1979 300D coolant leak. - PeachParts Mercedes-Benz Forum

alfa 75 · #1 12-13-2007, 04:21 PM

I think my 300D is playing tricks on me.

Yesterday I went out to start it. It was rather cold (30 or so) and I hadn't plugged it in so I didn't think it would start but gave it a shot anyways. I cranked it for a while and sure enough, it wouldn't start. Not a big deal, I took a different car.

When I got home about three hours later, I noticed a small puddle of coolant under it that wasn't there before. It did NOT have a coolant leak until then. I couldn't find where it was coming from, just that it's coming from the front of the engine and eventually drips down the oil pan.

I went out to it this morning and it hadn't leaked any more, it still had plenty of coolant so I took it to go take a final exam at school, roughly 3 miles away. During the trip it fully warmed up (didn't overheat), same with the trip back. However, I didn't notice ANY coolant at all at school and I just checked, no coolant under it now.

I can't find where it's coming from. The upper radiator hose has a small seep but I don't think that's it. My other guess is the water pump but it's not leaking from the weep hole. The area below it looks wet but it doesn't feel wet where it bolts to the block. It's old as hell though so it could be the case. There's no coolant in the oil or vice versa, I don't think it's a headgasket issue.

Any ideas as to what's leaking here? I can provide a picture if that helps.

Newguy · #2 12-13-2007, 04:39 PM

Mine too was seeping, only from the thermostat hose. It would leek a significant more amount while the block heater was plugged in.
I found a loose hose clamp to be the culprit.

Maybe the warmth of the coolant and hoses has to do with the disappearing act of the leak.

Good luck.

alfa 75 · #3 12-13-2007, 05:46 PM

I'll look into it, thanks.

alfa 75 · #4 12-13-2007, 09:52 PM

Any other ideas about this?

kerry · #5 12-13-2007, 09:58 PM

Leaks like that are usually water pump leaks in my experience.

JimmyL · #6 12-13-2007, 10:07 PM

Quote:

Originally Posted by kerry

Leaks like that are usually water pump leaks in my experience.

Yep. Either that or since you have no overflow tank it can puke out the little hose off the radiator neck.

alfa 75 · #7 12-14-2007, 02:13 AM

Quote:

Originally Posted by JimmyL

Yep. Either that or since you have no overflow tank it can puke out the little hose off the radiator neck.

Not the hose, thank you though. So water pump it is, I guess. Strange that it seems to go away sometimes..

raslaje · #8 12-14-2007, 02:59 AM

Quote:

Originally Posted by alfa 75

I think my 300D is playing tricks on me.

When I got home about three hours later, I noticed a small puddle of coolant under it that wasn't there before. It did NOT have a coolant leak until then. I couldn't find where it was coming from, just that it's coming from the front of the engine and eventually drips down the oil pan.

I had the same problem on my 85. Turned out it was the short hose (approx 3 inch long) connecting the thermostat housing to the water pump. The ends had become spongy and no mater how much I tightened the clamps the antifreeze would just permeate out the end.

Biodiesel300TD · #9 12-14-2007, 10:50 AM

Use an air compressor and pressurize the system with a few PSI. If you don't have an overflow bottle you can pull the overflow tube off and use that port to pressurize the system While someone is sealing the system, look around for active drips. It sounds like the water pump is the culprit. But this will tell you for sure.

alfa 75 · #10 12-14-2007, 02:25 PM

Update! I've found the leak, I think. Seems to be coming from the metal pipe that goes from the thermostat unit to the water pump (see photo).

What exactly is leaking here? I was under the I guess false impression that only the water pump impeller leaks on these. Is it the actual water pump?

This is kind of urgent for me because I'm moving out of the country soon and was sadly planning on listing the car for sale on Monday (can't keep it, as much as it utterly breaks my heart to sell it.) I can't really do that until I fix this.

Thanks for the help.

tangofox007 · #11 12-14-2007, 07:01 PM

Quote:

Originally Posted by alfa 75

So water pump it is, I guess. Strange that it seems to go away sometimes..

An intermittent leak is very typical in the case of a failing water pump shaft seal. Often it will not leak when the engine is running, but will leak after shut down while there is residual pressure in the cooling system.

alfa 75 · #12 12-14-2007, 09:58 PM

So am I better off replacing the pump and the seal at the same time?

alfa 75 · #13 12-15-2007, 01:31 PM

Anybody?

kerry · #14 12-15-2007, 03:40 PM

I can't interpret your pictures well enough to help. But if you're asking should you replace both the water pump and the shaft seal together, the answer is yes. You can't just replace the seal, practically speaking since you'd have to disassemble the pump and rebuild it in the process. Just easiest to replace the pump.
If you're referrring to another seal, sorry I can't figure out which one.

alfa 75 · #15 12-17-2007, 10:09 PM

Alright, thanks. I got a pump for it from the local Benz repair shop, installing it tomorrow.. hope that does the trick. Any advice?

Edit- found some great threads on water pump replacement.. thank you search feature.