Hello. I have a 2003 300M with 120xxx miles. 2 months ago I changed the thermostat which led to having to replace the heater return tube (rotted where it turns to run up the block). After sitting for two months, I finally saved up enough and bought the return tube (under the exhaust manifold) and after a few choice words and a pack of smokes got it installed. *The car sat without any coolant this entire time* I bled the system the best I could and started home. After driving for maybe 15 minutes the car began to overheat. I pulled over and upon opening the hood there is a small puddle of coolant on the intake manifold just below the injectors. I thought that may be from bleeding the system (no tubing available) and that maybe i didnt bleed the system correctly. After the car cooled down i started it a few times but it stalled immediately. I let it cool completely at this point. Started it and drove about 5 minutes with the same results and scenario. Coolant seems to puddle on the intake manifold and on the ground below the passenger side of the motor. Any ideas as to where i should start with this one??? It has a new thermostat, coolant tank and heater return tube. Please Help!

 

do a pressure check of the cooling system see where it is leaking from

 

Maybe I should have thought of that? I will rent the tester and see. Thank You for the advice. I will post my findings here.

 

I did a pressure check on the system. It has a slow leak down. Another member mentioned the "O" ring under the intake. Bought the O ring and upper/lower intake gaskets. Cant seem to get the intake to come off. Going to look at it again tomorrow, maybe pull the throttle cables and ???? Any one have advice on removing the intake?

 

that o ring in question is not on a 3.5 motor it would be on a 2.7
Keep looking for the leak

 

Im glad I saw your post before I got too far... just spent 50.00 in gaskets glad i didnt waste them yet!

 

There is an o ring on the coolant tube on a 2003 3.5 under the intake. To get the intake off there is a hidden bolt under the throttle body that goes to a bracket that attaches to the trans to block bolt. The bolt is a 10mm, you will have to pull the fuel rail to get the intake off.

 

So I ended up cutting my loses. I took the car to a local shop and I am waiting to see what they say. The car is not leaking coolant now but instead takes its time to slowly overheat. I am certain that the low speed fan relay is bad, but other than that, I think it was time to let a pro take a look. I am usually not one to accept defeat, especially when it comes to vehicle repair. But this car is unlike anything I have ever worked on. I will post the mechanics findings here for everyone's knowledge.

 

doubt a fan relay would do it because it is only on when the car is sitting still at a stop light now used while driving down the road. More then likely warped heads.

 

You are correct. The shop said the heads are warped or the head gaskets are bad. I am not trying to do a head job in my driveway so I am going to try some Blue Devil Head Gasket Sealer and see what that does. They quoted me $2,000.00 to do the heads, and the car isnt worth much more than that. I will post my Blue Devil finding once I have given it a try.