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Repair Questions and Answers.

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 #377211  by hamnmerdown
 January 4th, 2019, 12:46 pm
Hi all, I recently purchased a 2000 300m (197,000 mi) as temporary car while I searched for a Software Development position. So far I've really enjoyed the vehicle but I've had some issues with the cooling system.

Right after I bought it, the car overheated because the heater hose detached from below the intake manifold which I had to have fixed. My mechanic didn't trust an aftermarket hose so he just bolted the old one back on.

Everything was fine until a couple of months ago when the coolant boiled on one occasion. Then it was again fine until recently driving in a heavy rainstorm it boiled over and I noticed the radiator cap had loosened and had cracks in its upper gasket. I replaced it with a 17lb mopar cap.

Then after the second drive with the new cap, when I parked I got steam from under the bonnet, lost coolant and got the same 'hissing sound' from under the manifold. Even with these recent issues I have not seen the temp needle crack halfway.

I took it into my mechanic to look at and he could not find anything wrong with it other than it needed to be bled of air properly and more coolant added. I've driven it 3 times since and on the 2nd time I noticed coolant beneath the car.

The main question I have is where does the coolant go if the recovery tank is overfilled? I'm thinking he simply overfilled it as the recovery tank as it is really cloudy and yellowed. The hose on the bottom of the tank leads behind the engine where coolant appears to be leaking from. Is that where the system would dispose extra coolant? The service manual says nothing about where extra coolant goes.

Also there is a tiny little space on the front of the engine where I can see under the intake manifold and confirm the heater hose is still attached.

Greatly appreciate all who read this long post.
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 #377213  by Sneke_Eyez
 January 4th, 2019, 1:13 pm
First - welcome to the forums!

I bet your overflow tank is cracked. It is easy to miss a crack, they often crack at the bottom where it is tough to see and then cause pressure issues.
Due to where the overflow hose location is (left hand side of the tank), it is possible that it even looks like it is just coming from the overflow.

I'd check that tank out very well and replace it.
They make aftermarket tanks, but they have been shown not to last - so it is an item where we recommend OEM only replacement.
 #377214  by cin993
 January 4th, 2019, 1:20 pm
Since you've seen a coolant leak on the ground then you obviously have a leak. Few years back i also had a small leak that i fixed with some great advice from this forum

You can rent for free a coolant pressure tester at an auto parts store. It is easy, tester attaches where the radiator cap goes.

With the engine (and coolant) cold, pump up the tester to 17psi and look for leaks. could be leaking from the thermostat housing, rad hose, radiator itself, water pump, loose hose clamp, cracked plastic coolant tank, etc
zerex g05 coolant is recirculated, not disposed. probably just a leak. good luck
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 #377221  by hamnmerdown
 January 4th, 2019, 11:43 pm
Thanks for your input. I don't think it is a cracked radiator or water pump as the coolant is dripping from the rear of the engine. The ground underneath those components is dry.

I will try to look harder but I don't see any obvious leaks coming from the recovery tank.

The coolant is dripping onto what I think is the stabilizer bar. It also appears to be more towards the drivers side than the passengers side. The back driver's side corner of the engine appears to be wet although that could be oil from the valve cover.

Any chance it is an external head gasket leak? I know those are supposed to be rare on these vehicles. I have been checking the oil a lot as my mechanic just deleted the oil cooler to fix the a oil cooler line leak. Haven't noticed any contamination.
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 #377224  by FIREM
 January 5th, 2019, 7:14 am
Head gaskets rarely if ever fail on the 3.5. Many other leak points must be checked first.
Pressure test cold and look for the actual exact source of the leak.
Hoses, overflow tank,radiator tanks, thermostat housing, heater pipe near starter, heater pipe and or oring under LIM, LIM gaskets, bleader valve, water pump, block to front housing seals, all suspects.
Note: LIM and heater pipe may fill the valley then drip out weep hole rear of block.
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 #377320  by hamnmerdown
 January 11th, 2019, 12:30 am
Update. It was the LIM hose that was leaking again. My mechanic said it was leaking through the o-ring. He didn't charge me for the repair considering his original repair from September failed within the warranty period.

I asked him if he used a generic/wrong o-ring on the original repair but he said he used the official part. Any ideas on why the LIM failed again after only 4 months? Maybe due to the two coolant boil-overs I had?

This is the first time my 300m hasn't leaked anything since I bought it 5 months ago, which is nice.
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 #377322  by In-trepid
 January 11th, 2019, 3:26 pm
Hard to say what caused the issue and what was a result of the bad o-ring. This is not a normal o-ring. It is square cut versus the typical rolled o-ring. I've never heard of one failing that quickly.