating on the head gaskets. The radiator is new.
I believe there is either air trapped in the system I am unable to purge, or more likey at this point, air somehow entering the system. I’m going to pressurized the radiator again today to look for leaks.
How much pressure can I safely put in the system? 15psi didn’t show any leaks.
Something else you can do is to put the pressure tester on the cold engine and do not pump (zero pressure) and then start the engine and watch the pressure, it will show you a lot about what the cooling system is doing… If the pressure starts climbing much faster then the temp is rising then you have combustion entering in the cooling system… Remember to not release the pressure while hot or you could burn yourself in a bad way…
I went to the FEL-PRO Web site and looked up your application, 2002 Subaru Forester, 2.5L H4 2458cc, and I am sorry to say, the web page is quite specific, that the head bolts MUST be replaced and are not included…
The web page also goes on to say, “Please refer to Additional Fit Criteria for a more precise match…” which I guess it means to call them to ensure that the version of your engine is correct. Perhaps referring to the engine being manufactured in different plants from slightly different castings…
There have been so many suggestions and so many attempts to analyze the cause, but the suggestion about the head gasket is perhaps the most likely cause. Perhaps the head gasket for your specific “block design” only approximates the original and perhaps a passage that is needed between the block and head is not there. Oh, I l know it’s the most severe and expensive option to check that exists, but if the head gasket’s proper design cannot be verified to include every coolant passages is provided and that each passage is clear, then what other option do you have, drive it fast to keep it from overheating?
And while the head is off, I would shove a bent (hooked) coat hanger down and into every coolant passage to ensure that the machinist who did the heads and block did not “lose” a rag while preventing metal chips from entering the coolant passages…
600 miles on an overhauled engine is not much. They can be very tight for a few thousand miles and generate more heat. I didn’t even dare shut my Gm crate engine off for 200 miles fearing it would not start again. I recall having to replace the batteries shortly afterward also. Get some miles on it and sure check for head gasket problems. I rest my case though on never overhauling an engine unless it’s for a tractor.
Overheating in my world means coolant spray under hood. Your situation is hot temp on gauge and gurgling? Your motor compartment is dry?
Correct. The way I do it on my cars – may not apply to every car of course – is open the radiator cap when engine is cold, then idle the engine and feel the top hose as the coolant warms up enough to open the thermostat. At that point I can get a sense of the amount of coolant flow pouring into the top of the radiator.
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I asked because in two cases where I’ve had heads machined, the engines were prone to run hotter when run under a load.
Thinking more on it now, I don’t think this is happening to you, because you state the overheating occurs at slow speeds or when you’re idling. There’s no big load on the engine in those conditions.
This is a tough one.
Is there any way you can see if any of the four cylinders is running appreciably hotter than the others?
I ask that because you say the engine cools down if you rev it. I wonder if a cylinder is overly hot and the increased coolant flow from reving is enough to help it.