looking for a coolant leak on my 87 300d where do I look - PeachParts Mercedes-Benz Forum

777funk · #1 03-10-2009, 10:02 AM

I've got an 87 that has been holding coolant just fine until around 2 months ago or so. Now I'm having to refill the reservoir once every couple weeks at least. And I don't drive it usually more than maybe 60-120 miles a week.

But... I've looked around a little and it's so slow that I can't see a leak (or maybe it's somewhere I can't see).

Where do I look?

Also, I know I probably can't mention the year 87 here without someone saying cracked head

so I give some background... the low coolant reservoir light has started coming on just recently with NO overheats. The temperature has never gotten above normal (80-100 C). So I don't think we have a cracked head. But just for some background... there's that.

JonL · #2 03-10-2009, 10:55 AM

Yeah, well I'm going to say it even with the background info.... maybe a cracked head. I had a slow coolant leak just like yours with no overheating incidents for over a year... finally got too bad to drive. The head was cracked behind the cyl. 1 exhaust valve seat. The casting was simply too thin in that area. Hopefully your head is not cracked, but it might be.

Slow leaks like you have... I'd look carefully for signs of leakage at the lower weep hole on the water pump, and I'd suspect the heater core. Do you smell coolant in the cabin? Do you get a film on your windshield?

Jeremy5848 · #3 03-10-2009, 11:35 AM

Remove the belly pans (if you still have them) and always park in the same place. If there is a slow drip somewhere external, it will eventually show up on the floor/ground. If nothing ever shows up, it may be an internal leak, even as Jon notes.

777funk · #4 03-10-2009, 12:00 PM

Quote:

Originally Posted by JonL

Yeah, well I'm going to say it even with the background info.... maybe a cracked head. I had a slow coolant leak just like yours with no overheating incidents for over a year... finally got too bad to drive. The head was cracked behind the cyl. 1 exhaust valve seat. The casting was simply too thin in that area. Hopefully your head is not cracked, but it might be.

Slow leaks like you have... I'd look carefully for signs of leakage at the lower weep hole on the water pump, and I'd suspect the heater core. Do you smell coolant in the cabin? Do you get a film on your windshield?

I do have a film on the windshield. I'm not sure I smell coolant in the cabin...

but I do notice this, when I turn the heat on for the first time of the day I hear bubbling as the heater core fills up. I never used to hear this before the having to constantly top off the reservoir. I suppose that could mean that the heater core is draining slowly when the car is parked after running the heat. How would I find that?

on a side, I noticed that the reservoir cap isn't making a perfect seal (I can blow air into a hose connected to the upper side spill port hose).

JonL · #5 03-10-2009, 12:10 PM

The bubbling noise I think just indicates that you're low on coolant. It doesn't mean the coolant loss is through the heater core, although it might be.

You need a coolant system pressure tester. Fill the cooling system and pressurize it. Keep restoring the pressure as it leaks down, but don't overpressurize it. (Pressurize it to the same as your pressure cap rating... I don't remember what that is off hand, probably between 14 and 16 psi.) Look for leaks. If it is the heater core, you'll have to find the lower heat outlets in the cabin and look carefully for dripping. If you keep pressurizing it for a while, until you've lost maybe a half-pint or more of coolant, you should be able to find where it is going -- unless it is going into the engine. Good luck!

JonL · #6 03-10-2009, 12:13 PM

Oh, and the film on the windshield... Probably means that your heater core is slightly porous if not actually leaking. It can be porous enough to create that film without causing significant coolant loss, in other words much less loss than you are experiencing. But if you had no film at all I'd have placed the heater core lower on the list of suspects.

Pressure testing will tell the story.

777funk · #7 03-10-2009, 12:52 PM

My reservoir cap may not be holding pressure. I connected a hose to the spill port and I can blow into it. That may or may not be saying something. But I think it's original so maybe that's a good place to start.

JonL · #8 03-10-2009, 01:37 PM

Blowing into the spill port really won't tell you anything. The spill port is outside the pressurized portion of the system. Furthermore, a bad pressure cap is unlikely to cause you to lose coolant, especially during the winter. In fact an old trick when you have a leak someplace is to slack off the pressure cap so it cannot hold pressure... thus slowing down the leak. It's a good trick to remember if you ever get a pinhole in your radiator or in a hose, and you want to limp home.

LNGfish · #9 03-10-2009, 02:00 PM

On my 82 300SD I had a tiny drip leak on the Tubing that vents from the water pump to the head. It leaked in the back of the tubing so it was very hard to see as it dripped and it never reached the ground. If your car has this vent tubing, about 4 inches long and a U shape, you can run your finger around the upper top and in the back. This is where mine slowly leaked. I got a new one from Phil and it is fine now. I also replaced my Radiator cap and expansion tank and thermostat.

babymog · #10 03-10-2009, 05:51 PM

My '87 seemed to leak a bit, just if it was filled to the top of the reservoir. Not much, just that I couldn't keep it above the full line without adding a touch every month.

I sold it, and mentioned it to the new owner, and he told me that his other '87 leaked just a little, from the hose beneath the reservoir that leads out through the fender to the overflow tank hidden in the fender. He replaced the hose and all was fine. On my old one, it turned out to be a hairline crack on the pressure reservoir.

777funk · #11 03-16-2009, 10:22 PM

Found at least one for sure leak. It's at the base of the radiator where the plastic part (drain plug, lower hose port, etc) meets the metal. This is the passenger lower portion of the radiator. It looks to be above and the opposite side of the lower hose port which leads me to believe it's not the hose connection leaking.

So... am I looking at a new radiator? Get the old one fixed?

Any suggestions for the new radiator?

thanks,
Nick

sixto · #12 03-16-2009, 11:02 PM

FastLane doesn't list a radiator for your car but call Phil anyway.

According to gsxr, the only other radiator that fits is a radiator from a 500E/E500. This gives you a choice of having the reservoir line go to the top of the radiator or to the upper hose fitting on the head. The downside a flimsy plastic piece that can break ruining the radiator.

Sixto
87 300D