So a few weeks ago I was sitting on an on-ramp and my AC suddenly started blowing hot air. Looked down and noticed the car was overheating. Pulled over and had it towed back to my house. No steam from the front, no steam from the back, no massive puddle of coolant on the ground (I went back and drove the onramp an hour later in a different car to check).

As of right now, its pretty evident that the reservoir failed (230k and the original reservoir so no surprises). I haven't put the car into service mode to get a good look at the front, but there's no evidence of coolant anywhere other than the back of the engine bay, from the reservoir. Can anyone think of any reason to not chalk it up to the reservoir just giving up and spewing coolant everywhere?

I have a new reservoir on order as well as a new thermostat and housing (they were cheap)
I've replaced the oil and it's 100% coolant free so I'm assuming the head gasket is fine.

My only real concern is the water pump. The car is old and on the original supercharger/waterpump. But, I would've expected something a bit more catastrophic had the waterpump died?
I'm going to put the car in service mode this weekend so I can pull the radiator and get all the old coolant out of it so I'll have access to the front end of the car for inspections.

Any help is appreciated

 

 

If you've had a small leak for a long time that would probably explain it missing. I would pull the supercharger and water pump and check the 2 plates on the block behind them.

Do be careful with any components you remove as overheating makes the plastic very brittle.

I would consider a new water pump, thermostat and housing, and anything else that looks suspicious.

Change the oil in the supercharger and check the PTO gears while you're in there just to prevent future issues.

 

Pretty cool you have 230+K miles.

We're at similar miles with my kid's R53. The expansion tank started to leak from both cap and the seam. Unknown how old the tank was, but it was on there when we bought it 2+ years ago. Now with 233+K miles, no surprise that the tank was now showing it's age. We didn't have a catastrophic failure like yours, however, if we waited any longer, we would have. My guess is that when your engine temp went into the red, it boiled all coolant out of the tank due to the pressure loss from the seam and/or cap. That's probably where most of the missing coolant went.

After replacing the tank and tstat and housing, I'd also check the harmonic balancer to see if it's still intact. If that's broken, A/C won't work, waterpump won't pump, and voila, overheat in no time!

Let us know what you find.

 

Thats a good suggestion. I hadnt even though of that. The serpentine belt is still there, and looks reasonable. So the only failure from the balancer in order to create the overheating issue would be the belt slipping, no? I haven't noticed a dramatic drop in power that I'd think would come from the supercharger not spinning at its normal rate from the belt slipping. Plus, I was sitting in traffic at an onramp meter basically idling when it happened. I had always chocked the sudden lack of ac up to the car noticing something was wrong and turning the compressor off to remove load from the engine. I'll be sure to check it while I'm under the car, though. Thanks

 

An update:

Got the car apart, wasnt much coolant left in it. I went to swap the thermostat housing and the two coolant hoses that run into it are literally fused on. Not a huge deal, there wasnt any sign of coolant around the housing so I just swapped thermostats and gaskets into the old housing. I was following the TIS and had a vacuum coolant filler on hand so I figured I would know pretty quickly if there was a leak in the system. Put the cooling system back together and went to refill. Pulled the vacuum down to fill the system and no leaks, sweet. After about 10 seconds I realized I needed to turn the heat on and I still had the airbox out from doing the thermostat so no ecu. Maybe 2 minutes into putting the airbox back in to the car a leak pops up and the system instantly leaks down. From what I can tell, it sounds like its coming from the thermostat housing.

So far I've:
pulled, cleaned, and re torqued the housing
swapped the thermostat and gasket back to the old one
and done some dawning to try and find the leak (its a lot easier when air is coming out instead of going in)

Can't for the life of me find the leak. My only other theory is I somehow cracked the thermostat housing while it was under vacuum. The problem is, I cant replace the housing due to the hoses being stuck on.

Does anyone know where the hose on the exhaust manifold side of the thermostat housing goes? If it's not something outrageous, I'll just pull the housing out with hoses intact and replace the hoses.

 

Before giving up on removing the thermostat housing because of 'fused on' hoses, try to remove the hoses by first pushing them towards the housing rather than simply trying to pull them off which is what I suspect you are doing. Sometimes this simple maneuver is all it takes. Good luck.

 

I've had luck with that in the past and it was one of the first things I tried. Unfortunately, in my attempts to wiggle them about, I managed to snap the T junction that connects the reservoir vent line to the main coolant harness. I figured out where the lines terminate so I may just replace the entire thing since I now need 50 bucks in parts and the entire thing is only 135 to avoid breaking old plastic down the hose train.