W204 replaced thermostat - still got CEL

[MancMike]

Hi, all.

I know the ultimate solution would be to get it on star, and I'll do so if it comes to it, but I'm wanting advice from others before I resort to that.

I've been having the problem where it takes forever for the engine to get up to temperature, like 15 miles, and if I then hit the open motorway, the engine would actually cool somewhat.

I replaced the thermostat tonight, and went for a drive and the engine got up to temperature much faster, like normal if not better.

The CEL is still lit though. Does it need to have a few fully cold warm ups to notice it's fixed?

Thanks.

 

[Yugguy]

I never had any lights when my thermo was dodgy.

 

[daveenty]

I never had any lights when my thermo was dodgy.

This really.

As you infer in your original post, if you have a warning light then it needs reading to determine what's causing it, but I wouldn't have though that a faulty thermostat would be the culprit.

 

[zipdip]

Have you not got any sort of diagnostic scanner,£40 buys you a decent one,of course it is not a Star but it would reset fault lights ,imho one of these is vital if owning a merc.

 

[MancMike]

I've got two, a wifi one that connects to DashCommand app, and a £15 handheld one.

Neither will connect. Says error in connecting.

The good news though is that the engine was up to 80°C after just over 2 miles and hit 90°C after just 3 miles. With the old thermostat, it wouldn't be at 80°C after 10 miles and wouldn't hit 90°C after I arrive 13 miles total, and it was a bit colder this morning than it has been the last few mornings too.

Fuel economy is back up to normal too.

I've read others' saying that they had thermostat related codes read, which after replacing the 'stat didn't go, but after a couple of cold starts it did, so I'll hold out a day or so longer before booking it in. The ODBii not connecting is worrying though. It powers the device, just can't connect.

 

[zipdip]

Well good news about the car temperature and fuel consumption back to normal,but I would get the ecu connection looked at,something wrong there,and it is the only way to find out what is going on with the car.

 

[DSM10000]

Any local garage will have a code reader you can try.

A CEL is not uncommon if the thermostat fails, the ECU expects a certain water temperature after a certain period of running, if these parameters are not met then a CEL may be triggered.

I have had this on other cars, notably a Saab 9-5.

 

[Auto-mobile]

Your engine does put on a warning light for thermostat, you will probably find this needs to be reset after replacement, if you have a different engine to the op chances are your engine doesn't throw a code for thermostat.

 

[MancMike]

So I was right to wait a lil'.

The check engine light went out this morning and hasn't been back, so clearly the car is happy with the new thermostat, as am I. :bannana: