Big problems with my new toy today. I have a few questions and need some advice from the experts, so anything you can offer would be very helpful.

2006 E320CDI with 150K miles

Driving home from work today, the car went into limp mode (no power steering, ac, etc.) and red battery symbol came up with the "visit workshop" warning.

I limped it home keeping a close eye on the temperature gauge, which never moved up.

I opened up the hood and found the serpentine belt coiled up at the bottom front of the engine. Taking a closer look, I could see that the pulley on the water pump was marred up and trying to spin it found it to be stuck.

So that pretty much tells me that the pump seized and threw off the belt, so I'm about to order up the pump and belt and get ready to do the R&R this weekend.

Three questions, please:

1. Because the engine temp never went up when the coolant pump wasn't running, is it possible that there are backup electrical pumps that ran in limp mode? What else could explain the temp not increasing? Bad temp sensor?

2. In various places around the front of the engine, there is dried, cream-colored spatter that seems to be centered around the water pump (not sure because I don't have the front apart yet; Having trouble getting the site to load pictures from my phone, but I'll keep working on it)

3. What else should I plan on replacing while I have the front apart? I don't have much in the way of service history on this car prior to 148k when I bought it.

Any advice at all would be appreciated.

Thanks,
Pete

 

Replace at least the coolant with MB brand, the thermostat and, since the belt is off, spin all the pulleys. If any make a noise replace them. Use genuine MB parts only. I'd do an oil change and replace hoses and clamps. Consult a good indie about the muddy coolant since it was possibly never replaced for possible head gasket issues.

Sorry bud and good luck.

 

Keep us updated too.

150k sounds like these parts were past due about 30k ago, following the common sense laws.

I'm at 100k right now, and I know I need to replace the hoses, water / thermos, pullies.. :-/

 

Last night I did the following:
Removed front radiator cover
Removed fan/shroud assembly
Drained radiator
Removed water pump
Removed tensioner pulley

Here's what I found; The bearings on the pump are definitely shot. But what was troubling was the belt tensioner pulley was SMOKED. It was all torn up and it was obvious that some of it had melted - but the bearing was still good. Strange.

I'm having trouble theorizing what might have happened after the pump bearing failed. If the bearing on the tensioner pulley had frozen then I could easily explain why it was all torn up, but the bearing was good and besides the chances of the bearings on both the pump and the pulley going bad at the exact same time are so high as to make it impossible.

The belt itself if quite a tangled mess - i.e. it is all coiled and can't be made "flat" anymore. That tells me that it might have been severely stretched - unevenly (more on that in a minute).

Looking closer at the tensioner pulley, in the areas that aren't melted or torn up, I can clearly see areas on the surface where it had become indented at less than the width of the (natural) belt. I'm theorizing here: This tells me that the belt somehow became under extreme tension, stretched and narrowed and pushed into the surface of the pulley possibly locking up the pulley bearing enough that it wouldn't spin. All of this happening very quickly, mind you, the belt, becoming tighter and tighter because of the locked up water pump bearing and pulley bearing finally slipped on the pulley surface under extreme tension causing very high friction and melting/tearing up the pulley before it finally slipped off the circuit altogether. - yikes.

I now think that the white (cream colored actually) spatter was melted nylon from the pulley getting toasted. Kinda weird. (see attached images of the spatter)

Anyhow, the pump, gasket and belt are arriving from thebenzbin.com on Friday, I will pick up the pulley and coolant from the dealer before then and put it all back together on Saturday.

 

Oh, and like I said in the opening, I drove about 2 miles on side streets without the water pump running. The temp gauge never went up, but the engine seemed awfully hot.

Is anybody out there that think I should be concerned about an overheated engine?

Thanks to all.

 

Compression test is the only way to know for sure.

I think you got very lucky in catching this though. Yikes.. I better replace my pullies and stuff soon...