My 1995 E420 is barely getting to 75 degrees C after driving 45 minutes to work. I'm in maryland, where mornings have been right around freezing.

How hard of a job is it to replace the thermostat? SHould I just get a stock thermostat or is there some specific temperature setting I should be looking at?

I'm a reasonably good DIYer, so I'd like to keep it out of the shop for this one.

Thanks,
Troy
1995 E420 105k

Could be a bad sending unit, or a bad gauge, or could be nothing wrong at all. I will often run around 80 in cooler weather but that's in AZ.

If the temp gauge is correct, you NEED a new thermostat. Go with the stock one, which is an 87C thermostat. This means it starts to open at 87C and will be fully open at 102C. As the thermostats age, they start to open at cooler temps. If you are running at 75C, a new thermostat should bring you back above 85C, where the temp should be.

Overall, it is an easy DIY job.

__________________
Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record

Y2kimmel

Funny you should ask - I replaced mine two weeks ago (1995 E420) for exactly the same reason.

Here's what you need to know:

- you need to drain the cooling system down about 6 liters to do it. I inserted a piece of pvc tubing in through the coolant header tank and down into the bottom hose that goes to the bottom of the radiator. It was a breeze to siphon the coolant out, and it precludes removing the bottom engine cover.

- take your VIN and engine serial number and get a new thermostat from the dealer. Depending on your VIN/engine number, there's an "early" type or a "late" type of thermostat. Early looks like a regular thermostat, and you remove the cover/hose connection to get at it. Late is built right into the cover and hose connection, it's all one unit. Mine was "late" but less than 100 after the change over of production.

- get a new hose elbow. Mine was in good shape, but for $7 (or so) I just don't want to bother not replacing it.

- removing the thermostat housing is "relatively" easy. After draining the coolant, remove the hose. It comes off once you remove the clamps and loosen it from the aluminum that it's been attached to for a decade. DON'T scratch the fittings!!! I was replacing the housing, so I let it get damaged, but I was careful with the one that was staying in place.

- two of the three t-stat bolts (my kit came with new ones and a new o-ring seal for the t-stat itself) are easy to remove. The one at the back is a b***h and there's no other word for it.

- To reach the back bolt, undo the allen-head bolt that holds the dipstick tube bracket in place. Move the dipstick tube as far up and as far away from the t-stat as you can (not very far, though, as you'll see). In a perfect world, you'd be removing the spark-plug wiring loom from top front of the intake manifold and pulling the dipstick tube right out. If you damage the o-ring at the bottom of the tube, you might have to do that anyway.

- now that you've created a tiny working space around the back bolt, use a 1/4 inch drive 10mm standard socket and a 1/4 flex handle (there's no room for a ratchet head, but the flex handle head will just fit between the dipstick tube and the top of the socket on the head of the bolt) to loosen the bolt so you can unscrew it.

- I unscrewed it with a universal joint plugged into the socket (a one-piece u-joint socket would be best but I didn't have one).

- once you have it out, replace the t-stat (the easy part) and put it back together. Assembly is the reverse of disassembly, and the dipstick tube will still be in the way of the back bolt.

The last bit of fun is installing the short rubber elbow. Once the plumbing is bolted back together, the rubber tube has to be lubed (with coolant) and slipped into place. It only took me about 1/2 hour of twisting and swearing, but it finally popped into place.

Refilling the coolant is not a problem - mine was "full" at about 3 liters put back, and after the engine warmed up I got another liter in, and after a short drive on some hills, the light came on and I got the last of it in. It takes a while to fully "burp".

All in all it's not a bad job, and without the dipstick tube issue, it literally could be done in 1/2 hour. Mine took nearly three hours as I was trying to figure out how to do it, and which tools fit and which didn't. Having done it I wouldn't hesitate to do it again.

I hope that you find this useful!

Cheers
JJ

I looked at the temp gauge in the car again - the temp is not getting much above 60C on even medium-duration trips, and the fuel economy is really taking a hit.

I'll replace the thermostat soon - JJ thanks for that great write-up. If you ever need to remove the valve covers on the same engine, please don't hesitate to ask for help. Lots of little helpful hints, that i unfortunately had to learn along the way, will help turn it from an all-day job to a few hours.

Troy
1995 E420 105k

I did it myself a few years ago and I replaced my 87C tstat w/ an 80C version. When I removed the old one, it was 'stuck' open so that explained why my car took a long time to warm up. Now it warms up w/ 5 mins or so.

That short rubber elbow . . . it still can get my BP up just thinking about it! I didn't lube the rubber and you can get a picture of how hard it was to get on w/o 'lube'.

After I did get it on, after many scraped knuckles! Later when I was at my tech's shop (Exclusive Motors), he was replacing a water pump. When he came to replace the elbow, he, of course, lubed it . . . and . . . used a small right angle 'tool' that he could reach around the back side, grab the backside, and slide the %#*^@! on within two seconds and no scraped knuckles! Live and learn I always say!

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

I just finished this job last week. I did little homework on this because I figured there couldn't be anything to it, so I didn't find this old thread until I was already in trouble. If you're about to do it, here's what I can add.

I had the new part in a box, which I didn't open before starting the job. Big mistake. If I had looked at it I would have seen that the thermostat is part of the housing, and I would have realized that it is side mounted rather than top mounted. The only homework I did was looking at the Part Explosion diagram on Alldata, which is flat out wrong. Had I looked at the Thermosat Service and Repair section (also not quite right), I might have done better.

The reason this matters is that the top housing (which looks like every other thermostat housing in the world) is empty. I actually stood there for a few minutes trying to figure out what happened to my thermostat when I opened it up. I needed to buy another seal and a short hose to put this thing back together. While taking it off, I also snapped off the top of my dipstick (I thought that had to be a first, but, incredibly, a guy over on Benzworld had done the same thing.) Total waste: $26.

To do this you have to get the engine cover off, and get the serpentine belt out of the way (because you can't get the thermostat past it unless it's off the top pulleys). Disconnect the dipstick tube, and use cable ties to cinch it over toward the fuel rail, giving you the most direct access to the famous back bolt. Just cut off the old hose (it costs $23.50, on top of $47.50 for the stat).

Now it's time to stuff rags in all of the spots where you can drop wrenches and other tools. But have one of those long retrieval magnets on hand just in case. I used 1/4 inch 10mm socket to get the first 2 bolts out. I couldn't get the third though. I tried a u-joint with my socket, but I could not get it. I went out and bought a set of flex head ratcheting wrenches, but it just couldn't swing enough to work. I then went and got a flex head 1/4 inch socket that did the trick, with about a two inch extension.

Even though I did the same procedure on the GMC Jimmy a couple months back for the same reason (stat stuck open), I should have known better than to think I could mindlessly do it on an MB. I wound up making two extra trips for tools, and two extra parts counter runs, which made this a lot more expensive than letting the dealer do it.

__________________
1996 C280 289K Traded
1997 E420 167K Traded
2001 S430 240K Traded
2010 E550 4matic 80K
2000 GMC Jimmy 198K Gone to Boneyard
2003 Camry LE 196K
2011 Mazda3 i Sport 31K