1995 850t overheating

[styls]

Had to change the heating core, after that car keeps overheating. runs for awhile then gauge starts to rise and fall. changed the thermostat, results the same.

Thanks for your help.

[Baptiste1106]

Have you done a compression test? Water pump? Pressure test for leaks? Block test for head gasket?

[timmybdaddyof3]

What is happening when it overheats?
think - at idle, when accelerating, etc.
If you don't have the tools to pressure test etc. as listed above try some of the basics - coolant in oil or vice versa, does the exhaust smell like coolant, and does the radiator actually get hot when the car is running (majority of its surface area will be at ~190*F when at operating temp.
Let us know your findings

[erikv11]

Rising and falling temp gauge also makes me think of these two things:

- partial blockage somewhere in the cooling system (most likely)
- bad ECT sensor

You can check the resistance of the ECT sensor. From https://www.matthewsvolvosite.com/forums ... hp?t=11429:
ENGINE COOLANT TEMPERATURE SENSOR RESISTANCE TABLE
Temperature ˚F (˚C) ............................Ohms
32 (0) .............................................. 7300
68 (20) ............................................ 2800
176 (80) ............................................. 300
212 (100) ............................................ 150

Very easy to check 0 (ice water), 68 (ambient) and 212 (boiling water).