Thermostat good or bad?

[MartinN]

Hi and some help plse.
I have a year 2000 2.0 ltr. Runs fine but didn't warm up too quickly so about 6 months ago I swapped out the thermostat, not BMW part tho, the one I removed wasn't either.
All appeared OK till a recent spirited drive, temp was normal but only the top hose and the top passenger side of the radiator was hot, bottom hose was cold and that side of the radiator was cold too. I have a fan switch which did work but as that side of the rad is cold it won't kick in. A lot of pressure build up too. Car runs fine though. bled the system and put new antifreeze in.
I have removed the stat, put 12volt on the connection and it open the stat, the water pump is OK too. Refitted stat and ran the engine, I clipped into the stat wiring to check for signal, there is some pulsing voltage so happy that electrically I'm fine but I would like to know what to expect here. Out for a run a couple of miles, still the same top hose hot bottom hose cold. I put 12 volt to the stat when engine running and seconds later hot water flowing through rad via both hoses. So question folks, is this stat temp and ecu controlled.If so could the stat be bad and I should have gone for oem?
Hoping it's not head gasket. Any thoughts. Mine are to go for oem stat as the easiest lowest cost option.
And of course my first sprint event is in 2 1/2 weeks
Cheers and happy Zedding

 

[the Nefyn cat]

Top hose should be hot, bottom hose should be cold, all to do with hot water coming out of the engine and cooling as it passes down through the radiator/ Thermostat opens according to how hot the coolant is, no electrics involved.

 

[Mint]

...
Thermostat opens according to how hot the coolant is, no electrics involved...

mmmm not sure about that. Certainly true on the early models, but my 2002, M54 engined 2.2 does have an ECU controlled thermostat.

 

[t-tony]

How does that work? My E85 had no electrical connections to the actual thermostat itself.

Tony.

 

[Mint]

How does that work? My E85 had no electrical connections to the actual thermostat itself.

On mine there's a two pin plug on the thermostat body. The ECU takes an input from the coolant temperature sensor on the front of the engine. The thermostat is a 'Map Controlled Heated Thermostat', it has an element inside which is controlled by the ECU.
Seems over complicated to me...

 

[MartinN]

Hi, yeah same as Mint, ill be looking again today once this rain stops. Thanks for the input folks.
This onlyshowed up after I had the injector rail off to clean the unjectors, my thought is i have disturbed a temp sensor, or not plugged it back in.