BMW 630i (N52) Thermostat behaviour

[gipized81]

Hello all!

I have a BMW 630i that is doing some odd things from cold start.

I've got into the 'hidden menu' on the instrument cluster and have been keeping an eye on the coolant temperature from cold start. In a nutshell it heats up very quickly up to 120'c when the 'engine too warm' warning pops up. After a bit, the cabin heating suddenly gets warm and the coolant temperature drops by 30'c.

What do you reckon? New thermostat?

[DaveZed]

If it's the N52 engine, isn't it more likely to be the well-known issue of the Pierburg variable speed electric coolant pump on its way out? Good idea to replace the thermostat too, if you replace the pump. What is the mileage on it? Pump failure is apparently quite common around 60-100 000 miles.

[gipized81]

It's on 101,500 at the moment. I did wonder about the pump, but once 'something' switches and the heat starts to flow all is well. Could it be the pump not firing up when it's supposed to possibly..?

[Touring442]

The pump is on its way out. They're not so dear now, 2-300 quid plus fitting. Replace the stat as well.

[DaveZed]

Have you scanned for codes? When the pump started packing up in my E90 330i it threw a code with a description along the lines of "Coolant pump speed deviation". I don't recall the specific numeric code. The only symptoms I had noticed were that the radiator fan was noisy/running more than usual when in traffic. One of the reasons for the electric pump is to allow more rapid heating of the engine from cold, so it likely could have something to do with the control around that, yes.

[gipized81]

I scanned for codes the other week for another unrelated thing but didn't see any nasties relating to cooling. It makes sense to change both the pump and thermostat at the same time I suppose. Just didn't want to 'fix' something that isn't necessarily broken!

Thanks for the comments all!