Coolant Issues

[jmarinara]

I own a 2000 s40 1.9L Turbo.

At the end of summer, I replaced my plugs and wires and noticed that the engine seemed to be running hot. A check engine light came on revealing I needed a new temp sensor. A friend suggested that I take out my thermostat in the meantime to attempt to cool the engine which I did. After tracking down the right part, I replaced the temp sensor and put the thermostat back in place.

That's when my problems began. For one thing, I had no heat in the cabin. It was as if my thermostat was never put back. Also, I noticed that coolant was leaking around the "lid" where the thermostat belongs. I replaced the bolts and played with the tightening and loosening of them to no avail. It's as if the "lid" won't seal. I should note here that it feels like the threads need rethreaded when I put one of the bolts in. I can't really get it to tighten all the way. It keeps turning, albeit snuggly, without fully tightening. I may try a shorter bolt.

After a few days, the car began to overheat. I reasoned that the anti-freeze was leaking and eventually there was simply nothing to cool the engine with. I refilled the system and it seemed to fix it. However, I continue to have issues with heating my cabin and with the temperature of my engine. Here's what I find odd: If I turn the heat on in the cabin, the temp in the engine spikes high. This is especially true if I use the "auto" feature to heat the cabin.

I suspect that the problem would be fixed if I could get the coolant leak under control. Does anyone have any ideas on how to make it seal properly? However, I speculate that I may have another issue, such as the need for a new thermostat, or perhaps a leak elsewhere. Does anyone out there have any ideas?

Thanks in advance for the help.

[FlyingVolvo]

When you replaced the ECT sensor, did you use a Genuine OEM one? Any aftermarket ones will likely cause you trouble down the road. A funky or bad ECT sensor cannot really overheat an engine, as all it does it report the temperature to adjust the efficiency of the engine, but it may also report weird readings.

As for the coolant itself, that definitely is another issue. Check all the hoses for leaks after a drive. Anything dripping on the ground? Check under your driver's side carpet, any wetness?

I would definitely replace the thermostat. Use a Wahler or one from Volvo. Make sure it has the round black gasket around the edge of the thermostat. It will leak badly if this is either not in place or deteriorated. Aside from leaks, replacing the thermostat and ECT sensor with good GENUINE parts, will solve most people's problems.