Bit baffled after changing thermostat!

Post Mon Apr 02, 2012 1:04 pm

Original post: Hi folks, my car just failed it's MOT on high emissions among other things. It was the first time I have driven it since bringing it home last year and have noticed the engine doesn't seem to get up to temperature. The needle sits at about a quarter. I'm wondering if a knackered thermostat could be linked to the high emissions? I don't think it is idling too high! [/list]

Added info: Ok changed the thermostat and the temp guage still not going above 1/4! Have just read a post that this might actually be normal depending on what the temp rating is on the thermostat.

The engine gets hot, the top hose gets very hot, the hose from thermostat housing to the bottom of the radiator stays quite cool.

I'm still quite concerned about it, any thoughts?

Post Mon Apr 02, 2012 2:42 pm

Have recently had the same issue...overcooling and not getting much above 1/4 of the way up temp gauge.

Was advised by a few on the zone that it was most likely a thermostat fault. Changed the thermo and housing as bolts sheared when trying to remove and has solved the problem. If therm is faultly will be using additional fuel to compensate for cold running. This could be the cause of the high emissions but as a thermo is about £20 would be worth a try first.

Post Mon Apr 02, 2012 2:43 pm

The cold start injector could be constantly open as the blue coolant sensor is giving an incorrect reading, thinking the car is constantly cold.

The blue coolant sensor is really cheap, and very easy to change. I'd start with that.

_mcbonio

Post Mon Apr 02, 2012 2:49 pm

the blue sensor isn't giving an incorrect reading, the engine is actually cold from the overcooling. Thermostat is the place to begin.

Post Mon Apr 02, 2012 6:04 pm

Jos wrote:the blue sensor isn't giving an incorrect reading, the engine is actually cold from the overcooling. Thermostat is the place to begin.

This is the right advice......

Post Fri Apr 06, 2012 3:20 pm

Ok changed the thermostat and the temp guage still not going above 1/4! Have just read a post that this might actually be normal depending on what the temp rating is on the thermostat.

The engine gets hot, the top hose gets very hot, the hose from thermostat housing to the bottom of the radiator stays quite cool.

I'm still quite concerned about it, any thoughts?

Post Fri Apr 06, 2012 4:55 pm

Did you replace with new therm or used one? Did you check the one you have put in was working prior to changing? Your right when you say there are different temp rated therms so check you've used the correct rated.

Post Fri Apr 06, 2012 5:17 pm

The diffrenct between quarter and half from memory is approx 3 or 4 degrees if you are worried change the blue temp sensor but if th car is not overheating all is well.

the high emmisons can be caused by the temp sensor telling ECU its colder than it is but did they let it warm up properly before testing ?
HTH

Post Fri Apr 06, 2012 5:46 pm

See my post here: http://www.e30zone.net/modules.php?name ... c&t=217897

Ben

Post Fri Apr 06, 2012 6:09 pm

Have you fitted the correct temperature thermostat?

Post Fri Apr 06, 2012 6:12 pm

If the correct thermostat (80 degrees C for a 325i) is fitted the gauge will show just over a quarter at normal running temperature.

I don't think there is anything wrong with Jimf's thermostat.

Ben

Post Fri Apr 06, 2012 6:32 pm

I have used a known working thermostat from a '94 520i that I am breaking. RealOEM says it is the same part number. It was only in the car six months so happy to use it.

Well I think I am quite happy that all is well with the cooling system. working thermostat, new coolant, No overheating, the needle seems to be happy at 1/4 and this seems normal from what i'm reading today.

The car is idling steadily at about 650rpm.

Need to have another think about what is causing the high emmissions!

Thanks for all help guy, always appreciated.