1998 S70 Overheating

[abscate]

Is the system pressurising ok? Carefully crack the cap before it gets hot to see if the system is closed to atmosphere. It needs to be.

The other area to consider is the water pump. The impeller can break up on these cars, and then you have no coolant flow and it will quickly overheat at revs. Thats a big job as the water pump is driven by the timing belt.

[sourcaffeine]

Is the system pressurising ok? Carefully crack the cap before it gets hot to see if the system is closed to atmosphere. It needs to be.

The other area to consider is the water pump. The impeller can break up on these cars, and then you have no coolant flow and it will quickly overheat at revs. Thats a big job as the water pump is driven by the timing belt.

The system is pressurizing. If I crack the cap, it hisses air. If I open more within several hours of it having run, it will spit come coolant out.

I am not afraid to change the water pump, although the previous owner claims he did that not long ago. The timing belt looks new, so I am inclined to believed he did in fact change it when he did the belts.

[precopster]

Start with a thermostat. They often stick closed and for $25 that's cheap peace of mind. Get a Stant Xact which is a Wahler OEM or just a Wahler boxed one.

Next is the ECT. Get a genuine one. It sits on the thermostat housing.

[tryingbe]

Test the coolant system for exhaust gas.

[erikv11]

Test the coolant system for exhaust gas.

Ding, ding, ding!

[JRL]

When I say it was rising, it was a single notch or so, and returned to normal a few seconds later.

I will repeat, the gauge should not move even the teeniest bit when up to operating temp, not "even a notch or two", NO MOVEMENT WHATSOEVER.

[sourcaffeine]

Test the coolant system for exhaust gas.

Purchased a block tester, and according to the test, there is no blown head gasket.

[erikv11]

Well, maybe frustrating because of the cost of the test but still that's good news.

So to make sure I am following:
- the basic symptom is an erratic gauge, right?
- you have swapped the t-stat, bypassed the heater core, and tested for exhaust gases in the coolant.

Is it possible the actual temp is not rising, rather the ECT sensor is screwy? They are a common failure item. With a faulty sensor, fuel economy might be taking a hit too. You can test the resistance of the sensor at different temps, very simple test, if you search you will find the ohm values have been posted in the forums here many times. Maybe that test is even in the repair database. I think that is what I would do next.

[sourcaffeine]

Well, maybe frustrating because of the cost of the test but still that's good news.

So to make sure I am following:
- the basic symptom is an erratic gauge, right?
- you have swapped the t-stat, bypassed the heater core, and tested for exhaust gases in the coolant.

Is it possible the actual temp is not rising, rather the ECT sensor is screwy? They are a common failure item. With a faulty sensor, fuel economy might be taking a hit too. You can test the resistance of the sensor at different temps, very simple test, if you search you will find the ohm values have been posted in the forums here many times. Maybe that test is even in the repair database. I think that is what I would do next.

I will pull out my meter and check it.

Although it would surprise me. The gauge is erratic, but only after it's reached operating temperature for a while. If I rev up to 2,500RPM it will end up reaching operating temperature and after a minute or two, the gauge climbs. Then it will go up and down until it starts to run too warm for me to be comfortable with.

[sourcaffeine]

While this probably isn't relevant to the overheating, I noticed on the passenger side, between the front and rear seat under the car there is a gash/hole and coolant is very slowly leaking there. Probably a single drop every few seconds . I don't see any hoses, and it almost seems to be coming from between the metal underside and the vinyl covering.

I wiped it with a paper towel, and it builds back up, but it is from a small spot and I cannot see a source. Any idea where this might be from?

Edit: I am inclined to think it is left over coolant from the heater core, as I have not yet removed the heater core and it looks like straight coolant.

Edit: I have been broken and have now decided to scrap the car. I can't figure out the problem, and it is not worth my time. Thank you all for your help, I just can't spend any more time/money on it.