How to purge air from OM603 coolant? 1987 300D
 

For the life of me, I cannot seem to get the air out of this thing. I recently did some work on the cooling system to try and bring my temps down a bit, but after the work the car is running even hotter!

I have a new thermostat, water pump, fan clutch, and expansion tank cap all installed. After I refilled the coolant, the temps will quickly get up to 100*C or even a bit more while driving with the heat/defroster turned all the way up.

I filled it with the front end raised, ran it with the defroster on for 30+ minutes, tried squeezing the upper hose with the return line clamped. Anybody have any other tricks or suggestions to try?

Remove thermostat and see if any difference.
Its either the stat or the water pump impellor isn't turning !!!.
These 603's self bleed quite easy ,you mentioned using defroster so heater has bled ok.

I know the thermostat is good for sure, I tested it before I put it in. The water pump is also brand new, and in good working order. The behavior is symptomatic of trapped air.

Not to be argumentative, but the general consensus is against you; these engines seem to hold air forever.

Is coolant coming back to expansion bottle , thin pipe from cylinder head /possble its gunked up at head connection and this would stop correct circulation.

Mine has always bled itself but my partners 98 w210 e300td would need the hose loosening off the duo valve to let air out and water into the heater matrix so maybe you could give that a go.

Did the thermostat have a toggle ? And if so was it fitted with it in the 12 oclock position ?.

I drained and refilled and managed to get it with no air trapped by going painfully slow. Like, pour a cup in the expansion tank, pour a cup through the upper radiator hose, wait 5-10 minutes, and do it again.

The thermostat only fits one direction. I'm not sure which way the valve is oriented, though.

Unfortunately, I'm still having flow problems (temps are back to about what they were before I did the work), so it looks like I need to replace my radiator after all. Darn, I was trying to avoid that.

I have a number of OM60x engines and I never have to bleed air from the radiator. I just drain the coolant and refill it from the expansion tank. I think you have other problems in the coolant system. How quickly the temp goes up to 100C with cold engine? How fast the upper hose is hardened?

with almost any 60x engine I backfill the engine from the upper radiator hose first - it takes about a gallon, then I fill from the expansion tank.

When you fill from the expansion tank only you will have to deal with filling the engine slowly by just a trickle going in from the top radiator hose. This can lead to overheating very quickly.

The small tubing and passage into head must be clear...

But the 603 self bleeds very well.

+1 60X engines are self bleeding, as long as the vent line is clear and the radiator isn't plugged.

small tubing and passage to the head
 

Where is the "small tubing and passage to the head"

Are you speaking of the line from the radiator to the recovery tank?

Thanks!

I believe he's talking about the line between the head (connects next to the upper hose) and the expansion tank.

I have had a problem with it running hot for as long as I've had the car. I was having trouble testing if I had it fixed after my new water pump because there was air trapped. Apparently my 603 doesn't bleed air as well as everybody else's, so I had to drain and refill very very slowly.

After getting all the air out I am still having the same problem. It feels like there's very little water flow when I squeeze the upper hose at any temperature. I'm in the process of replacing my radiator with a Nissen unit now.

For anyone curious, the current Nissens (build date 2015) seem to not have metal reinforced necks, and there is a plastic tab on each side at the top that needs to be trimmed off/bent for the radiator to fit. The Behr unit I pulled out doesn't seem to have either of those issues.

Try the backfill procedure, it makes the filling quite quick.

I did that, and actually do ever time. It seems like the main cause of my frustration has been a partially blocked radiator that wasn't allowing air to escape. With the new radiator in it seems to be self-bleeding a bit better, and running cooler. It is still running a bit hotter than I would like (still touched 100* going up a slight hill at ~30mph), but it also seems to be even cooler today than yesterday. I think in another day or two it might have actually bled all the air out properly.

Do you have a #14 head? The overheating and trapped air in the system are symptoms of a cracked head or failed head gasket. Normally the cooling system on these engines self bleeds very easily.