[Soul_Glo]

Not another engine oil temperature thread!

My engine oil temperature gauge has started wobbling/fluctuating at idle and when driving. See idle video here:

This is on our 325i SE Auto - E92 N52K 218PS

What a pain! Only replaced the oil level sensor a few weeks ago.

Anyhow... this happens when stationary, when driving around town and on the motorway the fluctuation is slightly smaller with about a 2 degree C swing under and then back to 100 C.

I accessed the BC hidden menus for coolant temperature while driving and those seem to be in check. So the water pump and coolant are doing their jobs.

I am thinking it is either a faulty oil condition sensor or faulty gauge. Any help would be appreciated.

Muchas Gracias Muchachos

[Soul_Glo]

Update 27/03/15. My indy thought the oil condition sensor was at fault. We replaced it second time and even swapped it out with one from another car but no joy. The ground and wiring is all sound. I don't know why but I suspect the oil pump. Stumped!

It went into the dealership and the dealer has said that the ECU is at fault. That is one hell of an expensive part and very unusual for it to have failed. We (indepdent and I) think that the dealer is taking a stab in the dark here. It is going to be claimed under warranty.

[Soul_Glo]

Update 03/04/15: a technical line has now been opened to Germany. The problem is still there. I guess they thought it was electrical and threw parts at it. There is a metallic tinkering and sometimes clatter from 2000-4000 rpm when accelerating between 40-50mph. It sounds like it is coming from the engine. I remembered this and told them. Let's see what happens.

[ellinara]

Hi Broken Gearbox,

Sorry to hear about your problem. My gut is telling me that it is the thermostat. My reasoning is that if the thermostat is not open fully then there may be just enough coolant passing to allow for the engine to cool however it is not enough to keep it cool. The reason why you see the oil temperature fluctuate could be the cold air that flows into your engine bay and onto the rad thereby further cooling the coolant. In doing so, the colder coolant will travel to the engine and cool it further however, the temperature will increase again at idle due to less air flow.

Not sure if it makes any sense. Im just hoping that its the thermostat because it will be way cheaper than a new ECU or water pump.

Hope this helps!!!

[Soul_Glo]

Interesting theory. I think it is worth looking into when I get the car back. There are some knowledgable technicians out there and then there are some who follow the computer. If the computer says go left they go left even if their instinct may say different. Problems like this need an old school approach of tracing wires to their origin - wires fray, wires over heat and ground points do go bad. They have replaced the oil pump but there is no way there could be that amount of cool oil in car to make oil temperature swing up and down by 5-10C when driving. I am now suspecting water pump / cooling system. A friend had an E39 and someone had tampered with the wiring in it's life... So the gearbox temp sender and thermostat were on the same ground. The ground went bad and the gearbox had problems! They said they have checked the grounds but how thorough? Who knows. The saga continues...

[Soul_Glo]

Update 14/04/15. The DME was dying. It was sending false signals to various other sensors and causing poor running.

I investigated everything I could such as idle control, vanos, breathers, vacuum, crank shaft position, engine speed sensors, grounds etc.

Symptoms were the following as it became worse and worse:
- Engine bogging on power
- Oil temperature swings on gauge (as above)
- Decreased fuel economy
- Intermittent loss in power. When driving it would switch off/shut down for a split second and fire back into life instantly. At first I thought this was DSC related but it was not.
- Power delivery was not as linear
- Automatic transmission rough shifts
- Oil temp varied. I never saw anything above 100C when driving most days. Even on an urban run I never saw 110C

The dealership pulled a long code. I do not have it to hand but if I remember to upload it then I will.

There was no water damage to the DME. However, some components inside had over-heated somehow the dealer says. They also assured me that it is not a common fault?!

The car feels like brand new. I mean this thing goes... and it is like it has just been picked up out of a showroom. All the linear power is there and it is hitting all the right temperatures in the right conditions as it is supposed to according to its maps. I never noticed this fully because when I brought it I thought it was just a crappy under powered 325i but it pulls much better and stronger and I am in love with the darn thing.

Result!!!