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Old 08-22-2010, 04:11 AM   #1
hkpierce
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Default Thermostat change OM612

On my recent run through the Rockies, my 2002 ran hot - much different from previous trips; and then on down-hills it would go below 180. So, I guessed that the thermostat was stuck in some intermediate position. After I did the removal described below, I did not see any problem with the old thermostat - and went on to check the radiator.

My 2003 Service Manual is of no use for my OM612, and, it has turned out, implies that the thermostat replacement is fairly easy. Maybe for the OM647s, but NOT for the OM612s.

First, I note the suppliers are all within $10 of each other. I used Berry for $63.50 (including gasket and new temperature sensor) plus $10.00 shipping. If you need about 500, they are available for $2.21 (without gasket and sensor) plus shipping:
Sprinter Thermo.JPG

Berry's: Note that the Chinese supplier's picture and the parts catalog agree, whereas the Berry actual product is different in that it lacks the optional feed line from the bottom. This is a GOOD improvement as we will see later. The Wager thermostat is set for 87 degrees C.
P8171501.JPG


On the OM612, to gain access to the 3 Torx screws holding on the thermostat, the upper radiator and overflow hoses and the air feed hose have to be moved, and the oil filter cap (and filter) removed. Put a rag in the canister to prevent trash from falling in. Did this help? Yes - it prevented a screw from falling in. But I still lost a screw somewhere. It is almost impossible to manage the screws when pulling them out.
P8211615.JPG

Oh oh. The thermostat is now lose, but it is encased by the manifold in the back, the right and above, the head to the left, fuel lines to the front, under and to the right, and electrical lines on the top. It is trapped.

P8211617.JPG

The main impediment is the steel high pressure fuel line. To get access to that line, the vacuum line and the two low pressure plastic fuel lines have to be removed. As you already know, 612s hate losing their prime. It is so demoralizing to listen to the prime being lost on this maneuver.

P8211619.JPG

Last edited by hkpierce; 08-27-2010 at 02:41 AM.
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Old 08-23-2010, 12:07 AM   #2
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Default Re: Thermostat change OM612

The new and old styles. The old thermostat showed no signs of corrosion or anything else.

P8211620.JPG

The protection sleeve around the fuel line had worn through. Trouble waiting to happen. I rotated the protective casing.
P8221621.JPG

With a little wiggling, the new thermostat slid into position. I replace the original Torx bolts with hex bolts (visible at the bottom of the new housing). Much easier to control.

Many of the clips were brittle and broke. I used nylon ties to clamp lines down.
P8221622.JPG


This was not technically challenging; but it took forever not including the reprime. Depending on what the mechanics charge, this may be one job where it is cheaper for them to do it.

Last edited by hkpierce; 08-23-2010 at 01:02 AM.
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Old 08-27-2010, 02:33 AM   #3
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Default Re: Thermostat change OM612

HK,
another great Write-up. I hope you're correct about the OM647, which I have, being easier.

You mentioned hex head cap screws... I've changed a few different non-critical fasteners over from Torx for the reason you mention. Near blasphemy to the Sprinter purist I imagine.

Is the Wager (Wagner?) 87C stat setting different from all the others?

Nice use of cable ties. Would a couple properly placed ties keep the fuel line from rubbing where you rotated the casing? vic
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Old 08-27-2010, 02:45 AM   #4
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Default Re: Thermostat change OM612

Quote:
Originally Posted by Aqua Puttana View Post

Is the Wager (Wagner?) 87C stat setting different from all the others?

Nice use of cable ties. Would a couple properly placed ties keep the fuel line from rubbing where you rotated the casing? vic
The thermostat part is the same for both the 612s and 647s, so the temperature setting would be the same.

Re the fuel line and ties - surprisingly NO. That line is wedged between the thermostat housing and the manifold, with very little wiggle room.

Last edited by hkpierce; 09-07-2010 at 10:49 PM.
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Old 11-04-2010, 10:16 AM   #5
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Default Re: Thermostat change OM612

Firstly let me thank you for your detailed post especially the photos. They helped me locate the thermostat even though my engine is different. I also had overheating problems in the warmer weather in a Sprinter with the 313 CDI motor coupled to manual gearbox ( so no auto fluid cooling is done by the radiator, the gearbox oil has its own separate external cooler.) Last summer I replaced the thermo coupling on the fan with a new genuine part but it made little difference in the engine coolant temp. My problem was a rapid increase in engine temp when climbing hills. Selection of a lower gear and holding the RPM to 3000 slowed the increase in temp and avoided overheating.

This week I installed a new radiator and put the old thermo coupling back after adding 15 Mls of Toyota silicone oil to help it work better.

Over the last three days the engine temp is 40 degrees only rising to a maximum of 55 degrees when pushed hard up a hill. The cabin heater is now not working.

I am looking at the thermostat as the next possible avenue of attack. From your pictures I could not tell if the thermostat is encased in the housing or could the previous owner of my van removed it in an effort to control the engine temps?
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Old 11-04-2010, 10:39 AM   #6
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Default Re: Thermostat change OM612

Quote:
Originally Posted by glenview265 View Post
Firstly let me thank you for your detailed post especially the photos. They helped me locate the thermostat even though my engine is different. I also had overheating problems in the warmer weather in a Sprinter with the 313 CDI motor coupled to manual gearbox ( so no auto fluid cooling is done by the radiator, the gearbox oil has its own separate external cooler.) Last summer I replaced the thermo coupling on the fan with a new genuine part but it made little difference in the engine coolant temp. My problem was a rapid increase in engine temp when climbing hills. Selection of a lower gear and holding the RPM to 3000 slowed the increase in temp and avoided overheating.

This week I installed a new radiator and put the old thermo coupling back after adding 15 Mls of Toyota silicone oil to help it work better.

Over the last three days the engine temp is 40 degrees only rising to a maximum of 55 degrees when pushed hard up a hill. The cabin heater is now not working.

I am looking at the thermostat as the next possible avenue of attack. From your pictures I could not tell if the thermostat is encased in the housing or could the previous owner of my van removed it in an effort to control the engine temps?
313 CDi : Anti corrosion Coolant Part number MB Sheet 235/MB A000 989 08 25 10
Change every two years Your temp will never exceed 85c average 80 C at 45c F out side ambient temperature.
Protected to -35c Three 1.5 litre bottles required.
If you use a high grade 0W-40 Supersyn oil MB229.3/ 229.5 Your top end operating temperature will reduce, radiator temp increase.
Manual trans mission oil MB Sheet 235.10 MB A 00 989 26 03 10/ two bottles required 1.06 liters. Total required 1.5 liters. or thereabouts.
Richard
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Old 10-26-2014, 05:02 AM   #7
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Default Re: Thermostat change OM612

Quote:
Originally Posted by hkpierce View Post

The main impediment is the steel high pressure fuel line. To get access to that line, the vacuum line and the two low pressure plastic fuel lines have to be removed. As you already know, 612s hate losing their prime. It is so demoralizing to listen to the prime being lost on this maneuver.
Just replaced my OM612 thermostat, and it is, indeed, far from easy. However, I was able to replace mine without disconnecting the low-pressure fuel lines, and thus maintained the engine's prime. By removing the accessible Torx bolt on the engine lifting bracket just above the thermostat and then loosening the high pressure fuel line at the pump, I was able to gain just enough clearance to finesse the old thermostat out. The new model thermostat goes in far more easily.

On another note, I ordered my thermostat from my local independent parts store. Stant was the brand on the box, but when I opened it the part was marked Wahler.
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Old 03-28-2017, 05:22 PM   #8
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Default Re: Thermostat change OM612

What size hex screws did you replace the torx with? Im about to do this job, and cant seem to find the bolt size anywhere.

thanks
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Old 03-28-2017, 07:32 PM   #9
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Default Re: Thermostat change OM612

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What size hex screws did you replace the torx with? Im about to do this job, and cant seem to find the bolt size anywhere.

thanks
I don't remember. I took one of the bolts to the local hardware store and found a metric bolt of the same length and pitch.
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Old 11-01-2019, 07:14 PM   #10
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Default Re: Thermostat change OM612

Bump this to ask - is the 647 changeout sort of dummy proof then? Looks easy on the surface - 3 bolts, or am i missing something? Could not find mention on the difference to this thread. My parts jobber has a Mahle brand for $100. China knocking these out for $1 a piece is scarry via the OP. Counterfeit auto parts is an easy story to believe.
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