1985 300SD coolant leak and engine power loss

[85Piece]

Hi all,
I am hoping someone here can give me some ideas on where to start:
I have a 1985 300SD with ~ 230k miles. The engine mounts recently went and until they were repaired the engine got a terrible shaking at idle (for about 3 days of operation), all of that is fixed now.

Here're the new problems, which I think may or may not be related to the previous shaking:

A.) there is now a coolant leak, pretty bad one, really, which I can't quite figure out where it is. My guess is either near the thermostat or near the pump. My questions:
1. what is the best way to find the leak?
2. Are there common spots that tend to leak?
3. Is any of the cooling system connected to the vacuum system?

B.) the engine is now pretty weak (it does get up to speed, but does so slooooowly) to be clear, the exhaust is clean, so I do not think this a head gasket issue, no link between coolant loss and engine power...I can see the coolant dribbling out the front).
1. Could this be a vacuum issue?
2. Could a hose have been jostled loose?
3. Should all of the vac lines hold a vacuum in both directions?
4. Could it be an ALDA problem?
5. Could it have anything to do with the shifter bushings?
6. Any ideas where I might start looking?

Any and all advice would be appreciated!
Best,
Jim

[tbomachines]

I would start at the radiator hoses. All of that shaking from a broken motor mount could have easily stressed the old dry rubber hoses to the point of a small leak. The outside of the bends in the hoses are usually the areas that are the weakest and split, sometimes it can be very hard to see.

[oldsinner111]

replace that little 2 inch hose if hoses not replaced.

[iceman104]

1985 300sd. Engine is very strong lots of power. But I have a coolant leak some where. I never see it drip on the ground and I don't see it any where under the hood. Also I see none in the oil and same with the coolant. I drive about 80 miles for work round trip. When I get home and it cools down the tank in about half empy when I leave with it on the full mark. (The temp gauge does not work now but I belive that is the temp sensor running a test on that today) but could anyone help me find this leak its driving me crazy.
thanks in advance.

[tangofox007]

The best way to find a leak is with a pressure tester. Many parts stores will lend you one. Where I live, Autozone has the best tester for a vehicle with a conventional radiator cap.

[toomany MBZ]

^ Agreed, with post #3 too.

[iceman104]

Too many mbz there is nothing leaking from that hose it looks brand new honestly. the only hose I have question about is the one coming out of fire wall that is rubber then hooks to a metal hose. And the compression test the only thing that will tell me is if I have a bad head gasket right ? Also I don't know if I forgot to add but when I take the cap off the tank I have no pressure. Any other suggestions please. idk where it could he.
Thanks again in advance.

[HuskyMan]

A professional grade coolant pressure tester can work wonders. Before you can fix anything, you must have an accurate diagnosis. Amazon.com has quite a few coolant pressure testers, one of the few that have a 'five star rating' is this one, not cheap but quality tools usually aren't:

UView 550000 Airlift Cooling System Leak Checker and Airlock Purge Tool Kit : Amazon.com : Automotive

Other than that, what is your time worth? Check out a local indy who has a good reputation and he will solve your problem in rapid fashion while you sit back sipping on a Star Bucks reading the latest auto magazine sitting in the indie's waiting room. Life is good.......

[toomany MBZ]

Here are few shots of the firewall area, Can you tell which line is leaking?

Mono valve (right side ), or other heater lines (left side).

Pics of a 123.

[toomany MBZ]

Pics of a 126.

[iceman104]

The one on the passenger side of the car the rubber hose comes out the the second fire wall (the small fire wall) that rubber hose connects to a metal one it looks a little kinked but I don't fill anything wet or see any evadince of it being wet. I live 20 min from a good Benz man. river city imports Jeffersonville IN. He is just always so busy great guy and very honest (this is my 3rd 300d/300sd) I just was wondering if I could
Find this issue my self.

[bolzano]

Made my own pressure tester for the leaky 300SD and found the leak. Would never have found it otherwise.
Had small leak, a few ounces a month. No overheat. Changed all coolant hoses. All heater hoses. Still leaked.
Made pressure tester. Made it from small hose, bike tire valve from leaky tire tube, bike tire pump.

Remove hose from coolant reservoir as in picture. Plug it and clamp to make air tight.
Get another small hose which will fit on same fitting on coolant reservoir. Cut off a bike tire valve. Mine is cheap. Happened to be same size as car tire valve. Reshape bike tire valve to a tube like device that will fit inside the hose and so you can clamp it to be airtight.

Put your hose + tire valve on coolant res. Pump up and do not exceed 15 psi. Estimate by pumping you bike tire and measuring PSI. You do not need 15 psi most of the time to find you leak. Less may do.

Found my leak. Was in windshield heater element near right windshield wiper. Had to remove stuff around the wipers to see the leak. Bypassed leaky element with small hose. No leak since.

This scheme will likely not work on other cars as MB coolant res is pressurized and most others not.

[Junkman]

Advance has a really nice pressure tester they loan out. Don't lose it, $200 retail if you do. I found several leaks all at hose clamps. I now pressure test anytime I replace a hose.

[iceman104]

I never was able to find the hose that is by the windshield fluid? Also if I do the pressue test its just going to let it leak without the car running right? That way I can look for it?

[bolzano]

Originally Posted by iceman104

I never was able to find the hose that is by the windshield fluid? Also if I do the pressue test its just going to let it leak without the car running right? That way I can look for it?

My 300SD has windshield heat. Had to remove wipers, black screen around wipers and maybe some other things to see windshield heat hoses. Be careful to use a puller to pull the wipers. Do not pry on windshield. Otherwise, crack windshield.
If your cyl head to heater hose on the driver' side near oil filter has this little branch, you probably have windshield heat. If not, no.
By the way, had a üroparts version of this hose that leaked when new.

Yes, the pressure tester should make the leak visible without running the engine.

If leak is near thermostat waterpump, then it would not be windshield heat leak. You can still pressure test and see where it leaks on the ground. Hope it is not a freeze plug.