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Old 07-25-2006, 04:46 PM
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Join Date: Jul 2006
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Thumbs up 190e 2.6 Overheating (1992)

I have purchased a 1992 190e 2.6 at Auction. The car looks great, virtually brand new. A the time of purhcase there were two obvious issues in the engine compartment.

A short section of the Radiator intake was broken off, where the hose connects to the Radiator. And the Heater Core was bypassed with a hose draped over the engine and back into the block (where the heater Core Return would normally go.

Problem - It Overheats

Due to it's age and questionable up keep, I am replacing more than simply things I know are broken. I have replaced the following in search for a solution to this problem.
  • Radiator
  • Thermostat,
  • Water Pump (What a Joy!)
  • Fan Clutch; Updated Version
  • Radiator Cap
  • Temperature Sender Switch; For Temperature Gauge
  • Radiator/Auxiliary Fan Switch; Blue Insulator with 2 Prong Connector; 130 Degree C
  • Coolant Temperature Switch; Black with Round Top and 4 Pin Connector; For CIS and Cooling Fan Control
Still have the same problem. On Idle the temp slowly climbs to 100, Aux fans go on, slowly continues to clime to 120.

Note: I have not installed the Coolant Temp Switch yet. (I have not found a tool to extract it yet) I did not think that it was the problem, only replaced because it was related to cooling and I was replacing all parts related to this topic)

Could it be that I am not "Bleeding" coolant into the system correctly and have an Air blockage?

Second Question. Is there any way to test the Heater Core while in Car. I can only assume that it is faulty and they previous owner could or would not replace it. Can it be pressure tested?

Last edited by SonicBlue1966; 07-25-2006 at 09:06 PM.
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Old 07-25-2006, 11:10 PM
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I don't know the timeline on any of this. If it was just recently done, you need to check the coolant level after the engine has cooled off. Other than that, unsure what the problem is, seems like you covered all the bases and then some. Maybe a plugged condenser? Oh, is the fan installed correctly? It can be reversed (talking about the one on the pulley, not the electric aux fans).
On the heater core, if it's now getting coolant and no leak, good sign. It may be that the heater valve (mono water valve) has a tear in the diaphragm and it is heating the heater core, which is why it was bypassed. The diaphragm is available seperately and is easy to replace, it's over near the battery.
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Old 07-25-2006, 11:17 PM
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head gasket next, my 1985 190e 2.3 8v had a bad head gasket causing temp problems.
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Old 07-25-2006, 11:20 PM
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Yeah the 2.3's were known for this, the 2.6 not so. The 2.3's problem usually started with a plugged pair of pre-cats, actually there was something more basic that contributed to the plugged pre-cats, can't remember what that was right now though, but yeah you had this slippery slope which all kind of ganged up and wrecked the engine sometimes on the 2.3's, pretty bad deal.
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Old 07-25-2006, 11:36 PM
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Overheating for about one year had haunted me, it was solved by replacing the Radiator, the Fan Clutch and Fan Clutch Bearing Bracket.

The bearing bracket is very important because if the bearings inside are shot, the belt will spin the fan clutch pulley but the fan will not spin at the proper speed. Happened to me, and I would not have known it until I saw the engine running but the fan was not spinning.

Also something that has not been mentioned here is that you may have improperly filled coolant back into the system. This was one of my newbie mistakes. Make sure one of the bolts on the engine block (right below/beside the oil cap) is undone to allow for air to escape. Engine will also making a knocking noise if there is air in the cooling system at higher temperatures.

Other than that, you have covered the most important parts of the cooling system.

190e 2.6 1990. 300,000 KM
C230 K 2000, 130,000 KM
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Old 07-26-2006, 10:53 AM
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Check the temp sender unit for the temp guage. Make sure its not maxing out or zeroing out and giving you false readings.

Check your aux water pump

Check that you have purged all air out of the system by leaving the cap off and rev ing the engine.

Check the radiator cap.

Then freak out about the headgaskette.
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Old 07-27-2006, 02:25 PM
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My Take

As previously mentioned, I too hope its not the head gasket or any type of breach bet the cooling and engine.

Simple causes of overheating are usually bad stat and/or water pump.

With this aside, see if the water is in fact circulating once you get up to temp. I normally do this with the rad cap off while engine is cold and run it to temp. Don't have a 190 so don't know if it has rad cap or just a reservoir. Either way. (since you replaced water pump, there should be no question that it is circulating).

If you are getting heat from the heater, heater core should be ok.

Back to the breach thingy. I had a Ford Taurus that lost coolant all the time - no drips, no signs of where it was going. Averaging 1 gallon a week. this went on for 3 years. The car would overheat only on long distance trips (probably cuz the coolant gets depleated). The car ran fine until recently it started chugging, oil looked milky, milky condensation on oil fill cap.

Had the engine replaced ($1300) with 10k engine. old one had 170k. No more coolant loss.
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Old 07-27-2006, 07:00 PM
david s poole
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are you sure that the thermostat is in the car because your symptoms sound just the same as no thermostat[in these pumps the coolant will by pass without stat in place] just a thought. david poole.
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Old 07-27-2006, 07:05 PM
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Even without the bypass, a missing/removed thermostat can and will create an eventual overheat because the coolant is not allowed to stay in the radiator long enough to shed the proper amount of heat, so yes make sure there is a thermostat. Unless it overheats in 5-10 minutes, it takes longer to overheat without a thermostat as opposed to say a plugged radiator or a stuck closed thermostat, but it WILL eventually overheat.
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Old 07-31-2006, 03:21 PM
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The Solution

Well, after checking and re-checking everything was convinced that I had a air pocket problem.

Originally I filled the radiator with the front bolt on top of the head off until I saw coolant flowing out and then closed.

Started the car and it slowly overheated. Left the radiator cap and saw bubble occasionally come up.

Let cool overnight and noticed that the overflow had gone down. Added more coolant. Same result.

I then let it warm up to 120, and carefully backed off the front bolt on the top of the head. It pissed like steam. I let it finish pissing and cool, put a funnel in it and filled with coolant from here.

Now everything is fine and it does not get much above 80. Now why should I have had to do this to make sure the entire system had coolant? Nothing I have read states that you need to add coolant directly into the Head?

Anyway thanks much for all of your advice.

It was a real sanity check. Working on this Mercedes has really shakin my confidence. Over the weekend my 95 Jeep Cherokee had a Alternator go out. I had it replaced and functioning in less than 1 hour. Guess I will work on this to bust my self image every now and then. I really like these Mercedes cars, just wish the 2.6 190 was easier to work on. My hands don't fit anywhere in the engine compartment and nothing seems to be easily replaceable!
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Old 07-31-2006, 05:44 PM
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When you filled it the first time did you have the heat in the car on full heat and fan? You are supposed to fill the resevoir, then run engine to temp keeping an eye on the coolant in the resevoir. All the while your heat should be on full hot and full fan. Next you burb the system via the upper rad hose. Squeeze the hose and hold it then clamp off the little tube going to the resvoir from the thermostat housing and release the hose. This forces air out and sucks coolant in. This takes a while.
2003 Pewter C230K SC C1, C4, C5, C7, heated seats, CD Changer, and 6 Speed. ContiExtremes on the C7's.

1986 190E 2.3 Black, Auto, Mods to come soon.....
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Old 07-31-2006, 08:47 PM
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I hear alot of these "bell and whistle" types of explainations to fill the cooling system. It's really quite easy, only requires a short roadtest and 5 or 10 minutes of your time. Fill it as much as possible, engine cold. Roadtest with heater if DEF. Keep an eye on the temp gauge. You will want to drive it a little on the hard side, harder accelerations. Not to the floor, just harder than most people would drive. You only want to drive about a mile. Try to end up at home or your garage. You want the temp up to around operating temp, it'll go there failry quickly. If you have to drive more than a mile, take coolant with. The indication that the system is not yet burped is a cold running DEF vent. Once you have it right around normal op temp, shut it off and leave it alone (cap is on the whole time). WAIT for the thing to burp, will only take 5 minute to 10 minutes, WAIT. Once it does you'll normally get 1/2 gallon to a gallon in it. Road test again, following same procedure. IF THE TEMP GAUGE PEGS, SHUT IT DOWN. Wait for a burp. Even on the first road test. Don't let it get much over normal. That's why it's best to take a jug of coolant along, just in case. You can stop and wait for the burp and bring it back home without worrying about blowing the headgasket, which is what you are always flirting with when filling a drained cooling system. It isn't rocket science, you should never have to open anything but the cap.
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Old 07-31-2006, 10:55 PM
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Location: Northern Calif. (Fairfield Area)
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I really like Dr. House. You at least stated the year make and model, but you failed to state where in the world you are. Believe me it can be an important piece of information for a proper diagnosis. Without that info and with the info you provided, I think you have a restricted radiator. I know. You just replaced it. Take it for a drive and check the whole back of the radiator with your hand for cool spots with the engine off of course. You didn't say the car rons hot at highway speeds or climbing which could be symptoms of a headgasket problem.

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