Odd coolant issue

[rexemper]

Hi

Having an odd issue with the coolant light / warning system in the SL over the last few days. Initially the coolant light came on with a “visit workshop” message. So I let the car cool down and checked the level - seemed ok.

Didn’t drive it for a couple of days after that, but when I did I noticed that the coolant message appeared to start with and then disappeared. Seemed to be as the car got up to temperature it went away.

Drove into work this morning and noticed that the same thing happened with the message - was there initially and then went away. But I also noticed that when I braked the message would come back. At the same time the temperature gauge would drop to just above 80C. As I drove again, the message would disappear and the gauge would go back to 90C. At no time has the gauge gone above 90C.

I’ll check the level of the coolant again, but this just seems a bit odd so thought I’d see if anyone has any advice on anything else to check?

Whilst I’m here, where should the coolant level be when the car is cold? The manual is not particularly clear.

Thanks

 

[bembo449]

if your levels are all ok everytime you check it , id say its a duff sensor , had plenty of these on other makes especially VW's

 

[alexanderfoti]

RE the level, it should reach the black plastic section inside the header tank.

 

[rexemper]

if your levels are all ok everytime you check it , id say its a duff sensor , had plenty of these on other makes especially VW's

RE the level, it should reach the black plastic section inside the header tank.

Thanks. On the way home this evening it was a bit different - it showed the coolant message while it got up to temperature and the stayed at 90C as before. Then as I hit slow moving traffic the gauge went up and up. But then strangely it would go down and then quickly bounce up again - it would typically drop down to around 90-95C and then bounce back up. It was touch and go as it was almost at the limit at one point, but managed to nurse it home.

Checked the heater and turning the dials up it got the car nice and hot inside.

Anyway, its at home now so will let it cool down and then check the levels in the morning.

If it is a duff sensor, are they difficult to change (and how much are they)?

Any other ideas based on the drive home this evening?

Cheers

 

[bembo449]

right , based on this new evidence im wondering if the stat has broken down and is flipping around in its housing ?? ive not seen it on MB cars before but never say never , did you check to see if the coolant system had pressurised ??

 

[rexemper]

right , based on this new evidence im wondering if the stat has broken down and is flipping around in its housing ?? ive not seen it on MB cars before but never say never , did you check to see if the coolant system had pressurised ??

what do you mean by pressurised?

 

[sonic]

right , based on this new evidence im wondering if the stat has broken down and is flipping around in its housing ?? ive not seen it on MB cars before but never say never , did you check to see if the coolant system had pressurised ??

A favourite with the old MK1 Mini of the 60's.

 

[LostKiwi]

Squeeze the top radiator hose. If it's rock hard the system is pressurised.

 

[rexemper]

ah ok. can do that while its hot or cold, yes?

 

[LostKiwi]

Hot. No point when cold. Also preferably engine running.

 

[rexemper]

will have a look now...just had a look and the hose is not rock hard but its definitely got pressure inside, just gives a little when you squeeze. Fan is running fine too as it kicked in while I was having a look.

 

[bembo449]

hmmm

 

[LostKiwi]

will have a look now...just had a look and the hose is not rock hard but its definitely got pressure inside, just gives a little when you squeeze. Fan is running fine too as it kicked in while I was having a look.

It should feel pretty similar to squeezing a tube of toothpaste.

 

[rexemper]

It should feel pretty similar to squeezing a tube of toothpaste.

That is pretty much how it was. I'll check the level again tomorrow and see what I find...

 

[rexemper]

Well that was odd - checked the coolant level today and it was pretty much exactly right - to the top of the transparent part/bottom of the black part.
There are two thin hoses that come out of the black section, held in with metal clips, I removed those and cleaned the ends with tissue and put them back in - more because I took them out than for any other reason.

Anyway, started the car, no coolant level warnings. Let it idle for a few minutes, no coolant warnings. Took for a ten minute drive and no warnings. Temp rose steadily and held rock solid at 90C. Checked pressure in the top hose - fine.

I'm tempted to remove the temperature sensor to clean it - how do I do that?

So now what???

 

[mattkh]

If the coolant was replaced recently. then there may be some trapped air.
Secondly, I would clean/check the electrical wires to the temperature sensor.

 

[rexemper]

If the coolant was replaced recently. then there may be some trapped air.
Secondly, I would clean/check the electrical wires to the temperature sensor.

No, coolant hasn't been changed for a while. How do I check and clean the wires to the sensor? I know how to check and clean, but where is the sensor is what I meant?

 

[bembo449]

I think you need to do the checks you did in the earlier post , after ! you see the gauge doing its little dance and if after that all is well , just replace the coolant sensor

 

[rexemper]

I think you need to do the checks you did in the earlier post , after ! you see the gauge doing its little dance and if after that all is well , just replace the coolant sensor

Just been out for a longer drive and sure enough, after about 15 minutes the coolant message came on. The temp display dropped to just about 80C and then went up again to 90C. Settled down for a while and then just kept going from just over 80c to 90C with the coolant message flashing.

Came home and left the engine running, here's what I found/checked:

- System was pressurised - main hose nice and firm
- Fan wasn't running
- As I left it idling for a few minutes, the temp climbed to 100C

Turned the car off and then a couple of minutes later, switched t back on. Same checks, except this time the fan came on straight away.

Can't check the level of the coolant yet, but will do. Suspect it will be fine.

Does this point to the thermostat not working properly seeing as the fan didn't cut in?

Also, one other thing to check is the fuse(s) for the system - anyone know which one handles this?

Thanks

 

[alexanderfoti]

I have just re-read this thread.

Coolant, check level - refers to the level in the header tank.

Coolant, visit workshop - this normally indicates an issue with the fan or the fan controller.

As you are getting the latter, and your temperature goes up without the fan kicking in, I would suspect this is your issue.