Random Overheating

2012 Gen3 Prius.. 190k on the clock. Past couple of weeks I've had random temp light pop up. 15-30 seconds and then it's gone. Always under acceleration but not necessarily heavy or consistent. Ex 2 hr interstate roundtrip.. got the light one time. It's eluded my attempts to catch it and check the temp with Torque thus far.

This last time.. 1.5 hr into a 2 hr interstate trip and it popped up again, this time set a CEL, I think just due to the number of cycles. P0117 - ECT low input (high temp). Checked and I lost a little coolant out of the reservoir (spewed). Oil looks clean though. This was an oil burner, but did a full EGR replace 30K ago and that stemmed the oil burn significantly.

Head gasket starting to go is the only thing that makes sense to me. Air in the cooling system shouldn't cause the over pressurization/spewing should it? Any other ideas or things to check?

 

The fact that it only seems to occur under extended load makes me think it's not pump/system related. I'm not losing any coolant unless an overheat episode occurs.

Yeah EGR definitely helped though I'm sure damage had already occurred as oil ran low several times prior to that. Through the multiple oil changes, none of the dealerships thought to mention to me that it was low at each change. I started handling everything myself after I got the low oil light. Pre EGR oil consumption was 1 qt /500 miles.. post - 1qt / 1500-2000. I know it's not fixed but I was just hoping to buy another 100k out of the engine.

 

It's the only thing that makes sense to me. I think it's certainly at the early stages now. I had to make it home yesterday on a 3 hr ride.. stayed out of the power band as much as I could and monitored temps with Torque. No issues at all even at extended highway speeds. Temp never got above 200. Looking at older threads the consensus on this forum seems to be HG replacement is not worth it, and just to swap the engine. Not sure why exactly. I may just push this engine until it blows, but the Prius is my long-haul vehicle and that doesn't inspire confidence on 1000+ mile trips.

 

If it's the reservoir cap it shouldn't lead to overheating provided there is sufficient coolant though? I'm not losing any coolant aside from the overheating episodes where a small amount blows out. Not following you on the EGR.. rings were likely already too far gone to fix by the time I discovered the oil consumption issue. The EGR re-do resolved the misfires and side effects that come with clogged pipes. No doubt it will clog again, but the other alternative was engine rebuild or replace. So the cost of parts bought me some time and miles.

 

Fair enough. Any experience with swaps? I've done HG on a few cars before, never an engine swap. If a Prius swap is fairly straightforward, I'd be willing to give it a go. I am concerned that the ring issue was never truly fixed on this engine. I discovered my oil issue 'early-on' at around 120k.

 

This could be due to a failing water pump also, right? That should normally set some kind of code? Looking around at past posts, it seems a cooling system test may not tell me much. Also having trouble finding an adapter that works with the reservoir (aka cap-less radiator). Just making sure I explore all options before throwing in the towel on the engine.

 

Mentioning that because I was poking around today and heard a pinging/ringing sound from passenger side of engine after cut off for a bit. Couldn't isolate it to water pump but it sounds possible. It seems like dying pumps tend to set codes in these cars and I am not getting anything pump related. However it makes me wonder since I am getting no discernable coolant leakage aside from pressure release. Also, noticed it seems to happen most often in the first 15 min of a trip, and once it occurs it does not happen again. Not sure what to make of that, or if a warming engine has anything to do with it.

 

That's actually a great point. I assumed faulty tstat would just fail open but hadn't thought about a sticky one. In fact, all of the overheat episodes except for one have been 5-10 min in. That one was 1.5 hr in on a highway trip.. I guess it could have been low coolant related but it was not excessively low. But it threw me off.

I was able to replicate it today in maint mode parked in an attempt to bleed air out. Car warmed up. I kept it at 2500rpm, so no excessive load. Temps slowly climbed as expected but did not drop off at ~190. Got to 220, system pressurized and blew coolant. Then right back down to normal range. Went from 190-220 and back to 190 in under a minute. I will investigate the tstat angle further tomorrow.

 

IIRC from doing the EGR, it's at lower front of engine? I guess it would mean a full drain, think I'll just go ahead and replace the tstat and see what happens.