engine temperature scale

[Welton]

My understanding is that coolant temp gauges on the dash are deliberately slow so as not to frighten the driver; if you saw the needle rise every time you went up a steep hill you'd think the headgasket was about to blow.

The gauge needle cam be slightly misleading depending on how you look at it i.e. you need to look at is straight-on at a 90 degree angle. That said you really need diagnostics to pic up the coolant temp and possibly also a laser thermometer on the hoses for confirmation.

[cheshired5]

Originally Posted by volvopilot

Could it be the coolant sensor being faulty or would that throw a code?

With a reading like you have so far, the coolant temperature sensor wouldn't be throwing a code.
Luckily with diagnostics, you can test the sensor quickly and easily.

[volvopilot]

thanks for all the replies so far.

The reason I am leaning towards a faulty sensor or ECU problems is that I don't experience any negative side affects of a faulty thermostat, like no heating, high idling and increased fuel consumption.

I am doing around 40 mpg with a 1.8L petrol which is pretty good
idle is around 700 rpm after +- 7 minutes

I have a simple diagnostic tool, is there a way to check the sensor or do you need more advanced computers?

[cheshired5]

Originally Posted by volvopilot

I have a simple diagnostic tool, is there a way to check the sensor or do you need more advanced computers?

A working sensor behaves a particular way so follow this video and see if yours does the same.

From the information so far, I'd say that your coolant sensor is fine.

[volvopilot]

I'll give that a try the next time I drive the car. thanks!

[Thassos]

Have a read of this thread, along similar lines, im wondering if a faulty thermostat can cause the engine coolant temp to take a long time to get from 70c up to 90c, the ford/mazda stat seems to have plastic bars that can break and cause a failure,

https://www.volvoforums.org.uk/showthread.php?t=280283

[volvopilot]

that is an interesting post and is pretty much my experience too.

from 70C it is reading dead center. Anything below 70 shows a slight deflection to the left. It reads full cold from around 50C

anything between 70C and 90C will read dead center. That is why you probably need OBD to diagnose a bad thermostat.

Mine is running 65-72C now. I have an appointment for a thermostat replacement next week. I was thinking about doing it my self but it is very hard to reach. I bought the car only 2 months ago so I figured it was a good idea to go back to the same place where I bought it from and maybe get a good discount on the repair since he sounded very fair when I bought it.

[Thassos]

It shouldnt be too difficult, have a look at the headlights on yours, do they have the quick release ford "tent peg" that makes it very easy to remove the headlamp unit, might give you better access. The main issue you might have is simply those sprung hose clips that are used on the big and small rubber hoses, but there are some inexpensive tools that get round that.., would be interested to hear how the coolant temp measures after the stat change... I would use volvo gen coolant (its a greenish colour) if your having it replaced, although you probably wont loose too much if you just do the stat.

[volvopilot]

thank you. I do have the quick release headlights and they are very easy to remove. It is still a little bit tight to get to the thermostat though. I am a little bit in doubt if I should do it myself, I might have time next week.

I will report back the ECT readings and hopefully this will be the fix. It should read 85-90C according to my research.

[Thassos]

Hi volvopilot,

any progress with your thermostat replacement?, do you find the coolant temp eventually gets to 90c ? , or never more than 70c ?