Newbie with 300E cooling issues
 

Alright, my grandfather gave me his old '91 300E. It has about 180,000 miles on the odometer, service records going back to 1998, and is cosmetically excellent. However, some difficulties have developed with the cooling system. It has been running a little too hot in traffic for a while now; if it sat too long, temp would rise to perhaps 110 C. Temperature remained, and remains, stable while cruising on the highway at 90-100 C. At the time, I was losing a little coolant, but not so much as to be unmanageable.

However, a few days ago, on arriving at my destination at the end of a long, fast run on the highway, I found a frighteningly large puddle of green coolant under the car. Seems that since then, I cannot keep coolant in the system at all; it is leaking a lot. Also, the overheating has gotten worse. Since I had just moved off to school in Austin, I did not have the time to find an independent or attempt to solve the problem myself. I took it to a dealer (Mercedes-Benz of Georgetown). They replaced the radiator, overflow tank, and upper and lower radiator hoses. This has not solved the problem. What else could be the problem? As much as I hoped the dealer would know what they are doing, it seems to me that they just threw parts at the problem, something I can't afford at dealer labor rates.

Additionally, the engine oil pressure at idle on startup is about 1.5 bar, but drops to about 0.3 bar as the engine heats up. As soon as I tip into the throttle, it jumps up to 3 bar and stays there until I am stopped again. The hot idle oil pressure seems kinda low to me. Otherwise, it seems to be running normally; sometimes slightly rough at idle, but no weird noises, and smooth and powerful at all other engine speeds.

Sorry to introduce myself with such a laundry list of issues. I'm just going crazy, and would appreciate any and all advice you guys could provide.

Thermostat? You know, I just have to ask:rolleyes: Could also be a water pump problem. If you paid more than $150 for the radiator you paid too much... I can do an M103 radiator in about 10 minutes blindfolded... Well, maybe not that quick, but close...;)

Also, your car should not have green coolant if I'm not mistaken it should be clear or transparent... Zerex G05 is what you need bro...

One more thing, the dealer doesn't care about how much money you spend. If your going to have an old car like this 300E, it's time to start learning how to wrench. All the items you just replaced @ the dealer are inexpensive (other than the radiator).

This is a great place to start learning. I learn something new almost everyday around here...


-GH

The thermostat and serpentine v-belt are both new; the water pump was replaced just a few years ago. I know the green coolant isn't right, but I can't imagine topping it off with green coolant caused this problem.

I'm glad the Tstat and belt are taken care of.

I honestly don't think it could be anything other than a water pump at this point. How much coolant will it leak out after being driven? Does it leak at the front of the car? Take it out for a drive and park it, pop the hood and watch carefully at what unfolds. Watch the fittings and make sure they are all tight. Even if your grandfather replaced the pump just a few years ago, it could have certainly failed by now. I have seen stranger things.

A new water pump @ the dealer for your car would likely be $650-750+ installed as the part alone has a list of $368!! It is not really an easy part to get to on your car, kind of a pain in the butt.

The M103 engine also has a habit of blowing head gaskets. Do you know if your car has had this service performed? I know about this problem from experience:( Be careful not to over heat your car as it may damage the head.

Your oil pressure sounds normal to be.

These cars cost money to run. Sometimes a lot of money. One repair can essentially "total" the car. I would kill to have my grandfathers old Benz, what a cool thing to pass down.

Good Luck,

-GH

Two questions. Did the dealer fix the leak? Has the car run hot since the thermostate was replaced? Actually most thermostats fail because the engine ran hot. I have seen many cases where the thermostat was replaced because the engine ran hot, then the real problem was found and the engine still ran hot because the thermostat was damaged when it ran hot before the real problem was repaired. If you can understand the above sentence, your IQ must be 200. In other words, if a thermostate is subjected to a temperature above 120 deg c, then it should be replaced.

Paul

p. rex, the Service Department should never have returned the car to you until they verified the overheating problem was resolved. Take your 300E back to MB of Georgetown, tell them that the overheating issue still exists and you want it repaired properly. I'd question them about their initial diagnosis and replacement of the radiator, hoses and overflow tank. Ask how they determined the water pump and thermostat were OK. With an overheating problem the typical first step would be to replace the thermostat and proceed to replace more expensive parts. I'd press MB of Georgetown very hard to resolve this overheating issue satisfactorily without paying another dime. Overheating issues require someone with experience and diagnostic skills. There are some techs that lack diagnostic ability and simply throw parts at a problem, especially with the older vintage vehicles ... if they can't plug in an electronic analyzer to tell them what to replace they're lost.

Alright, I just talked to them. They said that the overflow cap was also faulty, and replaced it free of charge. They also said that there is a slight head gasket leak (near the back of the engine) that is contributing to my minor oil loss (about 1 quart every 1000 miles), coolant loss, and elevated temperatures in traffic. They said it wasn't completely "blown", and that I could have it replaced when time and finances permitted. Does this make sense?

I wonder whether the new radiator was necessary. I will question them thoroughly, and take it to a good independent next time.

*EDIT* I know the thermostat is good because it was replaced last week; the water pump was replaced within the last year or two, and I would be very surprised if it was the problem. I don't think it is cost effective just to replace it if we have no reason to believe it has failed.

If your head gasket allows oil into the cooling system it might gum up your radiator. This happened to me and I had to buy a new one. Your radiator may have gone bad because of sludge in your cooling system from this head gasket problem.

Keep checking the overflow for crud...

1 quart in 1000 miles is not minor at all in my book:( You need to start saving for the head gasket now, it could give at any time. Keep an eye on the temp whenever you drive it.

So, you believe them that the puddle of coolant came from a faulty radiator cap? I guess it is possible.

I am leaning against a faulty water pump and more towards head gasket failure.

Keep us posted...

Good Luck,


-GH

I should clarify, prior to the replacement of the overflow tank, radiator, and upper and lower radiator hoses, it was losing coolant almost as fast as I could top it back up. Since those items were replaced, I have been losing less coolant, i.e. no huge green puddle, but I am still losing some. I'll see how much of an improvement the replacement of the radiator cap yields. I plan to replace the head gasket within the next year, but can't really afford to spend $1500 right now.

The service manager said that they are quite sure they have found everything, and that it is drivable until I can have the head gasket replaced. He stated that temperature was generally 90-100 C. in normal driving, rising to about 110 C. in stop and go. According to him, this was not a great thing, but acceptable for the time being.

p. rex, your first post mentioned nothing about a leaking head gasket, so I presume the service manager omitted that "minor detail" when describing the repair work they performed on your 300E. Before starting any repair work a responsible servce manager would have mentioned the head gasket problem so you could do a cost/benefit analysis of the total pending repairs. If it were me I'd have the head gasket replaced sooner, rather than later ... before the car leaves you stranded, the inside of the new radiator is sludge-coated, coolant mixes with the oil, etc. With all due respect to the service manager the elevated temperatures he mentions aren't normal in my book. Overheating the engine could warp the head. I presume the new overflow tank is containing most of the coolant that was leaking on the ground, but I would want to know what is still leaking. A large oil leak is a major nuisance and leaves a mess wherever you park.

OK, you want advice, here it is:

Unless you have unlimited funds to throw at mechanics for all the work this car will need over the next few years, get rid of this car and get yourself something reliable and cheap to maintain.

Mercedes are not cheap cars, you can mitigate this somewhat by being very handy and doing the work yourself. From your postings, you appear to be in the position to do neither. This is reality, you need to concentrate on school, not keeping some old car running.

I'm not trying to be cruel, but you need to take the emotion out of this problem, and concentrate on what is important right now, which is getting your degree.

Jim

No, I knew about the head gasket oil leak; sorry I did not mention it initially. At least there is no coolant in the oil or vice-versa; it is leaking oil to the outside, where it is running down the back end of the engine. In response to Jim's comment, sure, I could buy a cheap, trouble-free car if I wanted to spend $5000, but this car was free, and if I can address the problems for that sum of money, I would much rather be driving the w124 than an old Honda. I knew it would be an expensive car to own. I know I am gambling in a way if I pay to have the head gasket replaced, but if I can get this problem fixed, I am willing to deal with $300 spent here and $500 spent there to keep it running the way it should. If I have the head gasket replaced and also a valve job while I am at it, how many other nasty $3,000 problems are left? All I can think of is the automatic transmission, which seems healthy to me.

Anyway, I will pick the car up on Monday and see what I am dealing with.

Well, good luck.

I have a daughter in college, and while I'd like to see her in a Benz (and she would would much rather have hers...), the cost/risk of an older Benz was not worth doing. We have a saying in the nuclear field, "Time, Distance, Shielding.". She doesn't have the time, she is too far away, and I'm interested in shielding myself from downtime and high bills.:)

Instead, I bought a very nice Buick Century with low miles, a car any village blacksmith can fix, and parts generally are ones advertised as "As low as.....". She has to count on the car for work/school and any downtime is costly, so it's a good choice. Running a 180K mile, 15 year old car will require a backup plan and a fair amount of effort from the owner, things that other transportation choices may not demand.

As I said, good luck, I'm sure we all agree these are rewarding cars to drive, and when running well are a joy to own.

Jim

All right, I just got it back, and I made it back across town during rush hour in 100 degree weather. It still heats up a bit if it sits still for too long in traffic, but it stays under 100 C. if I leave the air conditioning off, which is good enough for now.

Time to start saving for the head gasket :D