Hey everyone, just picked up a 1991 190E with about ~100k miles.

The last owner told me a lot of stuff was replaced already and included all of the receipts of the work. The water pump was replaced about 2 years ago (~15k miles).

Upon bringing it home, I took the bottom plastic guard off and noticed that some coolant was pooled up in it. It looks fairly fresh, very green and couldn't notice much oil other then residue thats been caked onto it.

Suspecting a leak, I left the cover off and ran the car for a little and drove it around the block. It never got close to overheating, It would hit the "80" mark on the thermostat and just about hover there, going slightly over if I let the car sit without moving. Fans always kicked on and off.

I checked under neath the car when I got home and noticed a decent drip of green coolant coming from the oil pan. Didn't notice any oil mixed in, but it seemed to be dripping from the oil pan bolts.

Raised her up and tried to clean as much as I could underneath to find the source of the leak, there was a decent amount of oil residue and coolant in places but I'm assuming this has been missed from the previous owner.

I decided to wrench the oil pan bolts a bit tighter, some were snug but others I could tighten a little bit with mild force. Wiped down everything again and decided to run the car again and go drive it around for ~10 minutes.

Ran the heat on high for some time also.

Upon getting back home, there seemed to be absolutely no coolant leaking from the oil pan anymore. Before it was a somewhat steady drip as the car was hot and stopped when it cooled. This time, there was nothing. However, I could notice a faint coolant burn (sweet smell) but not sure if this was just residual coolant left that was burning off or if tightening the bolts caused the coolant out somewhere else?

I suspect it's the water pump (or was?) but really have no experience with these cars or engines so just looking for some insight.

TL;DR = Was dripping coolant from oil pan/oil pan bolts, tighten the oil pan bolts and now it's not leaking anymore, but could smell a slight coolant burn sweet smell after driving around.

Well first things first is get that green crap out of there right away. Drain, fill with water, drive, drain, fill, keep going until its almost gone and refill with 50/50 Distilled and Zerex G-05, or the latest MB (blue I believe). Both are suitable. Green is NOT and will corrode.

If its life has been with green junk, possibility that engine gallery plugs are corroded if the coolant is coming from the block. I'd bet you'll find rust in the system due to the green coolant used. A system used with correct coolant will essentially never show anything but a smudge of orange tint.

__________________
2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

ahhh I did not know that, It's not diesel btw. Does that matter?

It's very likely your water pump and dripping down to your pan. The other suspects are the heater hoses.
That's bull ****.

The color of the coolant is determined by whatever dye the manufacturer decided to put in it. The only thing that matters is that it's aluminum safe which every coolant on the market is today. There's nothing special or about the metals, gaskets and plastics found in a Mercedes cooling system. Just flush it out every 2 years.

__________________
CENSORED due to not family friendly words

I think you may be right.

After further inspection of my 2nd drive today, there was a little coolant leaking down but not as much. I'm going to try and do a full engine clean up today from the top down and see if I can find the source around the water pump.

Are they hard to change in the 2.3 or would I just be better off finding a garage to do it? Money isn't really an issue but I just want it done right

It’s true the color of the coolant isn’t a giveaway, but the coolants themselves have differences. See this below experiment. I stick with MB spec under the assumption it was tested on our engines, and because I got a coolant pump shaft leak shortly after refilling with generic green stuff. Coincidence or something more (scary music)?

https://www.audizine.com/forum/showthread.php/263790-Antifreeze-Experiment-amp-Testing

__________________
Prost!

I was unaware that the typical green-stuff wasn't the norm in these cars, however it's just what was in it when I bought it. Coolant looks very new and clean, but I'm the kind of person who would prefer to stick with the safest choice and I think OEM will give me little bit more peace of mind. Considering the fact that the water pump wasn't changed too long ago and issues are arising already.

My 2.3 has been running generic green coolant for decades on the original water pump. Doesn't leak a drop. I've got whatever green coolant was cheapest in the m102, m112 om603 and om606. The only water pump failure I experienced was the om606 shortly after I bought it at 220k miles. It had the blue stuff in it but I doubt it had anything to do with the coolant. The shortly there after I preventatively replaced the om603 pump at 230k miles.

Every Euro manufacturer has its own preferred coolant that a small kabal of owners swear by. Volvo's, BMW, VWs etc all do it. It's a weird cult think I'm never going to understand. Heaven forbid you try to put Mercedes coolant in an Audi or vice versa. They'll skin you alive. All cars use the same metals, seals plastics in the cooling system. There's no unobtanium in any of them.

If only putting Mercedes coolant in your Mercedes gets your rocks off, more power to you. But don't spread misinformation or lies because someone used green coolant in their car.

__________________
CENSORED due to not family friendly words

As I mentioned above, the 190e doesn't even come close to overheating which makes me suspect that the water pump (which is fairly new) is working correctly but possibly it's just not sealed correctly?

It only drips when the car heats up. I'm currently away from my car at the moment but is it possible to just tighten up / check the water pump bolts without dissembling much?

The water pump shaft has a weep hole on the underside. Take a close look at that spot. Otherwise I would inspect all the hose connections.

__________________
CENSORED due to not family friendly words

So upon further inspection after cleaning from the top down, I noticed a loose bolt on the water pump, one right behind the fan pulley.

It appears to be stripped as it won't tighten at all and seems to be the source of the small drip.

I'm actually glad I found the source, it's just a small leak but everything else operates correctly. I may dab some jb weld in the area rather than go through pulling the entire thing and see how that works or just live with the slight drip.

If it's a stripped bolt hole, you'll have to helicoil it to fix it right. Another possibility is that the wrong bolt has been installed during a replacement, was too short by a little bit, only engaged a few threads, and pulled those out when tightened. That's easy to check by removing the bolt, sticking a length of wire into the hole to measure depth of the hole, then comparing to bolt length. General rule is 1 1/2-2 times bolt diameter for thread engagement. An 8mm bolt should have 12-16mm (1/2" to 5/8", roughly) of thread engaged. If the bolt was 4mm short, it could easily pull the first few threads out when torqued to spec, or just under "feels right" tightening.

If only I could, the bolt is completely loose but I can't get it fully out because it hits the back of the pulley, unfortunately. I'd have to disassemble it all just to check which I just don't have the worries to do at the moment