Non MB but engine running cool

[Charles Morgan]

My 3.5 litre straight six in my BMW M535i is running cold and barely getting out of the blue zone on the temperature gauge, it is also gulping petrol. No heating either

I have changed the thermostat (no change) and because it was previously overheating at idle, the viscous fan coupling, which had gone, now no problem from that.

What else would the collective here think might be at issue? It's had a new rad and a top end overhaul in the last 3 years, so I'm a little stumped.

 

[gbjeppm]

Is it an E39 Charles?

Assuming yes, symptoms still sound like thermostat stuck open, and it would not be the first time a new thermostat does not work.

Alternatively there may be air in the system, so needs to be bled and topped up through the bleed screw near the thermostat with ignition on and pump rUnning. Preferably with the nose in the air. Loads of how to guides on the interweb about doing this.

Running cool would also explain the fuel usage.

 

[Charles Morgan]

E28.

I'll give a bleeding a go before looking at the thermostat.

 

[Red C220]

No heating would lead me to look at a blocked matrix maybe?

I'm not sure how that would relate to running cold though and increased fuel use.

How does the cold start system run on this engine? If it's getting a signal that the engine is cold it could be overfueling.

 

[Charles Morgan]

I changed the monovalve on the heating system (previously running inside the car in summer), so it's probably installer error on the heating, never actually opening.

It's Bosch Motronic, so it will be very rich on cold start. It might be the coolant temperature sensor.

 

[John Jones Jr]

Excessive amount of undiluted coolant in the system, ie incorrect coolant/water mix?

 

[carat 3.6]

Sounds like air in the system Charles. If after bleeding it the heater still wont work, the duo valve is probably stuck or dead.

They normally like to run at around 85 - 90.

 

[Red C220]

Sensors are where I'd start first, at least they are generally cheap.

If the temp sensor is misreading that would explain high fuel use as it would run the cold start injector for longer than required. The lack of heating might be coincidence due to the potential valve issue.

 

[John Jones Jr]

Sounds like air in the system Charles. If after bleeding it the heater still wont work, the duo valve is probably stuck or dead.

They normally like to run at around 85 - 90.

+1.

I had a problem bleeding my old E32 735i also with an M30. Ended up having to raise the front on ramps, back filling the rad hoses and filling the block first with coolant then fitting the thermostat.

 

[carat 3.6]

+1.

I had a problem bleeding my old E32 735i also with an M30. Ended up having to raise the front on ramps, back filling the rad hoses and filling the block first with coolant then fitting the thermostat.

Sounds familiar Jhon, the heater was always a bitch to bleed on my e34. The e30 has never had any such problems yet though.

 

[John Jones Jr]

Sounds familiar Jhon, the heater was always a bitch to bleed on my e34. The e30 has never had any such problems yet though.

Simon, don't talk about E34's especially with M50's. I had to get a BMW tech to bleed that as I was afraid I was going to blow the H/G or worse!

P.s. if I recall correctly the first thing to do there is to loosen the heater hoses at matrix.

 

[carat 3.6]

Simon, don't talk about E34's especially with M50's. I had to get a BMW tech to bleed that as I was afraid I was going to blow the H/G or worse!

P.s. if I recall correctly the first thing to do there is to loosen the heater hoses at matrix.

Yep, those are almost as bad as the k series twin cam for warping heads and moving liners.

I pull the hose off completely once it's up to temp, hold the rev's up till she shoot's a continuous stream of coolant from the heater, then shove the hose back on while it's gushing out. Work's like a charm.

 

[StuartK]

Reminds me of the days I used to place cardboard over the inside of my grille

 

[Ted]

Another vote for faulty thermostat, or possibly in some way incorrectly fitted.

 

[camerafodder]

Another vote for faulty thermostat, or possibly in some way incorrectly fitted.

+2 from me too.

 

[Bellow]

Check stat by firing up engine from cold and immediately taking hold of stat output hose.
If hose remains cool then at some point (minutes) later suddenly gets hot then stat is fine.
If hose immediately shows signs of temp (albeit low) then stat is stuck open.

 

[brucemillar]

Charles From my tortuous experience with this problem my Pajero. Do check the gauge is reading correctly!! Drop gauge sender into kettle of boiling water. Check gauge reads 100. I have an infra red laser thermometer you can borrow which I bought to verify my diagnosis. It immediately shows hot/cold spots. Let me know.


Sent from my iPhone using MBClub UK

 

[brucemillar]

Charles

I can post the thermometer to you. Or you can pop over here. I have a fully stocked tool kit and ready supply of Bakewells.

The great thing about the infrared, is it is showing you in real time what temps your engine is really running at.

I had replaced almost my entire cooling system chasing a "fault". Two minutes with this beastie and the problem was staring me in the face. I could read the temps in every bit of the system without getting my hands dirty. I saw poor flow in the rad (cools spots) but good temps at the thermostat housing and top & bottom hoses. The kettle test then showed that my gauge had an over-read of 17 degrees. Where I believed that my engine was running hot at 97 on the gauge? it was in fact perfect at 80.

My problem was caused by a blocked rad core. All the standard visual checks looked good. I could see coolant flow left to right, top hose was hot, bottom hose cooler etc. Warning: I also had to try two thermostats. The brand Blue Print one did not open at 82. A genuine Mitsubishi one (twice the price) opened bang on 82.

 

[coupe addict]

Failed or inadequate gasket on the thermostat will have the same effect as thermostat stuck open.
Steve

 

[brucemillar]

Failed or inadequate gasket on the thermostat will have the same effect as thermostat stuck open. Steve

Steve

Is this due to air getting sucked into a sealed system?

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