Water pump or...? 1981 240D - PeachParts Mercedes-Benz Forum

hempev · #1 12-08-2010, 12:58 AM

So my 1981 240D had on occasion pushed the temp needle to the 120 mark, but would drop down in a few minutes with no other changes (is this what cavitation can cause?) Yesterday, however, something really busted: I was driving on the freeway (only doing 55-60) when suddenly a cloud of steam/smoke came out of my vents and from under the hood. Once I got it cleared out with the window down, I saw the temp gauge was in the red. I got off at a service station, and the radiator was spewing steam from under the cap - as it sat for a while, there was a click and the steam stopped (I think the cap has a 15psi threshold). Getting the cap off renewed the steam bath. After a while, I filled with water (getting a boiling reaction in the radiator at first!), and looked for visible leakage - there was none. I tried to limp home, but in a few miles, steam was coming from under the hood (no more steaming in the cabin, and cranking the heat to max gave me no hot air), so I got off again. Same thing as before - steam from the cap and then a click. I left it overnight and got it home the last few miles with care but no new incident.

I figure the water pump went out, but also wondered why the steam got into the vents - could a dead water pump do something to "blow" the heater core so water/steam leaked through? I have changed out a water pump long ago, but I may be back here asking for help if I get hung up. Let me know if anyone thinks I am looking for the wrong problem. Thanks.

toomany MBZ · #2 12-08-2010, 10:44 AM

I would think an inside steam issue would be a heater core problem. But make sure you weren't just getting some through the vents. Once you get the overheating issue sorted out, check for steam again.

Usually, water pumps leak from the weep hole, as a warning sign it's about to fail.

Your cap should be a 1.2 or 1.4 bar, (17.4 and 20.3 psi, respectively), so you have a "weak" cap if it's 15 psi.

Make sure you have the correct amount of water and a proper pressure cap, see what happens.

barry123400 · #3 12-08-2010, 11:26 AM

Check thermostat condition before going on to the waterpump I would think. That means changing it out with your past intermittent situation. Make sure the belt that drives the waterpump is not too loose as well but unlikely to be that.

Also if you did not eject all the coolant out of the old rugged type engine no damage is likely from the current episode. I own a couple of 240ds. How did you get out on the highway with one? My examples automaticallty deploy their brakes before on ramps.

Actually I have a special place in my heart for these. They will never build a simular vehicle to these ever again. Exception being tractors possibly. If you are a younger guy and like the car. Plus it is in reasonable condition.

Seek out the elusive five speed transmission that fits it. I almost despair of finding one but still keep my eyes open. Another good stratagy is to check the fuel pressure in the base of the injection pump. This to me at least has become very important over time.

I suspect the 616 engines especially wear their first cylinder rod bearings out with substandard fuel pressure over a long period of time. Plus it impacts many other things. You want to see at least 14 pounds pressure in the base of the injection pump. Nineteen pounds pressure is even better but the supplied lift pump on the 616 may not enable this.

To motivate you further as I am a slow thinker and never posted this before. The right fuel pressure sustained in the base of the injection pump at speed also makes the engine sound quieter or different I believe.

Not that a person would like that with a 240d. I really do not know why I did not think of this benifit before today. Some owners of the 617 or five cylinder engines had reported the difference after correcting the fuel pressure earlier. So it would also apply to the four cylinder as well. Simplified an engine with better power balance at speed should be smoother and quieter.

vstech · #4 12-08-2010, 11:57 AM

... 5 speed is nice... I'm not sure which of mine I like better... 5speed 240 or 4 speed 300... I'll decide later

I certainly think the thermostat to be the likeliest candidate. sounds stuck closed to me.
get a new one in there!

hempev · #5 12-09-2010, 01:46 AM

I'm going to look into everything I can! Didn't know they had a 5-speed - with a 4-speed, mine is no speed demon, and I can't imagine what it would be like as an automatic!

barry123400 · #6 12-09-2010, 10:39 AM

Quote:

Originally Posted by hempev

I'm going to look into everything I can! Didn't know they had a 5-speed - with a 4-speed, mine is no speed demon, and I can't imagine what it would be like as an automatic!

Five speed is basically all gears 1-4 the same ratios as you have now. . The fifth gear is a straight overdrive to drop revoltions on the highway. Perhaps a little better fuel milage as well.

Dropping the noise level and rpms at speed is the appeal for me. If perhaps you stumble across more than one five speed or do not use the one you aquire. Drop me a private message.

Since some driving on these in my experience is done with the pedal to the metal every effort should be made to optimise the running and power. It is not as important on the five cylinders versions.

Since you seem interested another quick cheap check I always do is to examine the position of the injection pump arm with someone pushing the fuel pedal fully. You want to observe that is making the injection pump lever hit it's stop. There are far too many of these with this issue that is so easy to correct.

Different years wil have different linkages. On 1983 240d versions and some other years perhaps there are two rubber bushings that deteriorate and fall off for example that apply a rotary type motion to the linkage. It appears mercedes where not happy with the linkages as they modified them over time.

hempev · #7 12-09-2010, 07:40 PM

If how it is running is a sign of engine and injector health, my car is remarkably smooth - at any road speed, it is actually smoother and maybe even quieter than either of my 4-cylinder gas cars, and *had* been doing great for an engine with 470K miles on it.

The t-stat may be the original, since it is labeled "W. Germany".

I think the heater core is intact: no leakage anywhere, and this while forcing water in the system. Also, a finger spin of the water pump pulley displaces some water, so I'm not touching that yet. The local auto parts place was going to have to order the t-stat, so I just ordered one online with gasket and o-ring. Nothing to do now but wait for the FedEx man - not being the mechanic that a lot of you are, I don't intend to do more than is needed...I even regret that I took off the drive belt, since it can stay on with a t-stat replacement!

As for the transmission, I replaced all 3 rubber bushings from the floor shifter to the linkage because they were *not there*! The $5 part price was nothing compared to how hard it was for me to get everything lined up and re-installed. I did buy the bushings for the arms on the tranny itself, but those were still sound. I like how easy it is to shift through the gears, so I doubt I would be in the market for a 5-speed -- overdrive doesn't seem very necessary at the ~60mph I usually drive (I have gone faster at times, but it drops the mileage proportionally).

layback40 · #8 12-09-2010, 07:47 PM

Put your old thermostat in a can of water on the stove & heat it up. You will soon see if its any good. If you have a thermometer, you can check the opening temp as well. If it doesnt open up nice & wide, toss it.

hempev · #9 12-09-2010, 07:49 PM

Quote:

Originally Posted by layback40

Put your old thermostat in a can of water on the stove & heat it up. You will soon see if its any good. If you have a thermometer, you can check the opening temp as well. If it doesnt open up nice & wide, toss it.

Seems like a simple test - Thanks!

barry123400 · #10 12-09-2010, 08:21 PM

Not absolutly conclusive in your case if it it works in the water on the stove test. It was intermittent or appeared to be earlier. But on the other hand if it stays closed you absolutly have your issue.

My feeling is it was somehow jamming or sticking closed on occasion. Rather than a constant defect as most of the time the cars operating temperature was normal.

I live in an area that one can keep the speed down to 60 mph or 100km per hour if you like. Less on secondary highways. The highways between major towns here are four lanes usually with a separation barrier of a grassy strip. Or at least in the areas I frequent.

There is very little traffic usually. The density does rise a little during vacation season. This is easily understandable as there are less than two million people spread across the four maritime provinces. The major highways are just overkill for the volume of traffic but are a north american standard type of thing. You are right a 240 is much happier at 55-60 mph. Actually when they were produced the highway speed was 55 miles per hour.

hempev · #11 12-09-2010, 08:23 PM

I did some heat testing with my old thermostat:

First, let it sit in 195 degree water from my hot water dispenser --> nothing
Second, put it on the stove with the flame on high --> once it got hot, it started to open. Took it off (with tongs) and held under cold tap water and it closed.
Third, bring it to a boil in a pot --> by about 185 degrees, it started to open.

Soooo, either it was working and was touchy or it wasn't and extremes of heat made it work. Either way, it will be replaced and the next test will be with the engine reassembled.

barry123400 · #12 12-09-2010, 08:28 PM

Should have opened in the 195 degree water test as well. So it looks like the thermostat if your thermometer was accurate.

There is also a change it was picking up more heat than the thermometer was reading from the bottom of the pot or pan when accelerating to a boil. So in fact it may have been going higher than the 185 indicated. A slower heat conductive item between the pan and thermostat might have indicated otherwise.

layback40 · #13 12-09-2010, 08:32 PM

That thermostat is probably bad. Should have opened in the 195 deg water. Depending on the set temp, should be stamped on it, I would have expected it to be open at about 175deg F.

t walgamuth · #14 12-09-2010, 08:38 PM

I would have stopped driving it when I got steam out the vents. I hope you lucked out and have not done major damage to your motor.

junqueyardjim · #15 12-10-2010, 11:37 AM

What was the out door temperature where and when you were driving. At 20 degrees F with a watered down batch of what one thinks is antifreeze, you can get a radiator to freeze up pretty quick on the highway. Sounds like a freeze-up to me. I would say you better check your antifreeze.