[Eddamoo]

So winter is approaching for us northern hemisphere folk. I'm seeing lots of threads on the forum regarding slow warm-up of our diesel engines. I would love to know if anyone has modified the coolant system to improve this? Ive tinkered with cars for years and often played around with basic coolant systems but this one needs a bit more research!

I recently tried to diagnose a slightly slow warm-up of my 430d (https://f30.bimmerpost.com/forums/sh....php?t=1763280) - what i realized was that despite the thermostat being closed, a lot of hot coolant was still working its way into the radiator.

After 20 mins slow/fast idle it hit 76C Coolant/75C Oil Temp in 12C ambient:
Hose FROM engine block under inlet manifold = HOT
Right side of Radiator = HOT
Left side of Radiator = Warm
Left side return to Thermostat and Water Pump hose = Cold

On my previous (VW) diesels, both coolant hoses and the rad would be stone cold until the Thermostat opened, which indicates to me that our engines have a slight design flaw.

The heat bleed is coming from the block through pipe #1 in the diagram. My thoughts would be that an in-line thermostat with a conservative opening temp (~80C) in that pipe could significantly shorten warm-up time. The only problem would be the return hose to the expansion tank (
#3) and im unsure if blocking this path until warm would have a negative effect.



It'd be great if someone could validate my findings with their engines

[thewird]

Hi there, did you ever solve your issue? I have an F15 with the DPF deleted but everything else in place and the engine refuses to get up to temperature in winter temperatures. I have changed the thermostat twice now with a brand new BMW one and the issue persists. Just driving normal the coolant/oil temperature will hover around 40-50 degrees. If I sit at high idle, it eventually gets to operating temperature.

thewird