1999 S80 Intermittent fault with engine temp warning

rTiGd2 · Post by **rTiGd2** » 05 Jun 2014, 00:22

So I have this rather interesting (and now more annoying than worrying) problem with the coolant temperature gauge. Reproducing it isn't easy but tends to be a case of letting the car sit at idle for about 5-10 minutes while touching nothing.

What happens is, well, the gauge reads as if a thermonuclear event just happened in the engine. It goes from a normal running temperature, to the needle attempting to escape stage right, with the dash warning to stop and shut down.

Yet, it isn't. The radiator fan is running (overtime, but comfortingly) and all is well. There appears to be pressure in the top hose and it isn't overly hot.

After this happens I can leave the car switched off for 24 hours or more and when I come back, gauge is still at high and it takes a few minutes of running for it to back down. Try to run within about 5-6 hours generally doesn't reset the problem.

This said, two things have also been at fault with the car. The front lambda sensor was fitted with a turbo version (this is a 2.4 N/A engine) and the heater on it wasn't working, so always had a lambda sensor light (which, stupidly, we lived with as was warned it could be an ECU replacement, dirty dealers!) and I only thought to change this out (it was new 2 years ago) with a Denso, which fixed the problem (the original was a Bosch generic, fitted by my local garage who, in all fairness, never touch Volvo.)

The other fault is a blocked PCV, which is getting replaced this week.

Since the lambda sensor change, the car was run at idle for quite some time before the emissions re-test and the gauge never shot up (which can happen with this fault anyway) but it makes me wonder if anyone has seen this problem before and/or perhaps have a theory if it is linked to the lambda sensor fault/PCV clogging?

A final note, there are no codes being thrown and a meter test of the coolant sensor (I didn't run this, the local garage did, so I'm assuming they tested the correct sensor, in the correct way) showed it to be working, while the fault was there. Taking the sensor lead off didn't correct the error (I never did check if the dash gauge went flat when it was off.)

Kindest regards for reading and in advance for any theories, Tig.

rTiGd2 · Post by **rTiGd2** » 09 Jun 2014, 15:15

Is there a more general board to post this query on? I'm guessing it probably not limited to just a possible S80.

Post by **Oly_850** » 09 Jun 2014, 18:45

I've seen odd things like this happen with wonky thermostats, even though the engine isn't actually over heating. Is the car losing coolant? Any air bubbles coming up through the coolant tank?

rTiGd2 · Post by **rTiGd2** » 09 Jun 2014, 21:02

Coolant is at the same level it was since a major dealer service two years ago. Coolant temp is actually low, because it keeps the fan running all the time (guess I'll be replacing that before too long if I can't track this problem down.) No bubbles in the coolant reservoir, the pressure seems fine and no tell-tale sounds of air in the system anywhere.

Post by **Oly_850** » 09 Jun 2014, 21:17

Although it bothers me to suggest it, I'd do two things in this case:

Coolant temp sensor
Thermostat

They're in the same housing and relatively cheap. Get new gaskets too.

Post by **jimmy57** » 09 Jun 2014, 22:26

Part of what drives this is the "lying coolant gauge" feature that so many car makers and Volvo use. The temp gauge will show no needle activity for coolant temp between upper 80's C to almost, if not, 110C. SO things can be happening and when the temp exceeds that upper limit of "normal" then the system moves gauge aggressively. What I am saying is that it may be running warmer than you think when the gauge stays in middle and a few degrees more and you get the message and full gauge needle reading

difflock54 · Post by **difflock54** » 11 Jun 2014, 18:07

Which fan is running all the time?
The AC fan will run if the AC is switched on but the radiator cooling fan should not be on all the time.
Temp sensor / thermostat are the likely candidates.

rTiGd2 · Post by **rTiGd2** » 16 Jun 2014, 01:13

Interesting thoughts, now I'm not too certain if they checked the thermostat, or the temp sensor.

Just to 'mix things up' a little, since changing the front Lambda sensor (the same garage fitted a generic one for the turbo model, rather than the N/A version) I don't appear to have this problem arising. Perhaps that's a false negative and it's just a matter of time, or did I stumble upon another interesting quirk of my belo(ath)ved car?

rTiGd2 · Post by **rTiGd2** » 16 Jun 2014, 01:16

difflock54 wrote:Which fan is running all the time?
The AC fan will run if the AC is switched on but the radiator cooling fan should not be on all the time.
Temp sensor / thermostat are the likely candidates.

The radiator cooling fan, once that gauge tries to wrap itself against the right stop. It does stop, eventually, when the ignition is off but once I turn the ignition back on, and the gauge is still showing max, the fan triggers, even the next morning until it's started and the needle decides it's not actually 10,000,000 degrees any longer.

What is interesting is that once this happens, there appears to be a certain number of hours before things go normal again. It doesn't matter how cold the engine is. I've even had it where it happened at around 22:00 and was still high at 11:00 the next morning but didn't reset until driven for about 30 minutes.

Personally, I think the car is just trolling me (the Swedish sense of humour is like that)

rTiGd2 · Post by **rTiGd2** » 17 Jun 2014, 12:11

Oly_850 wrote:Although it bothers me to suggest it, I'd do two things in this case:

Coolant temp sensor
Thermostat

They're in the same housing and relatively cheap. Get new gaskets too.

Well, it did it again after sat for 8 minutes idle, so I'm going to have to find the sensor and thermostat, then figure out how to change them. Thank you for the advice.