[cpat414]

Hi all, long time/first time

Been reading through the threads and I thought I figured this out but still having some troubles.

Recently replaced thermostat after car wouldn't keep @ temp, monitoring from OBC highest I would get was around 86 degrees C (it's been cold here in Seattle).

Also got P0128 code.

After replacement of thermostat (Mahle TM1397) and expansion tank (due to large crack) I think I think I've got everything buttoned up, no leaking, but when I drive the car the temp still drops into the 70s. No fault code... yet.

So here's what I think could be wrong, let me know if I'm missing something obvious:

1. Thermostat I bought is bad, go get OEM part
2. Replace temp sensor @ cylinder head
3. There's still air in the system and I need to bleed it more?

I don't know what else, any thoughts? Water pump?

Vehicle is 2003 330CI manual trans

 

[Bali]

There have been many cases of new Mahle/Behr thermostats opening too low, so this is a good possibility.
Test your old one and this new one in hot water with an IR thermometer to see when they open.

 

[Sapote]

Thermostat I bought is bad, go get OEM part

* Do a long drive and then stop car and while idling, reach down and feel the lower hose in your hand; warm, cold, hot?

* I somehow think the issue is not the Tstat. put old and new ones in water pan and cook them. Watch carefully to see when it start open and notice the water temperature. If they opened way before boiling (70 or 80C) then they are no good. They should start open just before boiling, around 97C.

* How did you bleed the thing, in detail steps?

 

[AsdAsd]

Mahle thermostats are junk. Mine was opening too fast from new aswell. Got a second new Mahle installed, works fine, but when I floor the car, the temps drop too low to ~70C. A friend had the same issue. Borg warner thermostats work fine...

 

[Bali]

when I floor the car, the temps drop too low to ~70C. A friend had the same issue.

It is supposed to do that, as commanded by DME under high temperature or load.

 

[AsdAsd]

It is supposed to do that, as commanded by DME under high temperature or load.

Yes, it is commanded to drop to 82C, mine goes lower than 75 so the gauge starts moving down.

 

[Bali]

Yes, it is commanded to drop to 82C, mine goes lower than 75 so the gauge starts moving down.

Ok, then that may be a problem. I do not recall the target coolant temperature when DME commands map thermostat to open wider.

 

[elfer]

That DME command works by electrically heating the wax of the thermostat to make it open on WOT when the water temp alone isn't sufficient to. If you unplug the electrical connector from the thermostat there'll be no power to the heater and you'll remove DME map control from the equation. Do that and go for a drive. If the coolant still sits at 70C like before then it wasn't the map heater. If now it goes up to 97C then it was.

 

[cpat414]

Yes, it is commanded to drop to 82C, mine goes lower than 75 so the gauge starts moving down.

yep same here, the gage goes below 12:00

 

[cpat414]

* Do a long drive and then stop car and while idling, reach down and feel the lower hose in your hand; warm, cold, hot?

* I somehow think the issue is not the Tstat. put old and new ones in water pan and cook them. Watch carefully to see when it start open and notice the water temperature. If they opened way before boiling (70 or 80C) then they are no good. They should start open just before boiling, around 97C.

* How did you bleed the thing, in detail steps?

I'll give this a try.

To bleed:
slowly add coolant into ET with bleeder screw out. Add coolant until coolant coming from bleed screw is solid (no bubbles) with heater on high temp, low fan. Suctioned out excess from ET to get between min and max. Drove the car a couple miles, let cool down and checked level, had to add a tiny bit, less than a cup.

I also noticed I was overheating so now I'm thinking WP. Based on this description from Pelican, I'm going to go see if I can feel the line pressure:

"When you accelerate, the engine temperature will drop. Now, this is not always indicative of a faulty water pump, but it's a good starting point. You may also want to try squeezing the top radiator hose with the engine warmed up and running if you suspect your E46 water pump to be failing. You should feel pressure build up on the back of the hose and surge once you release pressure off the hose. If you feel no pressure, it's a fair bet that the water pump is failing and it needs to be changed as soon as possible."

BMW E46 Water Pump Replacement | BMW 325i (2001-2005), BMW 325Xi (2001-2005), BMW 325Ci (2001-2006), BMW 325ti (2001-2004) | Pelican Parts Technical Article

 

[Sapote]

slowly add coolant into ET with bleeder screw out. Add coolant until coolant coming from bleed screw is solid (no bubbles) with heater on high temp, low fan. Suctioned out excess from ET to get between min and max. Drove the car a couple miles, let cool down and checked level, had to add a tiny bit, less than a cup.

I don't see at which point the bleeder is closed -- before or after the excess coolant was removed?

 

[cpat414]

I don't see at which point the bleeder is closed -- before or after the excess coolant was removed?

I believe I closed the bleeder screw before removing excess coolant

 

[cpat414]

I'll give this a try.

To bleed:
slowly add coolant into ET with bleeder screw out. Add coolant until coolant coming from bleed screw is solid (no bubbles) with heater on high temp, low fan. Suctioned out excess from ET to get between min and max. Drove the car a couple miles, let cool down and checked level, had to add a tiny bit, less than a cup.

I also noticed I was overheating so now I'm thinking WP. Based on this description from Pelican, I'm going to go see if I can feel the line pressure:

"When you accelerate, the engine temperature will drop. Now, this is not always indicative of a faulty water pump, but it's a good starting point. You may also want to try squeezing the top radiator hose with the engine warmed up and running if you suspect your E46 water pump to be failing. You should feel pressure build up on the back of the hose and surge once you release pressure off the hose. If you feel no pressure, it's a fair bet that the water pump is failing and it needs to be changed as soon as possible."

BMW E46 Water Pump Replacement | BMW 325i (2001-2005), BMW 325Xi (2001-2005), BMW 325Ci (2001-2006), BMW 325ti (2001-2004) | Pelican Parts Technical Article

* Do a long drive and then stop car and while idling, reach down and feel the lower hose in your hand; warm, cold, hot?

* I somehow think the issue is not the Tstat. put old and new ones in water pan and cook them. Watch carefully to see when it start open and notice the water temperature. If they opened way before boiling (70 or 80C) then they are no good. They should start open just before boiling, around 97C.

* How did you bleed the thing, in detail steps?

Just boiled the old thermostat, it worked just like it's supposed to Opened just before boiling

 

[Sapote]

Just boiled the old thermostat, it worked just like it's supposed to Opened just before boiling

Maybe the Tstat electrical heater is turned on all the time and causing the Tstat to open too early. Test drive again with the Tstat 2-wire connector removed.

Recently replaced thermostat after car wouldn't keep @ temp, monitoring from OBC highest I would get was around 86 degrees C (it's been cold here in Seattle).

I also noticed I was overheating so now I'm thinking WP.

I'm a little confused here. Display shown coolant temp was 86C (not hot enough) and engine was overheated?

So with the Tstat confirmed working properly in boiling water and having reported 86C coolant and overheat issue, I think you might want to try with the Sapote bleeding method:

Sapote method, rev1:
1) engine cold, car head up on slope driveway or flat ground level is fine.
2) remove bleeder and tank cap, fill coolant to the MAX marker on the tank using the red rod as indicator. Do not overfill to top of tank.
3) close the bleeder, set heater to hot and fan low, run engine at idle. Don’t turn off engine until the end. Important: Do not let engine running more than 7 minutes total while the tank cap is not closed, to avoid damaging the cylinder head.
4) Crack open the bleeder to let air out and close it when no more air bubbles. Top off the tank to MAX marker. Close the bleeder and screw the tank cap by one turn to avoid coolant shooting in next step when rev-ing up the engine.
5) Rev it up to about 2500 RPM a few times to push out any air pockets (in the head and the heater core) into the upper hose/tank. Keep engine idling for next steps.
6) Crack open the bleeder again to let air out and close it when no more air bubbles. Top off the tank to MAX marker. Close the tank cap.
7) Test drive and check for having heated air in cabin. Done.

 

[AsdAsd]

Just boiled the old thermostat, it worked just like it's supposed to Opened just before boiling

I would first get a genuine, or borgwarner thermostat. Another friend of mine bought 3 new mahle units, all of them were faulty. Swapped it out with a borgwarner unit, all works as expected. I suspect the electrical heater in the mahle thermostats does not work as intended

 

[Sapote]

I would first get a genuine, or borgwarner thermostat. Another friend of mine bought 3 new mahle units, all of them were faulty. Swapped it out with a borgwarner unit, all works as expected. I suspect the electrical heater in the mahle thermostats does not work as intended

But OP also have engine overheat issue, so the Tstat heater part cannot be blamed for this. How could one has 86C running too cool while also has engine overheat issue? So must be air pocket in the system.

 

[MrMCar]

I'm stretching hard to offer an answer. However usually when air pocket, there's steam in the head and temperatures skyrocket very fast...

 

[cpat414]

Hi all sorry for the confusion. Temp went over a 100 while test driving while I had the radiator fan out. I am assuming this is the reason. Been driving last day or two with fan back in and no overheating.

Still struggling to get to temp while moving. While stop and go or idiling I’m right at 12:00.

Will try removing the thermostat heater cable next time it’s cold.

 

[AsdAsd]

Does not need to be cold, just remove it and go into the hidden menu on the cluster: BMW E46 - How to display coolant temperature digitally through the cars OBC - YouTube
If the car stays at 97C, the thermostat is good but the heating element is bad or the DME sends the wrong signal.

 

[elfer]

Hi all sorry for the confusion. Temp went over a 100 while test driving while I had the radiator fan out. I am assuming this is the reason. Been driving last day or two with fan back in and no overheating.

Still struggling to get to temp while moving. While stop and go or idiling I’m right at 12:00.

This made me wonder. Have you ruled out the fan being on (or on full speed) all the time? On the manual cars it should only come on when needed, commanded by the DME. If you have INPA there's a test you can do where you tell it to spin at 0%, 25%, 50%, 75% or 100%. If you step through those with the engine off you'll be able to hear when it's on (or you can get out and check) and the pitch will increase with speed. Or you could just start the car with the engine cold* and make sure it isn't spinning.

*question to fellow fanatics: would the AC need to be off too?