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2003 330CI MT
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Discussion Starter · #1 · (Edited)
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
 

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2003 330CI MT
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Discussion Starter · #10 ·
* 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
 

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2003 330CI MT
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Discussion Starter · #13 ·
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 :confused: Opened just before boiling
 

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2003 330CI MT
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Discussion Starter · #18 ·
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.
 

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2003 330CI MT
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Discussion Starter · #26 ·
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.
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.
Have been driving last two days with the tstat plugged in and unplugged, no discernable difference. Temp never gets up to 97, and only into 90s when idling/stop and go

I guess I'll be trying a new tstat
 
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