Overheating after shut down

[valestrom]

So recently it's been pretty warm around where I am (30c/86f) and I noticed an issue that I can't quite place. While I'm driving the car I seem to have no issues, the car stays at a happy operating temperature, doesn't overheat, no sign of boilover, running a good AFR.

But as soon as I park the car, and shut it off it boils. I mean I hear coolant boiling, not sure from where, but it quickly expands from heating up, overfills my overflow and begins to dump on the ground. If i turn it back on, and it begins to cool itself again of course the coolant contracts and it starts to suck the coolant back in.

I'm not sure where my issue is and I've been looking for similar issues, but haven't found any in my searches. Here's what I've done so far:
- Removed and tested thermostat
- Checked temp sensor for rad fan
- Refilled, and burped cooling system for 10 mins

Notable things about the car:
- 2G Auto AWD
- 16G turbo
- 1G BOV
- 3" O2 back
- Boost leak test recently. No big leaks.
- Innovate Wideband
- Glowshift boost gauge
- All cooling hoses replaced with silicone
- Engine rebuilt ~ 700 km ago
- Lumpy idle, high in park, low in gear
- When driving it feels fine, builds and holds boost, no temperature issues
- No top heatshield, and might not have bottom (can't recall without looking)

Just looking for insight on where to look for issues. Thanks a ton.

 

[pauleyman]

Check the fluid itself for proper mixture and check/test/replace the cap.

 

[Vegas Smith]

Fans may not be turning on either.

 

[valestrom]

Check the fluid itself for proper mixture and check/test/replace the cap.

Sorry I didn't add, fluid is good, tested with a refractometer, haven't replaced cap, might still be OE. I'll replace it for good measure.

Fans may not be turning on either.

Fans are running while car is running, as it isn't until they shut off after you shut the car down that the issue exists.

 

[Sbgriffin]

I'd pressure test it, make sure it holds for at least 8 hours. Also I'd flush your radiator/ cooling system.

 

[valestrom]

I'd pressure test it, make sure it holds for at least 8 hours. Also I'd flush your radiator/ cooling system.

Yeah I'm kinda scared that it might be something bigger than a cap and I'll be ripping out the engine again. But I'll pressure test it this weekend and see how it holds. In terms of caps, do people generally run 13 or 16psi caps on these cars?

 

[Sbgriffin]

So my cap says 1.1 on it, I'm guessing that's bar. So that would be 16 psi. Also a proper pressure test on your coolant system will lead you to many different causes. I recently seen jafromobiles YouTube video on this. You should watch, it's definitely worth the few minutes of your life. Good luck, and keep us posted.

 

[motomattx]

My vote is cap and clean the corrosion in the housing that is keeping the rubber cap seal from seating.

 

[pat white]

boil over on shut down ...yup it's the cap

 

[Sbgriffin]

I agree, be the cheapest place to start anyway. I know you said you checked the thermostat. But did you throw it in pot with water to boil and watch for it to open? And use a cooking thermometer to see what temp it opens. That's an old trick.

 

[85Entropy]

My 4Runner used to do this. As soon as I replaced the radiator cap, it never did it again.

 

[valestrom]

I agree, be the cheapest place to start anyway. I know you said you checked the thermostat. But did you throw it in pot with water to boil and watch for it to open? And use a cooking thermometer to see what temp it opens. That's an old trick.

Yup, opened right when it was supposed to. Thinking about it the cap makes sense as being the fault, I've just never experienced a faulty cap before, gonna replace it sometime this week and see if the issue persists afterwards.

 

[valestrom]

So I forgot to reply to this, after I replaced my cap I haven't seen it happen since. However it hasn't been quite as hot out as it was the problem days. Comparing the two caps however my old one had very little spring tension left so I'll go out on a limb and say that's one of my issues fixed.

 

[Sbgriffin]

Yeah your cured I bet. Glad that's all it was man. Thank the DSM gods it was a cheap fix, most the time not so much.