Good morning everyone,

Was driving home with newly purchased 2008 MCS Sidewalk with 97k miles when halfway during the 80mi trip back home the car started overheating and hot air stopped blowing out the vents so I had to pull over and park the car to cool off for a good 20-30mins. Restarted it, hopped back on the highway and within 5 mins the temps crept back up so I pulled over for good.

I will return in a couple hours and start by bypassing the heater core and see if that does it. That would be best case scenario and would save me a hefty tow bill. However I am prepared for the worst and was wondering if anyone here had experienced the same issue?

Been thinking and it could also be as simple as air introduced into lines, water pump failure, stuck thermostat, or the dreaded water pump supercharger drive.

If the bypass doesnt do the trick then I'll be busy troubleshooting instead of getting to drive..

What do you guys think?

Thanks for your time and help.

 

I've read this post a few times, still not sure I understand the situation. It's days later since you posted, and hopefully you've resolved the problem, but in case you didn't:
Do you mean it started blowing out the vents, like maybe you were running the AC and it suddenly stopped working?
Does what? It isn't clear how/why the heater could be at the center of your overheating issue UNLESS it's leaking, rather badly. Seems like you would have coolant leaking inside the cabin though.

Or some combination of those.

Could also be the radiator fan stopped working, either because the motor or the fan switch failed, or the expansion tank and/or cap blew, system lost pressure and you've been leaking coolant, to the point you may have run out of it. Good discussion of the fan system operations in question #30 of 1st Gen FAQ which you can find HERE.

Should start with the basics though - coolant level, serpentine belt and tensioner, any obvious leaks. Check for OBDII codes. Check charging voltage at idle (alternator) and listen for unusual noises.

Did you get any other symptoms - like a burning rubber smell (failed crankshaft pulley) or the car went into limp mode?

 

Mine was a split in the seam of the expansion tank. I got the car to work and noticed a little smoke coming from the hood scoop, I had just parked at work and my heat went cold. So I had my buddy run me up to orielly’s we picked up so g48 and I filled it up while I had just started the car, filled coolant up to fill and drove home, 8 miles was on highway at 65 with cruise set, tired my best not to put a load on it. Then parked it till I could get into mechanic, filled it again, and drove 2 miles to mechanic all 25-35. When they pressurized the tank that was when they found coolant coming out of the seam. Luckily this happened in December and I have had no issues since tank replacement.

 

Update everyone:



Low and high speed fans have always worked from the get go and I bled cooling system properly on day one. Thermostat opened up perfectly at 195, confirmed with boiling water and a thermometer alongside a brand new replacement.



Low compression on Cyl 1 & 2 made me suspect the head gasket because the tops of the pistons looked to have been steam cleaned by the coolant and after dropping a bit of oil in the cylinders smoke escaped from the engine and out of the bay upon combusting so I pressurized the cooling system and let it idle. The gauge showed increased pressure and eventually the tank burst at the seam. At this point I decided to pull the head and confirmed a blown gasket. Cyl 1&2 had small cracks going from the spark plug holes to the valves as well.



I removed the water pump and there was a dried up corroded waterfall of coolant at the inlet where it mates with the block. The impellers were still intact but when turning the small water pump drive(that mates to the SC) by hand it was really stiff but not completely locked, also rusting so coolant may have been leaking out of there too.. There were no blockages of any kind in the coolant system or radiator so I'm assuming pump failure or PO failed to keep coolant level adequate so it overheated on them before me.



Anyways, I have abused head and a new water pump w metal impeller along with new supercharger oil going in tomorrow. Pulling off the supercharger to inspect the dog gear that drives the water pump to make sure that didn't fail.. Do I just unbolt the rear section, open up and have a look? Or are the parts prone to popping out or must stay in a certain position?



Thanks for reading