The radiator cap is what controls pressure in the cooling system. Isn't anyone gonna suggest trying a new cap?? If your mechanic actually tested the cap (I it's OK), maybe he can explain a little better what he means by the pressure being too high.

There's 2 or 3 places on the radiator neck where the cap seals against. Make sure they're clean & don't have gouges...

 

i dont spose that should cost 800-900

 

But if water is coming out of the exhaust, I think there's a headgasket leak.

 

i just talked to him
he said because it overheated before the gasket most likely has a leak so the head will have to be taken to a machinist to resurface
hence the $800+

if i get the head off myself how much will the resurfacing cost?

this is the last time i let my gf talk to a mechanic h:

 

I dont know how much resurfacing costs....call around to various machine shops that do engine work...shouldn't be too much. Overheating can most definitely cause the head to warp, which in turn causes the gasket to not seal properly.

 

Well, earlier he said the HG is OK since it was replaced not long ago... Now it's not OK because ???

If he's removing the head, resurfacing, (maybe resurfacing the block too??) that explains the high cost.

I can't see the engine firsthand, your mechanic CAN. There's some amount of sooty water that's normal in the exhaust, especially when the engine's cold. I can't see how much is there, to compare against what I think is 'normal'. When it's running & spitting sooty water, does the exhaust smell sweet like antifreeze?

You say your mechanic's reliable, and I'll say a warped head after overheating is certainly possible... If you feel like doubting him, there's ways to test. For example the antifreeze can be tested for combustion gases. Or you can get a leakdown test.

 

i dont doubt him
i doubt my gf

another had looked at it before and said antifreeze

at any rate we're gonna get rid of it
thanks for the help

 

It's a tercel. Don't waste your time or money.

 

The radiator cap doesn't control the pressure, it's only an emergency vent for when pressure gets to high. All it does is bypass antifreeze into the overflow bottle when the pressure gets excessively high. This saves the heater hoses from blowing, dumping out all the coolant, and leaving you stranded on the side of the road.

It does the same job as a pop-off valve (not to be confused with a blow off valve, they are different) in a good turbo system.
I doubt it would be over $100. Hell, a used Tercel head should only be about that, and a rebuilt one in the $300 range.

 

I guess I don't particularly know Toyotas. On the VWs & Saabs I've had, the reservoir is pressurized & it has a vapor-space. The cap only vents overpressure. I figured it was some kind of Europe vs. Japan tradition in how they're designed. If Toyotas have a vapor-space, then you're right.

Honda cooling systems don't have any pressurized air space, so the cap does control pressure by releasing coolant over to the reservoir as it heats up. On cooldown it sucks coolant back in so there's no air space. That's why there's 3 seals on the cap instead of just 2.

It's a spring-loaded poppet valve, so it works like you say. That's how it controls pressure in the system.