99 4cyl coolant leaking out of reservoir vent tube

[coldday]

Was out driving maybe 4 miles at lunch today. Parked, came back about 45 min later and drive maybe 3 miles when I notice the temp gauge at "H" so I pull over, stop the car, pop the hood and notice coolant spewing out of the vent tube of the coolant reservoir. It subsided quickly. The fan was on for short bit then turned off. Drove it the last 2 or 3 miles back to work, needy temp needle nearing "H".

Thoughts: thermostat, but bottom hose was hot, upper not so hot, heater not putting out heat at one point, but later in that same last few miles started putting heat out. I put in a new 25 dollar thermostat from o'rielly maybe 6 or 8 months ago.

Cap: far as I could tell coolant was not boiling, cap isn't that old as I put a new radiator in a year or so ago.

Water pump... Could be.

Head gasket, new about 40 or 50k ago. Oil on dipstick and oil fill cap looked good.

Anybody ever experience anything like this? 177k but as stated rebuilt head at 130k. New radiator and thermostat < 1 year or so.

Going to pull and test thermostat, and if ok replace the water pump. Trying to get the fear of head gasket out of my head

Thanks for any thoughts!

[coldday]

Update.

I removed the thermostat housing. On the 2.2L the thermostat is embedded in the housing, one unit, no replacing just the thermostat. I dunked it into a pot (old) of boiling water and it opened about 1/4" or so. Would slowly close as it cooled once removed from the boiling water. Going to say the thermostat appears to be working.

Moving on, will be the water pump. Never personally done a water pump but I'll be doing it this weekend assuming I can get the part.

If anyone has any better ideas I'm all ears

[coldday]

Change in plans.

I'm going to buy another thermostat, boil this new one and see if it opens more or not. That will give me a better idea if my thermostat isn't opening all the way or what.

Also, going to buy a new compression tester from Harbor Freight - they have one that has an extension piece to push down into the spark plug hole, that will make it easier and will tell me if head gasket is toast - well that and the plug condition.

Hoping it is just the thermostat no opening all the way or reliably.

If thermostat doesn't do it and compression is good, I'll put in a new water pump.

Hey, I'm trying to keep this forum alive, what can I say?

[amigo-2k]

My guess is the cap is bad....

[coldday]

Originally Posted by amigo-2k

My guess is the cap is bad....

Thanks Amigo. Your post made me rethink it and I guess if the cap isn't holding pressure, the coolant may not be getting hot enough to open thermostat fully.

I have a spare cap somewhere so I'll give that a shot once I get the thermostat back on (have to cut a gasket, nobody had one).

Thanks to the reply! I'll update later.

[coldday]

Well put the thermostat back in. Drive till it "warmed" up to H just about. Neither radiator hose was hot, nor would the heater blow any heat, stone cold. Since I tested thermo and confirmed it opens, has to be water pump not cycling the coolant. New water pump (and timing belt since it has to come off) going in this weekend...

[coldday]

Well, new water pump and thermostat and issue not fixed. I'll try a new cap tomorrow, maybe back @sswards, otherwise blocked heater core maybe. Man

[coldday]

New cap didn't change a thing.

Had it towed to mechanic today. He says the radiator is clogged (buy a better radiator than a csf/cfs brand is my new formed opinion).

$320 for an all metal rad parts and labor.

Another infamous monologue by cold day...