Help with my '87 Benz 300E...

There are a lot of car guys here so I thought I'd ask here rather than go to the myriad of Benz forums. I have an '87 Benz 300E (W124 body) that I use as my commuting car. It has about 90,000 miles, I've owned it 2 years, got it cheap and is perfect for it's purpose. The problem I am having is with the anitfreeze/coolant system. I get the coolant light on the dashboard, fill up the reservoir tank, light goes off and then it promptly comes back on (after about 5 miles). The coolant level in the reservoir goes down, but not like it's leaking anywhere. There is no coolant on the ground. Right now, the coolant level is adequate, maybe a bit low but the light is still on. Also, the coolant temp gauge goes from 0-120 degrees in about 5-10 minutes of the car running. There was a crack in the thermostat head cover that was letting out coolant, but I replaced that. Also, when the temp gauge goes as high as it can, in the two front heating/cooling vents on the dashboard, you hear a boiling liquid sound. There is some liquid swishing in there (coolant?) that starts to boil when the car gets hot. Any ideas what I should check for?

I know I can take it to a mechanic and I probably will but I am using this car as my guinea pig to learn about car engines, repairs etc. (it's also my "bad weather shoes" equivalent as I don't really care what happens to it, like when you are coming off the exit ramp on the Palisades Pkwy, dooze off and side swipe the guard rail). Also, the car was cheap and I've put about 2K in it so I don't want to spend a whole lot more than it's worth.

Sounds like your coolant goes into your heater core which is normal when you have the heat on but proably is not suppose to happen when the heat is off. If you put your heater on do you get a coolant smell inside the car? Does the car get white smoke coming out of the tailpipe? If it does it would indicate coolant burning inside the engine. Does the car overheat or does it stay in normal temperature range? Does the temperature gage drop when you drive on the highway as opposed in the city?

This is just a shot in the dark, but you may have a minor leak somewhere that is just enough to leak the coolant but not that much that it will not evaporate. If it is an old car, could definitely be cracked hoses. Happens much more often here in Arizona of course, with the heat that makes rubber such as tyres and hoses in to jerky. Could even be a small radiator leak somewhere. If you look at the engine compartment around the cooling system, do you see any discoulouration that would look like it was caused by the coolant?

Originally Posted by edmorel

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The problem I am having is with the anitfreeze/coolant system. I get the coolant light on the dashboard, fill up the reservoir tank, light goes off and then it promptly comes back on (after about 5 miles). The coolant level in the reservoir goes down, but not like it's leaking anywhere. There is no coolant on the ground. Right now, the coolant level is adequate, maybe a bit low but the light is still on. Also, the coolant temp gauge goes from 0-120 degrees in about 5-10 minutes of the car running. There was a crack in the thermostat head cover that was letting out coolant, but I replaced that. Also, when the temp gauge goes as high as it can, in the two front heating/cooling vents on the dashboard, you hear a boiling liquid sound. There is some liquid swishing in there (coolant?) that starts to boil when the car gets hot. Any ideas what I should check for?

Ed, check your oil dipstick. Hopefully, the oil is not a caramel or cream color. This sounds like your leak could be the head gasket, the coolant could actually be leaking into the engine block where the oil is (undetectible by you). This is a very common, and some what costly, issue with many older cars. When detergents in oil come into contact with coolant/water they turn white, if the problem is severe you will know by the coloring.

Even if you can not see a change in the oil color, I would have it checked out as this can ruin an engine by warping the heads when the car over heats. Good luck.

Clarify: Three problems, am I right? 1) the car is overheating, and badly, 2) low coolant light, and 3) there is a leak beacuase the level is not maintained

I'm not sure if you have all three, but here are some thoughts.

To follow up on Laguna, anything that looks vaguely mayonnaise-like in the oil filler or on the dipstick would also indicate coolant in your oil. Conversely (and rarely), looking for a thin film of oil in the coolant expansion reservoir is also worthwhile.

Additionally, (this happens with some cars more than others, and I don't know your engine at all), some cooling systems are susceptible to getting air entrained in the system and have a specific procedure for getting all the bubbles out -- which you may need to follow. An air bubble in the cooling system tends to create a big hotspot, and that spot can get sufficiently hot to wreck the component it's on.

Depending on where the heater core is leaking, you could be dumping coolant into your body panels under the dash, where you might not see it -- insulation and stuff can absorb it. Do you smell any coolant? Further, if your gauge is maxing out, you're at the engine damage range, and that's real bad -- don't let that happen! Even during diagnostics!

Other things...look for corrosion at all the fittings, and everywhere on the radiator. Sniff the engine and the vents -- coolant is a burning, rotting fruit smell when it flashes to vapor. Check for damp air from the heating system.

~ Huntsman

Could be the water pump, they don't last forever. Please get it checked out soon. That car will easily do 300K+ miles. Mid-90s and newer MBs are trash, keep the good ones on the road.

Thanks guys. I will check the things mentioned, particularly the water pump. The car coolant temp maxes out within 5-10 minutes of driving the car and I would swear that there is coolant swishing around in my two front dashboard air vents. When the temp maxes out, the radiator fan comes on and you hear a boiling sound in the dashboard air vents. interestingly enough, the coolant level has been about the same for the last few days, but the light still comes on.

Originally Posted by edmorel

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Thanks guys. I will check the things mentioned, particularly the water pump. The car coolant temp maxes out within 5-10 minutes of driving the car and I would swear that there is coolant swishing around in my two front dashboard air vents. When the temp maxes out, the radiator fan comes on and you hear a boiling sound in the dashboard air vents. interestingly enough, the coolant level has been about the same for the last few days, but the light still comes on.

Ed,

if you come, to Mr Bodner's this, weekend, we can take out the engine, togeather. I'll speak with, Hector.

Originally Posted by vaclava krishna

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Ed, if you come, to Mr Bodner's this, weekend, we can take out the engine, togeather. I'll speak with, Hector.
Do you, when working on car, wear coveralls, of the tweed?

Ed, how many miles on that baby? I'm looking into picking up a mid-late '80's Benz in a couple years. Bad idea for a 20-something?

Originally Posted by Connemara

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Do you, when working on car, wear coveralls, of the tweed?


For the summer , I wear a tweed speedy, which doesn't cover, all.

Originally Posted by edmorel

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Thanks guys. I will check the things mentioned, particularly the water pump. The car coolant temp maxes out within 5-10 minutes of driving the car and I would swear that there is coolant swishing around in my two front dashboard air vents. When the temp maxes out, the radiator fan comes on and you hear a boiling sound in the dashboard air vents. interestingly enough, the coolant level has been about the same for the last few days, but the light still comes on.

In light of additional information thought I add another 5 cents.

Since the temperature maxes out so quickly I would say the coolant is not being circulated through the radiator. That could be because the water pump is shot, the thermostat is stock in a closed position or a piece of debris is blocking some passageway. When the car overheats you can carefully check to see if the radiator feels hot.

Originally Posted by Dmax

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In light of additional information thought I add another 5 cents.

Since the temperature maxes out so quickly I would say the coolant is not being circulated through the radiator. That could be because the water pump is shot, the thermostat is stock in a closed position or a piece of debris is blocking some passageway. When the car overheats you can carefully check to see if the radiator feels hot.

Let me give you some more info then (I'm a cheap bastard and don't want to give money away to a mechanic if I don't have to). Drove it today to my stop, usually I make it there without the temp maxing out but today there was alot of traffic so the gauge maxed out for about 2-3 minutes of driving. Got to my parking spot and I hear a "boiling, bubbling" sound coming from the engine area (hood is closed). I had to leave so I did not have time to open it up and see what was bubbling like that. Any ideas?

Originally Posted by edmorel

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Let me give you some more info then

(I'm a cheap bastard and don't want to give money away to a mechanic if I don't have to). Drove it today to my stop, usually I make it there without the temp maxing out but today there was alot of traffic so the gauge maxed out for about 2-3 minutes of driving. Got to my parking spot and I hear a "boiling, bubbling" sound coming from the engine area (hood is closed). I had to leave so I did not have time to open it up and see what was bubbling like that. Any ideas?

I am not a mechanic so take anything I take with a few grains of Fleur de Sel (Ile de Re sourced prefferably). The boiling bubling could be steam escaping from the radiator cap. The cooling system is designed to operate under pressure so if the rubber seal wears out on the radiator cap the system will not operate properly. If you plan to do the repairs yourself, you should check which cooling system components your car has and then methodically verify each one is working properly. A standard american car of mid 80's would have a fairly symple system. Mercedes may be different.

Originally Posted by edmorel

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I thought I'd ask here rather than go to the myriad of Benz forums.
Yes, but unfortunately the MB forums are where the answer lies.