Pressure on the coolant system..... - Page 3 - PeachParts Mercedes-Benz Forum

Fulcrum525 · #31 08-25-2010, 09:20 AM

Quote:

Originally Posted by vstech

first thing in morning open hood. squeeze the upper hose, is it hard? if not, does fluid flow into the expansion tank? yes, good, no? air/not filled hose.
next.
start the car. let it idle for 1 minute. check the hose. is it HOT? is it Hard? no? good. shut down the car. pull the tank cap, look it over VERY WELL. how old is it? are there any cracks in the seal or the seat/spring pocket?
what pressure is the cap? yours should be a 140KPA I think... (about 22psi) perhaps you could drop it to a 120 or a 100, and see if it vents pressure better.

Just did these tests.

Upper hose had pressure on it (Hasn't been run in 16 hours)

I let the car idle for about 5 minutes before I could detect any heat in the upper hose. It had just gotten about the 40 line and it's around 60 outside. (Not sure what you meant by fluid flowing into the tank, by squeezing it or by removing the cap? Either way there is coolant in the expansion tank)

I have the cap in front of me, it's the 140 and my father got it I think about 4 or 5 years ago. I don't see any cracks in the rubber but i'm going to go to the dealer and see if they have a lower pressure cap (HOPEFULLY that will be the answer)

funola · #32 08-25-2010, 10:47 AM

Have you checked the cap's opening pressure? You can borrow the coolant system pressure tester from Autozone. You can also rig up a pressure gauge by tee-ing into the line at the expansion tank. A 0-15 psi fuel pressure gauge at Autozone for $10, you'll also need a length of 5/16 hose. You can also run the gauge into the inside and watch as you drive. I have to agree too early for a head gasket.

Fulcrum525 · #33 08-25-2010, 11:40 AM

Quote:

Originally Posted by funola

Have you checked the cap's opening pressure? You can borrow the coolant system pressure tester from Autozone. You can also rig up a pressure gauge by tee-ing into the line at the expansion tank. A 0-15 psi fuel pressure gauge at Autozone for $10, you'll also need a length of 5/16 hose. You can also run the gauge into the inside and watch as you drive. I have to agree too early for a head gasket.

I went for a drive this morning and the bad cap theory is starting to turn a few cogs in my head.....

I drove to my indy to pick up a part (That hadn't arrived yet

) {9 Miles backroads only}
Before I left there I popped the hood and noted that the hose was hard so I took the cap off and relieved the pressure.

Then I drove to Farmington {15 miles, some highway, max speed 65} I turned the engine off and let it sit for about 30 minutes....when I came back I popped the hood and checked the upper hose....it was soft. I took the cap off again (I had a 20 psi cap in the trunk that I wanted to try but it didn't fit)

Drove home again {11 miles, highway, max speed 75) This time on the highway the coolant light kicked on again for a minute or two. While writing this I have been letting the car sit again for another 30 minutes. Just checked the hose....it's starting to go soft again but I did notice that there is coolant around the bottom edge of the cap on top of the coolant tank so something came out.....

Another thing....assuming that it isn't a bad head/gasket but that there is still too much pressure....what could be the source? Apparantly air getting into the system would be the culprit so the question becomes how is the air getting in? I should mention that I do have one leaking injector and the front cover on my engine has been leaking oil since this happened and it was not sealed correctly.

OM603: Freak failure of timing cover. 1987 300D

Perhaps one of these two areas is letting too much air into an otherwise good system? (I probably have no idea what i'm talking about but if it helps to know I might as well post it)

funola · #34 08-25-2010, 11:54 AM

Quote:

Originally Posted by Fulcrum525

I went for a drive this morning and the bad cap theory is starting to turn a few cogs in my head.....

I drove to my indy to pick up a part (That hadn't arrived yet

) {9 Miles backroads only}
Before I left there I popped the hood and noted that the hose was hard so I took the cap off and relieved the pressure.

Then I drove to Farmington {15 miles, some highway, max speed 65} I turned the engine off and let it sit for about 30 minutes....when I came back I popped the hood and checked the upper hose....it was soft. I took the cap off again (I had a 20 psi cap in the trunk that I wanted to try but it didn't fit)

Drove home again {11 miles, highway, max speed 75) This time on the highway the coolant light kicked on again for a minute or two. While writing this I have been letting the car sit again for another 30 minutes. Just checked the hose....it's starting to go soft again but I did notice that there is coolant around the bottom edge of the cap on top of the coolant tank so something came out.....

Another thing....assuming that it isn't a bad head/gasket but that there is still too much pressure....what could be the source? Apparantly air getting into the system would be the culprit so the question becomes how is the air getting in? I should mention that I do have one leaking injector and the front cover on my engine has been leaking oil since this happened and it was not sealed correctly.

OM603: Freak failure of timing cover. 1987 300D

Perhaps one of these two areas is letting too much air into an otherwise good system? (I probably have no idea what i'm talking about but if it helps to know I might as well post it)

Does not sound like combustion gas is leaking into the coolant. It does sound like you have a questionable cap. I'd go to Autozone and borrow the coolant system pressure tester and test your caps right in the store, also test a replacement cap that they sell, and buy one that fits your expansion tank and give it a try. The leaky injector and timing cover should have no effect on coolant system pressure.

As to the coolant level light, when it goes on, and you pull over immediately to check, what is the level in the expansion tank? The float switch is a magnet on a swing arm that acts on a sealed reed relay. There's nothing to clean. If the expansion tank level is not low, I'd replace the float switch. Don't buy a Meyle, or other "OEM" garbage float switch if you want a good one. Get a Mercedes unit. I bought one from Autoha@@@s and it failed within a year.

Fulcrum525 · #35 08-25-2010, 12:11 PM

Quote:

Originally Posted by funola

Does not sound like combustion gas is leaking into the coolant. It does sound like you have a questionable cap. I'd go to Autozone and borrow the coolant system pressure tester and test your caps right in the store, also test a replacement cap that they sell, and buy one that fits your expansion tank and give it a try. The leaky injector and timing cover should have no effect on coolant system pressure.

As to the coolant level light, when it goes on, and you pull over immediately to check, what is the level in the expansion tank? The float switch is a magnet on a swing arm that acts on a sealed reed relay. There's nothing to clean. If the expansion tank level is not low, I'd replace the float switch. Don't buy a Meyle, or other "OEM" garbage float switch if you want a good one. Get a Mercedes unit. I bought one from Autoha@@@s and it failed within a year.

The light only comes on at highway speeds above 70 or so and even then only when i've accelerated. If I hold was steady speed though it will turn off. I pretty much always stick to OEM equipment (As I told a friend recently...Mercedes and aftermarket parts don't make good bedfellows) Interesting that you mentioned not cleaning the sensor....a few years ago the light came on and stayed on while the coolant was full...we pulled it, cleaned it and it was fine afterwards.....

Which brings up a question, how reputable are the caps that Autozone sells? The only thing I buy there are cleaning products (Meguiars)

babymog · #36 08-25-2010, 12:15 PM

I would run a non-OE such as Autozone cap as a temporary measure, but that's just me. Should meet the spec new, but I trust the OE cap to meet the spec for years.

Fulcrum525 · #37 08-25-2010, 12:21 PM

Quote:

Originally Posted by babymog

I would run a non-OE such as Autozone cap as a temporary measure, but that's just me. Should meet the spec new, but I trust the OE cap to meet the spec for years.

That is my thought as well. After I get the starter into the 280CE, right now i'm just waiting for the part. I'm going to head to the dealer and ask for a new cap. I'm going to give one of the lower pressure units a try first, probably the 120 to start off conservatively.

Also I just went out and checked the hose again, it's pretty soft now....which is really perplexing, one time it stays hard overnight and then the next day it softens up again within an hour?

(Please let this is all be cap related) But again if I saw coolant next to the cap then the pressure was relieved but there still shouldn't be coolant coming out....right?

funola · #38 08-25-2010, 12:26 PM

Your expansion tank coolant level maybe at the min mark, and when you accelerate, the sloshing cause the level to change momentarily and triggers the light. Maybe there is nothing wrong with the float switch? There really is nothing to clean other than the hinge that the arm swings on.

I am sure the Mercedes cap is a better made unit. But an aftermarket cap, as long as it fits properly, should work fine. It is not a very comples device! I do understand if you want to use a genuine Mercedes cap. My suggestion for the Autozone cap is as a diagnosis tool for the problems you are having. It certainly is a lot cheaper than a head gasket.

babymog · #39 08-25-2010, 12:34 PM

Does the 126 have an overflow tank in the fender like the 124? If so, the tank in the engine compartment is for expansion, if it exceeds the cap pressure it goes into the neck, down the hose, into the overflow tank in the fender. If that overflow hose is blocked for some reason, your cap will not vent properly.

funola · #40 08-25-2010, 12:34 PM

You can't expect the interface of the cap to the neck of the exp tank to be totally dry. If pressure is being vented via the cap, some wetness there is to be expected. Do you have a vent hose at the neck of the exp tank? Whatever coolant that is vented normally go through that hose.

I see you prefer trial and error by replacing parts rather than diagnose with test equipment?

Fulcrum525 · #41 08-25-2010, 12:48 PM

Quote:

Originally Posted by babymog

Does the 126 have an overflow tank in the fender like the 124? If so, the tank in the engine compartment is for expansion, if it exceeds the cap pressure it goes into the neck, down the hose, into the overflow tank in the fender. If that overflow hose is blocked for some reason, your cap will not vent properly.

One expansion tank is on the left side only. Which hose are you talking about in this case, there are two. (One in the back and one in the front that goes to the radiator) Note this is an old picture...the expansion tank to radiator hose that you see zip tied is hanging loose and occasionally will find it's way on top of the support which makes closing the hood difficult (Which I always notice and subsequently move the hose back where it belongs) If your clogged hose theory is correct then I should probably check this one first as it might have been pinched a few times.

Quote:

Originally Posted by funola

You can't expect the interface of the cap to the neck of the exp tank to be totally dry. If pressure is being vented via the cap, some wetness there is to be expected. Do you have a vent hose at the neck of the exp tank? Whatever coolant that is vented normally go through that hose.

I see you prefer trial and error by replacing parts rather than diagnose with test equipment?

Haha sometimes

at least I have several new ABS sensors

. I have some testing equipment but not everything.

funola · #42 08-25-2010, 12:58 PM

Quote:

Originally Posted by Fulcrum525

Haha sometimes

at least I have several new ABS sensors

. I have some testing equipment but not everything.

You don't have to own the test equipment. That's why I suggested Autozone. You take the 2 caps you have, screw it onto the tester, pump it up, look at the pressure gauge when it vents and that's the opening pressure. If it does not vent and pressure continue to build, the cap is crap. It takes a minute to test. If the cap is fine, I would clean the seat of the exp tank and check that the vent hose is clear. You can also put the vent hose into a soda bottle to see how much coolant is vented.

Fulcrum525 · #43 08-25-2010, 01:03 PM

Quote:

Originally Posted by funola

You don't have to own the test equipment. That's why I suggested Autozone. You take the 2 caps you have, screw it onto the tester, pump it up, look at the pressure gauge when it vents and that's the opening pressure. If it does not vent and pressure continue to build, the cap is crap. It takes a minute to test. If the cap is fine, I would clean the seat of the exp tank and check that the vent hose is clear. You can also put the vent hose into a soda bottle to see how much coolant is vented.

Sounds like it's worth a shot then. After I pick up the starter for this 280 i'll stop Autozone on the way back and find out whats what.

babymog · #44 08-25-2010, 02:28 PM

The back hose leading from the filler neck.

BodhiBenz1987 · #45 08-25-2010, 04:29 PM

Quote:

Originally Posted by Brian Carlton

There is no urgency to accomplish this task and some tests should be accomplished to confirm or deny it. Testing includes an oil analysis for potential glycol in the oil and also includes a test for combustion by-products in the coolant.

If either of these tests are positive, you then have a basis for pulling the head.

However, be prepared for the worst if you do pull the head. Many times the culprit is a cracked head and not a simple head gasket.

I was about to suggest an oil analysis ... not that expensive and easy way to tell if you're getting coolant in the oil.
If you can grab a cap from the dealer and pop it on, that seems like the easy first step to me.

Also: the second expansion tank babymog is talking about on the 124 is hidden behind the rear of the passenger side fender, i.e., behind the wheel well. I also do not know if the 126 has one. I'd check on EPC but it doesn't work on my work comp.
As for air getting into the system, I don't think a leaking crankcase or injector would allow air into the water jacket. Oil will get out, but unless it's a place where coolant is coming out, I don't think air would be going into the coolant. A thought: Maybe the engine was not properly burped after the radiator replacement? Could be (or have been) a maverick bubble in there. However, I would think the main symptom of that would be overheating or patchy temperatures.
Based on my somewhat limited experiences and my own previous freakouts, I'd agree with others that it's likely a cap or a venting problem. If there isn't oil in the coolant or coolant in the oil, and the car is maintaining correct temperatures all the time and running well, it doesn't make sense to pull off the head. I would start with the cap, check the vent hosery, check the extra tank that we're not sure exists on the 126 (

), and if you're still concerned, check the oil for coolant and coolant for oil.
Hope you get it sorted out ... I hate it when I have that constant sense of worry ...