Some time ago I found a nice blow-by-blow description of how to change the t-stat on a 603 ... can't find it now. Can someone give me a step-by-step description for doing that job? I'm not sure if it's one I can do on my own, but I have the new t-stat and thought I might try the job.

Is this job at all idiot-proof? What things do I need to look out for or be prepared for?

Starting mid-week I'll have a second car (yes, the Liberty CRD is joining my stable), so I can actually do jobs on the MB without worrying about having it up and running to go to work at 4 p.m. every day.

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)

Really all you have to do is remove the housing. It's held on by 3 10mm bolts. However, it looks to be a pain with all the other parts in the way. (I have my turbo off so it would be REALLY easy for me to do, but it works fine so fine it stays. I would think you can manage it. I think if you just take your time you can just undo the bolts and remove. Remember though, the new t-stat goes in like the old one, with I believe the spring facing out. What makes you believe you need a t-stat?

Thanks
David

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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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It has been running a tad on the hot side ... tends to approach 100 on warm days during my somewhat trafficy commute to work. It isn't "overheating" or doing anything particularly alarming, but the frequency with which it would creep to 100 was a little concerning to me, so I spoke to my very trusted mechanic (in addition to the, as always, helpful advice I got here). As usual, he didn't try to cram unnecessary work down my throat, but did recommend changing the t-stat. He said it wasn't likely the cause (that more likely, the running temps are just a reaction of the hilly area + lots of stop lights), but that since I brought it up, it would be a good idea to replace the t-stat regardless. I looked back over the records and it's still the original unit in there as far as I can see. So for $25, if I can do that myself, I figured it wouldn't hurt as preventative maintenance.

Interestingly, since I purchased the t-stat, it's been running much cooler ... even though it's sitting on the floor of my living room ...

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)

I know what you mean with something working when the replacement is ready. However, I doubt your thermostat is the problem. Does your cooling fan come on as it should? I'll bet that what you're experiencing is perfectly normal. How about a coolant flush? I hope I'm not beating a dead horse, but I'd search for 603 fan clutch. In fact I'll look into diagnosing a fan clutch now, because they can be very tricky to diagnose.

Thanks
David

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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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To check the fan clutch, with the engine off, it should not spin easily by your finger with the engine hot. I believe this is how you could check it. You shouldn't be able to just throw it around and have it do a complete circle.

Under what conditions is your car gettign up to 100C? You know many other member report the same thing even after they spend close to $1k on their cooling systems? Clean out your radiator and do a good flush, even try a flushing agent and I think that will lower your temps some. I am in the process of flushing my SDL now, though the day after the cleaning agent was in it had to be taken down for a week. The stuff I bought it the Prestone FLushing Agent and I'm going to run it 400 miles or so with just water then flush some more before topping off with coolant. If you want specifics about coolant flushing, you can do a search under my name and coolant flush. If I lived closer I'd do it for a Pepsi. (I work cheap)

Since you already have the thermostat, have you looked at the right side of your engine (from the inside, directions are always taken as if you were in the car) to see where the housing is? I'll take a picture of mine today when I'm up working on it (the car is 25 miles away at work).

Thanks
David

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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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This one does the same thing.

I agree with the mechanic.

If it ain't broke, don't fix it.
...........PEH, 1972...........

The thermostat is a real PITA. You must remove the intake duct for the turbo and do most of the job by feel, no room.

However, your problem isn't the thermostat, it's probably the visco clutch.

Idle the engine until the temp guage goes up to 100 or so and watch the fan while you shut the engine off with the stop lever. Fan must not spin more than one revolution after the engine stops, and it must be pulling large amounts of air (roaring). Must also roar for a second or so when first started.

If the fan spins more than one revolution after engine stops, the visco clutch is empty and nonfunctional. Replace it and your temps will drop to just above 80 and stay there.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

T-stats are a bi metal and last a very long time. Their really isn'y anything to break.

I'd start with flushing your cooling system and cleaning out the radiator. However if it is old for $20 it couldn't hurt.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

I'll check the clutch as described ... see if that's the issue. Maybe my dad can help me do a coolant flush when I'm home over the next couple days (sounds like something I'd rather do with a wingman than flying solo), and while I'm in there I can throw in the new t-stat. Not that I want to just replace things willy-nilly in a paranoid frenzy, but I feel as though I'd rather play it on the $20-safe side than have the old one get stuck shut and find out it's tired that way.

Of course, naturally, now that I've come up with a plan of attack, the car hasn't gone near 100. Go figure.

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)

As I understand it, it wasn't so much a breaking issue as getting stuck, either shut or open. I believe this is also what my mechanic was telling me ... there is always a little doubt because he has quite an Italian accent. That, combined with my lack of speed in comprehending conversational speech, causes the occasional confusion ...

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)

You need a fine tooth ratchet. One of the bolts is easier to get to from below.

If you want to experiment with the fan clutch before buying a new one...

300SDL revitalized clutch fan

Sixto
95 S420
87 300SDL

Here's a picture of the thermostat housing in my SDL. Now, picture a turbo and all intake piping there, do you still want to try this if you're unsure? I have it all apart for my ever-growing exhaust repair.

Thanks
David

Attached Thumbnails

 

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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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I don't know how much room the W124 has but it was childs play on the W126. Two bolts simple to get at, in and out. Just make sure to clean out the old gasket. I had my radiator, lower hose, and fan out though.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

It's a bit of a pain on the w124! You have to remove the boot between the turbo and MAF, and I also had to remove the sensor immediately in front of the housing (22mm offset box wrench). You have to make sure that you align the little tab inside the housing with the recess in the thermostat, or everything will appear to bolt up fine, but it will leak. I made the mistake of assuming that the check valve needed to be at 12 o'clock. It definety isn't. Please don't install it 4 times, thinking you may have a cracked housing or worse. Look for the little tab!
Hahn Rossman
www.alkifoundry.com
1981 TD
1987 TD