OM647 Thermostat Replacement

brokengranite

Hold my beer, watch this
Going to replace the thermostat on my 2004 118" this weekend in preparation for a trip to Utah in two weeks.

Ive noticed that it takes 15-20 minutes or so of normal driving for the van to warm up (180F-ish) here in Southern California during the "winter". Ive also noticed that once the van is up to temp, any time theres some sort of downhill where the the load is taken off the engine, the temps drop drastically. From my searching on the forum it seems like a potentially faulty thermostat thats stuck open.

My question is, does anyone have any tips on doing this? Is it relatively straight forward? My plan is to drain the coolant from the radiator into a clean container, replace the thermostat, and refill the coolant from the clean container. We purchased the van about 6 months ago and the coolant was changed not too long before that.

Thanks everyone for all the help from this forum, its a huge resource and glad to see so much love for the T1N.
 
When re-using coolant, I have a habit to pour it through a paint filter (free or cheap from home depot). This step is probably unnecessary but I do find leaves, dirt, etc in the filter after.
 

Zundfolge

1-2-4-5-3
+1 for the above comments. Pull the smaller hose that comes off the water pump manifold to drain enough coolant. Thermostat is at the top so you don't need to drain all coolant. No need to pull a big hose.

Just did this two days ago it happens...

I removed the 3 bolts that hold the metal portion of the fuel lines to various points of the engine bay to allow for some movement in wiggling the thermostat out. Think they secure the return line iirc? Either way. Three bolts in the thermostat. Takes some extensions, I think they're torx. Prepare to be using 1/4" drive stuff. 3/8" drive is too big to get to the bottom bolt.

Could be done in about 30 mins in my opinion.

Another thing, it's possible that your viscous fan clutch is stuck in the always engaged position (or clutch disengaged as it were). Meaning the fan could always be running at full tilt, do you notice a whooshing fan noise always? You could try starting the van cold, roll a newspaper up (unless your news is on an iPad or something, don't do this with an iPad) or a little long roll of cardboard and try to stop the fan blades. If they push the newspaper/cardboard easily away and don't slow, your fan clutch is probably locked up and needs replacing...
 

jrod5150

Member
Bolts are T30. Have a magnet on a stick close to the bolts especially the lower two. If you drop them they always seem to end up in the hardest places to find. I just clamp the upper hoses unless you need a coolant flush.

As the prior repliy states you could have a stuck fan clutch. Youll know once you have the thermostat off, or listen for the constant whirlwind
 
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brokengranite

Hold my beer, watch this
Thanks guys for the tips, my goal was to drain just a little bit of the coolant out from the radiator, I guess I could always pinch off the upper radiator hose and try and catch as much of it as possible in a bucket.

Im fairly positive that I dont have a stuck fan as the engine sounds pretty quiet to me. But Ill double check.
 

white whale

Member
Ive also noticed that once the van is up to temp, any time theres some sort of downhill where the the load is taken off the engine, the temps drop drastically. From my searching on the forum it seems like a potentially faulty thermostat thats stuck open.

.
maybe experts can chime in, I thought the temp swings were part of the engine characteristics.
I've had that since day one - more so in cold temps. Mine has recently stopped the really big swings and is staying higher than what it used to be on the hill climbs. Looking to change mine out now for that reason.
 

brokengranite

Hold my beer, watch this
Thanks guys for the tips. I got around to doing the thermostat this morning. About an hour all said and done. I pinched the upper radiator hose and tried to catch as much coolant as possible but once I unbolted the thermostat, lost some more. Added about 1/2 gallon of distilled water.

The job was fairly straight forward, I used a 1/4” T30 and multiple extensions. Two are pretty easy to get to, the right one is a little more difficult. Didn’t unbolt anything or remove the oil filter cap. Only removed the turbo hose to give myself a little more room.

The weird part, once I got the old thermostat off I was looking forward to seeing a stuck open valve, but was disappointed to see it looked just like the new one. I replaced it with the new one and buttoned everything up and took it for a test drive. It was 55F outside, and after about 5 minutes of driving, i was right about 180. Which seemed much faster than in the past. I’ll have a better idea tomorrow on my drive to work if the new thermostat fixed anything.

https://flic.kr/p/2iwUd3G
 

brokengranite

Hold my beer, watch this
Throw the old one in a pan of water and heat it to see what it does.
Thats next on the list!

Drove to work today and it was up to 180 in about 4 miles of driving side streets. Outside temps were 52F-55F, was hoping it was going to be colder to have better testing conditions. We'll definitely know if its fixed once we get into Utah in two weeks.
 

jrod5150

Member
Thanks guys for the tips. I got around to doing the thermostat this morning. About an hour all said and done. I pinched the upper radiator hose and tried to catch as much coolant as possible but once I unbolted the thermostat, lost some more. Added about 1/2 gallon of distilled water.

The job was fairly straight forward, I used a 1/4” T30 and multiple extensions. Two are pretty easy to get to, the right one is a little more difficult. Didn’t unbolt anything or remove the oil filter cap. Only removed the turbo hose to give myself a little more room.

The weird part, once I got the old thermostat off I was looking forward to seeing a stuck open valve, but was disappointed to see it looked just like the new one. I replaced it with the new one and buttoned everything up and took it for a test drive. It was 55F outside, and after about 5 minutes of driving, i was right about 180. Which seemed much faster than in the past. I’ll have a better idea tomorrow on my drive to work if the new thermostat fixed anything.

https://flic.kr/p/2iwUd3G
Its really hard to say because yours didnt seem like it was 100% faulty from your description. Ive had them so bad that they never pass the first notch on the gauge even after a 30 minute drive . Ones that are that bad you can see the rubber seal pieces visually missing when you remove the stat. Yours was probably just starting to internally leak.
 

brokengranite

Hold my beer, watch this
Its really hard to say because yours didnt seem like it was 100% faulty from your description. Ive had them so bad that they never pass the first notch on the gauge even after a 30 minute drive . Ones that are that bad you can see the rubber seal pieces visually missing when you remove the stat. Yours was probably just starting to internally leak.
Back from our Utah trip and the van ran great. The van would get up to 180 within 5 miles or so even in the 30's after a cold night at camp. Really happy that it was an easy fix. Thanks everyone for the help.
 

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