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Came across this article from a Mercedes Tech describing a common issue in our GLK 250 OM651 Engine. I have had to "top up" my coolant a couple times in the last 3 years and this has me worried I have this issue. Anyone else have any ideas or info regarding this issue or how to check or test for it? Thanks. Quote and link provided below.
Quote:“ Water Pump OM651 four cylinder BlueTec (Service Bulletin LI07.09-N-063338): The OM651 water pump is different from any other Mercedes water pump, and not in a good way. It uses a vacuum valve inside the water pump. Sooner or later the vacuum element leaks. When it does, antifreeze is sucked into the vacuum system. You’ll typically notice the “Low Coolant” warning light comes on with no obvious leak. Doo not ignore the leak and keep adding more coolant. If you ignore the leak you’ll quickly see the CEL. Now you’re in trouble. Coolant will migrate into the Brake Booster and Vacuum Pump. From there it will move into the electrical system and contaminate the engine computer. Coolant will finally get into the engine oil and ruin the engine. It can cause thousands of dollars in damage.”
Yep, I've received that letter earlier this year. Took the Bluetec in to get that software update.
I should also mention I just recently had the OE water pump replaced with the updated metal impeller version, along with new belt, tensioner, idler rollers and coolant.
I think the shop didn't top off the new coolant sufficiently because I could hear some gurgling in the heater core in the dash when it begins to warm up, and also because I got a "Low coolant" warning notice in the cluster the other day.
So I will be topping off with distilled water and then keeping an eye on the level in the expansion tank.
Edit: if coolant leaks out of the new pump and ever finds its way into the engine thus ruining it, I'm assuming (or rather hoping) the AEM extended warranty covers that. It covers a ton of stuff unrelated to emissions anyway.
Last edited by andreigbs; May 2, 2023 at 03:49 PM.
Yep, I've received that letter earlier this year. Took the Bluetec in to get that software update.
I should also mention I just recently had the OE water pump replaced with the updated metal impeller version, along with new belt, tensioner, idler rollers and coolant.
I think the shop didn't top off the new coolant sufficiently because I could hear some gurgling in the heater core in the dash when it begins to warm up, and also because I got a "Low coolant" warning notice in the cluster the other day.
So I will be topping off with distilled water and then keeping an eye on the level in the expansion tank.
Im on original water pump working OK as of now but am worried about this leaking coolant into the vacuum line issue. You have a brand new pump so you are good. I will find a way to check the vacuum line coming from the pump to see if there is any contamination. Someone on the sprinter forum with the same engine installed a catch for the coolant just in case. Very smart.
I believe there is a separate piece near the WP, a round cylindrical plastic component, that controls the vacuum for the WP (i could be wrong, but i think it's called the changeover valve, see here) that could, or maybe should, be preventively replaced.
I'm old school and not real comfortable around engines where I can't see things or put my hands on them!
Can someone tel me:
1) is this the vacuum hose from the water pump tot he valve? and
2) is this a good place to put the water separator?
TIA!
1) Yes
2) Either where you're pointing at OR in between the WP and the Vacuum control valve ( the 1) in your post). The 1) is the coolant entry point into the vacuum circuit. There are several other components that are tied into the same vacuum circuit, including boost control valves for our sequential twin turbos.
There should be another post on this forum with the vacuum circuit diagram for OM651, which should show you all the vacuum control valves, vacuum tank and anything else tied into this circuit.
What type of water separator were you planning to install? I would be interested in installing it as a preventative measure as well.
#1 is inaccessible. #2 is a lot easier to get at. I suppose I could pull #1 off the valve and tap into it there.
Originally Posted by dzl_benz
There should be another post on this forum with the vacuum circuit diagram for OM651
Thanks. I have a diagram, but was having a tough time relating it to the engine as it is so tightly cowled.
What type of water separator were you planning to install?
Not sure; something simple, just enough to trap any liquid so I can tell what is happening before it damages anything. Maybe adapt a water separator from an air line.
The reason I'm concerned is I had to add about a pint of coolant last winter to keep the "low coolant" warning at bay. No sign of a leak.
2014 GLK350 base model (active) ; 2001 E320 base (retired); 2001 Wrangler soft-top
Originally Posted by John CC
The reason I'm concerned is I had to add about a pint of coolant last winter to keep the "low coolant" warning at bay. No sign of a leak.
Hmmm ... adding coolant suggests there might be a leak. I've seen this on my past vehicles (4 wheel and motorcycles) . What happens is the leak is so small, that the engine bay temp evaporates the leaked coolant , so it never hits the ground. Or accumulates in a v-sump.
#1 is inaccessible. #2 is a lot easier to get at. I suppose I could pull #1 off the valve and tap into it there.
Thanks. I have a diagram, but was having a tough time relating it to the engine as it is so tightly cowled.
Not sure; something simple, just enough to trap any liquid so I can tell what is happening before it damages anything. Maybe adapt a water separator from an air line.
The reason I'm concerned is I had to add about a pint of coolant last winter to keep the "low coolant" warning at bay. No sign of a leak.
I was thinking of adding a small transparent in-line filter just to see if there was any coolant residue. There isn't much space there so hard to find something that is fitting without adding extra plumbing
Definitely check for coolant leak - it is somewhere, especially if you're getting low coolant message! EGR cooler, vacuum tank, thermostat housing around the heating element, shot water pump vacuum jacket, slow external leak - just a few places to name where coolant can escape.
Did the coolant level remain constant when it got warmer?
Yep, I've received that letter earlier this year. Took the Bluetec in to get that software update.
I should also mention I just recently had the OE water pump replaced with the updated metal impeller version, along with new belt, tensioner, idler rollers and coolant.
I think the shop didn't top off the new coolant sufficiently because I could hear some gurgling in the heater core in the dash when it begins to warm up, and also because I got a "Low coolant" warning notice in the cluster the other day.
So I will be topping off with distilled water and then keeping an eye on the level in the expansion tank.
Edit: if coolant leaks out of the new pump and ever finds its way into the engine thus ruining it, I'm assuming (or rather hoping) the AEM extended warranty covers that. It covers a ton of stuff unrelated to emissions anyway.
My Euro Indy did the water pump, coolant, belt and tensioner work, all for $1k; the MB dealer did the software update for free (recall) which doesn’t require them to do anything else with the actual components (so they could’ve been the original ones or replaced); and I made sure the coolant level in the expansion tank was corrected.
Could be coolant cap, heater control valve and those hoses around that, or failing turbo coolant lines. I had a slow leak as well and couldn’t trace it. Ended up replacing cap, and then the heater control valve, it actually failed an I couldn’t get heat, but that wasn’t my source of coolant leak. Ended up being the coolant line for the turbo, left one, it broke on me, the elbow plastic part and I had to tow it home. Replaced that part and my coolant didn’t need to be topped off anymore.
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