99 Volvo v70

RB3 · Post by **RB3** » 10 Aug 2026, 12:13

okay, change the oil over the weekend. I went from 5W30 to 5W40 as we've had a lot of heat and the car is getting up in mileage. got in this morning drove A very short distance and when I got back in the car it did not want to start. It started on the second or third try but check engine light will not turn off after driving . ran codes at local auto parts store indicates coolant temp sensor and thermostat. both of these were replaced back in March. any correlation with the oil change? vehicle is running ok and at normal temp. fluids are okay. inspected for any oil leaks after the oil change and a couple of times since including now. Help!
FYI I'm still using green coolant because that's what she's raised on.

Update:
On my way back from auto parts store temp gauge was fluctuating. Thermostat is under warranty but it's only been 4 months

. Sensor/ thermostat shouldn't even have been touched removing the oil cap. I did repair electrical in the tailgate i.e. the ground But that shouldn't affect anything either. I guess it could just be a bad part

aeg · Post by **aeg** » 10 Aug 2026, 18:09

ECT itself may be the problem, but check the wiring/connector near the ECT.

If the ECT signal is not valid, the car will not increase the fuel mix while starting, resulting in hard starts. It's possible you may have bumped the wiring while changing the oil.

I believe after you replace the ECT or fix any wiring problem, you will need to clear the code before starts will return to normal.

RB3 · Post by **RB3** » 10 Aug 2026, 20:12

Thanks, visually inspected the plug. It's likely the original. But now I recall needing the sensor in a hurry last time and picked up a cheap aftermarket telling myself I would upgrade in the near future. Lesson learned. can't mess around with sensors. especially on these cars. So still have to wait for an original part. They sure don't make 'em like they used to.

Post by **abscate** » 11 Aug 2026, 01:56

The 1999 plug doesnt break like the -1998 version.

But if you didnt use a Volvo ECT that aftermarket life of 6 months is about right. Its a mission critical part and the resistance map on the aftermarket ones isnt good.

RB3 · Post by **RB3** » 11 Aug 2026, 13:32

Got an OEM ordered. Now need the thermostat as well.

is the green coolant still okay? I used O'Reilly's Green 50/50 mix. probably hasn't been flushed in a few years.

What do you think about the 5W40 recent switch from, 5W30?
where do you source your OEM parts? I suppose the junkyard can be useful for some things, but do you go straight to the dealers? IPD is so so

RB3 · Post by **RB3** » 11 Aug 2026, 13:45

That plug/wiring is quite precarious just dangling down past the alternator. Gotta laugh at these cars sometimes.

Post by **Olegs855R** » 11 Aug 2026, 17:53

SOMETIMES???

RB3 · Post by **RB3** » 13 Aug 2026, 16:15

Got a Mahle Thermostat. It was the quickest + It does say it's OEM
Made in Czech Republic
Mahle Aftermarket address in Stuttgart, Germany

There's no bleed hole. I see FCP has Volvo listed ones
claiming OEM as well. do they come with the holes anymore? do I need to go straight to a dealer? If and when I do a flush I'm inclined to stick with the 50/50 green. What is the general consensus here?

Post by **abscate** » 14 Aug 2026, 06:16

RB3 wrote: 13 Aug 2026, 16:15 Got a Mahle Thermostat. It was the quickest + It does say it's OEM
Made in Czech Republic
Mahle Aftermarket address in Stuttgart, Germany

There's no bleed hole. I see FCP has Volvo listed ones
claiming OEM as well. do they come with the holes anymore? do I need to go straight to a dealer? If and when I do a flush I'm inclined to stick with the 50/50 green. What is the general consensus here?

I use the Volvo coolant but pretty much any will do as long as its changed out (I do 3 years/30,000 miles)

Mahle for the thermostat is fine. The ECT (temperature sensor) should come from VOlvo, or as we say here, from Mother.