Coolant boiling in reserve tank

[Davejam]

Originally Posted by mk378
You guys are all the reverse of the typical car owner who comes to a forum convinced up and down that there is no way my head gasket could be bad.

To review, as a doctor would say, the "presenting symptom" was overheating while idling for a long wait in a drive-thru line. If further questioning can differentiate it down to overheating only when the car is not moving, the radiator fan system is the primary suspect.


You didn't read through the posts. A few posts above: "Good news on the fans. With the cab blower fan on, they run."
Its possible its a coolant temp fan switch, so I would just idle until early signs of overheat without blower on. If fan doesn't come on research if your vehicle has a switch or relay or what.

There was also troubleshooting presented to rule in/out Head Gasket issue, which still seems like a very likely cause.

 

[CNAKitty]

Yes they came on the other night when I checked. Running the heater on HIGH has allowed me to baby it enough to get back and forth to work last 2 nights w/o overheating again at the slower speeds. I'm replacing both hoses, all coolant, thermostat, cap, and go from there. I wanted to replace the reservoir this afternoon as well, but none in stock for my model. I'm going to remove and clean the one here, and if it looks like it really needs replaced now, I'll get a universal one and drill the necessary holes.

 

[CNAKitty]

Thanks. Since the radiator is all gunky as witness my poor cap, I'm still going with original plan of drain, flush & refill now that I have a night off. I'm replacing both hoses, even new clamps, ALL coolant, thermostat, and radiator cap with quality new ones. I WOULD replace the reservoir tank as well if they had mine in stock. (they have a universal I would need to drill holes for and if it comes up as necessary, I'll go that route) I'm also going to check the water pump, and get/borrow a combustion tester if I can to check that as well. The fans run when I turn the AC/Heat on, but I'm also going to check the temp sensor since the gauge is only showing the temp at the 1/2 mark when it's boiling in reservoir. I appreciate all the help you guys gave me these past few nights. I was too busy working and sleeping to respond until now.

 

[CNAKitty]

Thanks. The thing is, even though I was needing to add so much coolant at first, I'm not seeing evidence of a bad leak on the pavement under car. I'm thinking it was the fact that it had mostly water, not coolant, it was evaporating/boiling down, since I started topping it up with the 50/50 Peak coolant it hasn't dropped as often or as severely.

 

[CNAKitty]

Here's pictures of my cap. The first one shows how gunky it was STILL after cleaning with a paper towel. The second, misnamed one shows after I scrubbed it with dishsoap and a good scrub sponge. I'm still replacing it today.

 

[caprice_2nv]

If it was boiling at half on the gauge, it's either combustion gases from a head gasket as was already suggested, or being mostly water could lower the boiling point enough for that to happen I suppose.