Water Pump or Something Else?

[dkr]

I have had a slow coolant leak and this morning ran a pressurization test. Upon pressurization, I have a leak coming out of just to the side of the hose connecting to the bottom of the thermostat bracket. It does not appear to be coming from any of the hoses, so it is dropping right on the alternator bracket. This is for a 1984 300D with 165K miles. I actually have a new OEM water pump in the trunk as I figured it would fail sooner. Is there anything else this could be?

Thanks,

Dkr.

[tangofox007]

From the pictures, I would put the thermostat bypass hose high on the list of probable suspects.

[Rogviler]

And maybe not even necessarily the hose, although it probably does need to be replaced. The housing ins and outs get corroded and pitted and they themselves leak. I've had some luck with repairing them with JB Weld, although I had two start leaking again after two years and I had to redo them.

-Rog

[ROLLGUY]

Originally Posted by Rogviler

And maybe not even necessarily the hose, although it probably does need to be replaced. The housing ins and outs get corroded and pitted and they themselves leak. I've had some luck with repairing them with JB Weld, although I had two start leaking again after two years and I had to redo them.

-Rog

This one gets my vote as well.....Rich

[Diesel911]

If it turns out to be that short fat Bypass Hose area that was the first thing I fixed when I got the Car.

Once the Hose was off I found there was deep corrosion in some areas on the Hose Nipple.
I scraped those out down to the bare metal (you need to get rid of all of that white corrosion) filled the grooves with JB Weld epoxy and then took making tape and taped over it so that when dried it would be close to the contour of the hose nipple.

When cured and tape removed I had to go back and fill in voids and re-tape it. Eventually I had to take a file and sand paper to contour it properly. That was back in 2007 and I have no issues since then.

Can do the same with a lot of cooling system pitted or corroded areas.

This is not a job for the fast setting JB Weld. Use the regular slow setting JB Weld one as it takes the heat better.
If you use another make of Epoxy be sure to read the lable to see if it can take the Heat.

[dkr]

A few months ago, I had a similar issue and ended up replacing the clamp on the thermostat bypass hose, so it does fit there is an issue here. The water pump appeared to stay dry. If I pull the hose, can I find a replacement at the local auto parts store? There isn't anything Mercedes-special, is there? I have a feeling once it comes off it won't go back on.

Dkr.

[tangofox007]

Originally Posted by dkr

If I pull the hose, can I find a replacement at the local auto parts store?

What you can likely do is find a radiator hose with a straight section with an approx. 42mm ID. It won't be as good as the genuine part, but it will work. You will also need a thermostat housing gasket.

Originally Posted by dkr

I have a feeling once it comes off it won't go back on.

If I was going to go to the trouble of removing the bypass hose, there is no way I would not replace it with new.

[Junkman]

I think they are available from this site. Or something like "mercedes 617 coolant bypass hose" in a search engine will bring up sources.

Here's the destructions from this site using those search terms. Part numbers are there also and will bring up sources.

DIY Water pump Bypass hose replacement, OM615, 616, 617

[BillGrissom]

I 4th comments above. I replaced w/ silicone hose on my two 300D's (42 mm I recall). You can buy on ebay, or anybody in Sacramento area can stop by and I'll cut-off a slice for you and sell cheap since I still have ~30" length left. Or you can buy original rubber on P-P, which might last another 20 yrs. You will need to remove the T-stat housing to do a decent job, and the aluminum will likely be a bit pitted. Both my 300D's now have Evans Coolant so no more corrosion worries.

While in there, you have good access to the timing chain tensioner spring which usually wears a flat on the side in a 300D and is cheap. Also, a good time to remove the T-stat to verify in a hot pot and also change the ear'ed O-ring (buy separate, a T-stat box usually has a common O-ring that doesn't fit).

[dkr]

Ok, so I somehow really messed this one up. I put in the new gasket, new bypass hose, and reconnected everything. When I turn the car on, the temperature just goes up and up until I turn the engine off at 100 deg C. When I feel the upper and lower radiator hoses, both are cold. Somehow coolant is not circulating. The thermostat is put in the right orientation. There are no apparent leaks. I added coolant until the overflow tank is at high and the coolant just sits there. I replaced the thermostat about a year ago and aside from a tiny leak have had no problems with temperature. Any ideas?

Thanks,

Dkr.

[tangofox007]

Originally Posted by dkr

Any ideas?

You probably have a slug of air in the head.

You might disconnect the upper radiator hose at the radiator end, then elevate it and see if you can add additional coolant via the hose.

[dkr]

I have a special funnel for bleeding air from the coolant system. In general, I fill there and keep coolant in the funnel and keep revving until the bubbles go away. Are you saying there was enough air in the head to block the whole system? When I checked, there were no bubbles at all...

Thanks,

Dkr.

[tangofox007]

Originally Posted by dkr

Are you saying there was enough air in the head to block the whole system?

The air doesn't "block" anything. It just doesn't conduct enough heat to the thermostat to cause it to actuate.

[dkr]

Thank you. That did fix it.

This was one of those jobs where everything seems to have gone wrong. My Gano coolant filter came apart in multiple pieces inside the upper radiator hose and the threads on one of the thermostat housing connections are messed up, but I'm happy to have a car to drive again.

Dkr.

[ROLLGUY]

I learned a long time ago that these cooling systems need to be filled from the upper radiator hose as well as the expansion tank. The thermostat is located on the engine inbound coolant path, rather than the outbound (like the old American made engines I was used to).