Thermostat Question

[championc]

I have a 316i 1.9 M43 and the thermostat is the L shaped type that connects into the front of the engine. There is an electrical connection onto the elbow of the thermostat housing. I disconnected it but th temperature needle still stayed at 12 o'clock so this obviously doesn't have anything to so with this.

Would this be the connection that detects when the car has heated up sufficently enough to then send a message to the ICU to then reduce the mixture (acting like an electronic choke) ?


Cormac

[Philly]

I would presume it has something to do with sending the engine temp to the computer to let it know when to/not to kick the fan on, thats my best guess. A long with what you said seems to make sense too.

The thermostat in good working order in conjunction with a good working engine will not allow it to get passed the 'middle' of the temp gauge. Thats why you hear all these things about the thermostat failing 'open', allowing it to get hot.... or 'closed', not allowing it to get hot

[championc]

Thanks rwd_king

The reason for my question is because my car runs for about a half an hour before the mixture seems to lean out. I can tell from the OBC that the MPG is low until about a half hour through my drive to work and then suddenly the MPG will start to rise dramatically.

My problem is that the temp needle will have reached the middle point after about 10 minutes of driving so it's a further 20 minutes or so before something kicks the ICU.

If I used a continuity meter across this connection, should it be Open, Closed or would anyone know the ohn readings during cold and hot ?


C

[roadrash]

Originally Posted by rwd_king

thermostat failing 'open', allowing it to get hot.... or 'closed', not allowing it to get hot

Are you sure that's correct? I thought that if the thermostat failed open, it would allow coolant to continually circulate, therefore allowing the engine to run cool. Conversely, if it failed closed, the coolant would not circulate therefore allowing the engine to run hot. I could easily be wrong about that though.

[championc]

Either way, hopefully you know what I mean. I somehow need to confirm if I have a lazy thermostat or lazy sensor or whether my problem and solution exists elsewhere


C

[roadrash]

Back to the original question...

Perhaps if you found that part at realoem.com, the name of it might give a clue as to what it's actually for?

[mohaughn]

It should not take 10 minutes for your car to warm up...

Based on how long it takes for your car to warm up I would say the thermostat is shot. The thermostat is mechanical. You can't test it with an electrical test gauge. The only test would be to pull it out and see if it stays closed when cold, and opens up when hot.. But if you are going to pull it out, just replace it. They are cheap.

[Philly]

roadrash, your probably right... Im still picking up little packets of information as I hear it, alot on the fly and I probably get alot of information crossed in my head.


Either way Champ, just replace the thermostat, its not very expensive nor is it a hard job to do... and its good maintenence anyways... Im 90% sure that will fix your problem based on what your saying.

I had a bad thermostat for a little while, it just stayed just below half all the time, which did not bother me enough to buy a new one. Conversely though, I don't know if 'underheating' could hurt anything...

[championc]

As a final test on my my home from work this evening, I drove off and once the temperature needle was exiting the blue mark (about 10 o'clock), I stopped the car and popped the bonnet and checked the pipe exiting the thermostat.

Surprise surprise, it was warm which was confirming that the thermostat was allowing the coolant to circulate around the radiator circuit. However, to completely confirm this, the exit hose was ALSO warm. This confirms that the thermostat is stuck closed (have I got the open and closed the right way around).

I'm sorry I didn't do this simple test ages ago but I had presumed that the temperature needle was fed from the connector on the thermostat which was obviously wrong and I can't wait to see the difference in my MPG figure. It's generally about 17MPG when the choke is on and 30+ when off.


C

[mohaughn]

In your original question you asked if the temp sensor that controls the needle is the same as the ECU temp sensor. It is not. Atleast on a US 318ti it is not.

My car has two temp sensors. One is called the coolant temp sensor, and the other is called the engine temp sensor. One for gauge in the car, one for the ECU.

[championc]

Hi mohaughn

Thanks for that. I really only discovered this after disconnecting the wiring connector and then discovering that the needle never moved. At least I know that there is nothing wrong with the engine temp sensor and it would appear that the coolant temp sensor and it would appear that this is the one on the elbow of the thermostat and that also feeds the ECU.

I have to say that I would never have discovered the problem had it not been for the installation of the OBC which I only did as a "nice to have" option after getting the bits cheap on eBay.

When I zero'd the MPG before setting off, it hovered at the sub 20 mark until a half hour into my journey when it then would suddenly rapidly increase. Sometimes this wouldn't happen and this would obviously occur when the air would cool the coolant around the coolant sensor too much thus "tricking" the ECU into thinking that the engine was cold.

I should ask everyone out there to confirm, I assume that the coolant pipes to and from the radiator should be completely cold until the thermostat shuts after the engine has reached it's running temperature ?


C

[aceyx]

One will be warm, the other will be hot. Throwing a cool liquid at hot metal is a bad idea all around.