83 240D lost coolant, dunno where
 

My 18 year old son has been driving this 240D for a few months and today he had a problem. It stalled out at a light and he couldn't re-start. He was oblivious to the fact that it had run out of coolant.

When I got there, the cops had called a tow truck, who charged me $210 to tow it 50 feet to a parking lot.

Anyway, I limped it 7 miles home after refilling the radiator and watching carefully for overheating. It made it fine, although I swear it was having trouble shifting- I didn't take it over 40. Later at home, I drove it again, and it seemed to shift fine, so I don't know.

But here is the real question: the temp gauge is not reading. It is all the way at the bottom. And when I run the heater, it wasn't getting as hot as I'd expect. So it seems like the water pump is not pumping water. But I replaced this a year ago. And, I do not see any coolant at the weep hole, and no signs of coolant leak anywhere underneath. I put in a as much water as I could before driving it home, and now it is down a bit, but I think it was just getting air out of the system.

So, I'm at a real loss as to how it lost all of its coolant. I'm not letting my son drive it until I figure this out.

Another tidbit- not likely to be related- I think there is a marginal injector. At idle, espcially in drive or reverse, it shakes violently. It is has gotten much worse in this regard in the 2 years that the car has been revived and put on the road again.

The cooling system in these cars needs to be filled through the top radiator hose. If you just put coolant or water in the radiator, the engine will have no coolant because the thermostat is on the inflow side. Filling it through the top hose gets coolant into the engine. The temp gauge will not register if no liquid is in the engine, and the heater will not work either. You can rent (and then return for refund) a pressure tester from most auto parts stores. Be sure the system is full of liquid, or you will have to pump it forever. The leak should be evident once the pressure is up.

When was the last time the valves were adjusted?

I did the valves when I first was getting the car running a couple years ago. Not that many miles on it since. I made my own offset wrenches.

Coolant can go one of three places:

1. On the ground
2. Out the tail pipe - bad head gasket
3. Into your transmission - bad radiator

Check your transmission dips tick. If it looks like a milkshake, your transmission will need immediate servicing.

This sounds like tight valves to me. It would not hurt to check the valve clearance.

Trans fluid looks fine, and level is good.
No signs of white smoke from tailpipe.

BUT- after looking at tech tips, I realized that this car has no radiator overflow tank at all! It must have been removed by the previous owner. I guess it must have gotten hot in its past and overflowed, but since there was no tank to catch it, it just all went on the ground. Then when excess would normally get sucked back in when the temp goes down, instead the system got lower and lower.

This is a 1983 240D. I assume that this car came with the overflow tank originally?

I have never seen an overflow tank (factory) on a W123. The turbo models have an expansion tank, but still no overflow tank. Both have the hose from the radiator/expansion tank neck going to the ground. If you can't find a leak, you probably have a bad cap. I suspect you will find a leak though......Rich

You can't find one because it never came with one.

The hose tiny hose from the top of the radiator just below the cap shoots straight down onto the ground. Most people zip tie in a Gatorade bottle since it is strong plastic to the side of the radiator to see how much coolant has come out of that hose.

The top tank of the radiator serves as the expansion tank. The best way to fill this type of system is to fill it to the very top, right to the filler cap ring. First time it runs, it will puke out the excess, and after that it will be at the right level. Unless there's an air bleed port at the top hose connector, there should be no reason to bleed. Just make sure the heater is on when you fill it.

While trying to fill the system the otehr day, I idled it for 15 minutes. I didn't ever see the cooling fan come on. The temp gauge did move slightly, but was always at the bottom. The heater was blowing hot air.

When I removed the top heater hose (engine off), coolant came out of the hose and the rad so I quickly put it back. I stuck a garden hose in the radiator on a slow trickle and let it run for many minutes, then capped it, ran it some more. I let it cool down and topped it off.

I don't know what else I can do to "burp" the system.

AND- what is an easy way to check that the elec fan and its relay are working?

The electric fan cycles with refrigerant temp when the A/C is on. If the A/C wasn't on, you shouldn't be seeing the electric fan coming on unless the engine is *VERY* hot (>100˚C)

Thanks for clearing that up!

Now, I just need to figure out why the temp is reading very low/not at all. Sensor bad or air in system? I just topped it off, and I'll idle it for a while and see what happens. It is a hot day, so maybe something will.

It's been a while since I've had an OM616 in my shop but I believe this sensor is what you are looking for.

Attachment 147735

With the ignition key in the "run" position, ground the wire to the engine block. This completes the circuit and the fan should come on.