Things you discover #387 - Cooling system on an E46 B3S

[Charles]

Just been chatting with Phil Crouch because I was concerned that something was amiss with the cooling system on my car.

Had a situation last week stuck in traffic when the dash gauge starting heading north from normal. I switched the Dynavin to the OBD setting and the coolant temperature had just gone to 116C. I started to get worried and then it started falling again back to mid 90s. The following day and then both days this week, I've been doing the normal commute with the OBD display on to monitor what is happening as I thought that the electric fan was playing up. Steady state on light throttle and the temperature was holding at 95/96C but under load it drops to 88C before returning to 95/96 under light load.

It transpires that this is perfectly normal for my car. I have an 88C thermostat but when the car is running at gentle steady state on the motorway, the EMU chooses to increase coolant temp to 95/96 to improve emissions. Under load the EMU increases cooling and the temperature drops to 88C. If the car is not moving, the top end of the normal operating range for my engine is 115C, after which the cooling fan will kick in to stop it going any higher when stuck in heavy traffic.

Based on this, it appears that everything is doing exactly what it should - but now I know why!

[hashluck]

Yes, I remember going through similar on an E60 which I am sure from memory had two thermostats, one for the gearbox cooler, and it was fun and games tracking the temperatures, I was surprised at how hot modern engines can and are allowed to/supposed to run for best efficiency.

[Bob]

Interesting to know Charles.

Surprised you haven't noted this particular situation in the past, it's not like you use it sparingly is it?! Or have you just never enquired about it any further?

[Charles]

Surprised you haven't noted this particular situation in the past, it's not like you use it sparingly is it?! Or have you just never enquired about it any further?

Fair question, Bob. Normally I don't see the dash gauge rising when stuck in traffic, so when it did last Thursday it was unusual and suggested a problem - hence why I switched on the OBD feature to see what was happening (along with the subsequent monitoring).

Interestingly, my commute this morning was "light touch" and I had a 95/96C steady state. However, this evening's commute was more spirited and the OBD temp was 88-90 for most of the journey home which appeared to confirm the explanation that Phil gave me yesterday. Still planning some further monitoring over the next week or so to satisfy my concerns and curiosity.

[BarryM]

Very interesting, the M62 is generally known as the engine that runs ridiculously hot at around 106 degrees but I've not heard of one running at 116 degrees. As we know many people including owners on here have fitted an 88 degree thermostat to lower the running temp, however I've doggedly stuck with the original thermostat and the intravee allows me to monitor the actual temp in a similar way to your Dynavin.

Ironically I was sitting in a traffic jam @ midnight on Saturday for 15mins and the temp started to rise to 108 degrees which is higher than normal and then 109. The intravee has a temperature alarm option (manually set at 109 degrees by me) and I got an overheating warning on my OBD which had me panicking, turned the engine off as we still weren't moving and temp dropped and I got home safely but I'm inclined to think my thermostat might have failed as I've never seen 109 in all the years I've owned the car. I will start another thread if I find a problem with my engine but haven't got much spare time right now to plug in the computer to see what codes I might have.

[Charles]

Bit of an update on this one - it transpires that the electric fan has failed and the AC condenser is heavily coated with road grime, thus reducing airflow through the radiator.

A new fan and condenser later and my temperature rises to a maximum of 98C when hot and stationary.