New expanssion tank craked and leaking coolant. Overpressure? - PeachParts Mercedes-Benz Forum

juribe2 · #1 08-13-2007, 07:23 PM

Hi,

I need you advice again. About 6 months ago I installed a new expansion tank, new pressure cap, new hoses and new thermostat on my M104 engine. I also installed a new radiator about 1 month ago.

Now, the new expansion tank is cracked and leaking coolant thru those cracks. There is a long longitudinal crack and 4 spot cracks.

Do you think I got a defective tank or do I have some overpressure in the system (pressure cap is also new and identical to the old one). I also notice that the upper radiator hose increases diameter when the engine is hot (a little inflated).

Do I need to get a new tank and cap or is is something different?

BTW, parts for this car are getting hard to get. This tank is not available online and the intake air temprature sensor is also out of stock in every online store.

Thanks !

RAYMOND485 · #2 08-13-2007, 08:03 PM

1984 300d Turbo
The Head Seal Is Leaking Cyl Pressure To The Water In The Head
Install New Head Seal

juribe2 · #3 08-14-2007, 09:21 AM

Quote:

Originally Posted by RAYMOND485

1984 300d Turbo
The Head Seal Is Leaking Cyl Pressure To The Water In The Head
Install New Head Seal

Thank you for your reply. Are there any other possible symptoms to a head gasket failure? Oil and coolant are not mixed and I think coolant is not being burned because coolant loose is too small (just the small leak thru tank leaks). That gasket was replaced a year ago.

Could a bad pressure cap be the source of over pressure? The original cap was a Behr and the new one is labeled as "German" and has some differences inside but is rated for the same pressure. I reinstalled the behr cap last night.

wscheffer · #4 08-14-2007, 09:46 AM

The over flow would disburst the pressure along with coolent. The expansion tank should not contain enough pressure to crack it if the over flow is working correctly!

juribe2 · #5 08-14-2007, 10:21 AM

Quote:

Originally Posted by wscheffer

The over flow would disburst the pressure along with coolent. The expansion tank should not contain enough pressure to crack it if the over flow is working correctly!

I second that. That's why I think the pressure cap is bad (new but bad) because it is rated for 1.4 bar (20 psi). At that pressure it should open and relive the presure thru the over flow hose. Is that correct?

G-Benz · #6 08-14-2007, 10:27 AM

The cap should relieve pressure through the overflow hose, yes.

I have once had a coolant expansion tank crack...and it wasn't related to excess coolant pressure, as the system operated properly...just a bad tank, I guess.

wscheffer · #7 08-14-2007, 10:30 AM

Yes, the cap should have opened to relieve the pressure.

Instead of buying a new expansion tank maybe you can use a good sealant to stop leakage since the pressure it is under is relatively low. At least till you rectify the problem.

If it was the head their should be mayo under the oil cap or oil in the coolant or some other sign of it leaking.

Hope This Helps!

juribe2 · #8 08-14-2007, 10:41 AM

Quote:

Originally Posted by wscheffer

Yes, the cap should have opened to relieve the pressure.

Instead of buying a new expansion tank maybe you can use a good sealant to stop leakage since the pressure it is under is relatively low. At least till you rectify the problem.

If it was the head their should be mayo under the oil cap or oil in the coolant or some other sign of it leaking.

Hope This Helps!

There is no mayo in the system. What kind of sealant could I use? Some epoxy glue or something?

wscheffer · #9 08-14-2007, 10:51 AM

Not too sure exactly which one, but if you go to the auto parts store and ask a knowledgeable attendant.

You know one that know what their talking about which is a quest with in itself.

I am sure that with the wide variety of products produced by permatex, dow, elmers just to mention a few I am sure that you will find one that will suit your needs.

Hope This Helps!

nhdoc · #10 08-14-2007, 11:25 AM

MB OE Parts are guaranteed for a year. I'd talk to the dealer you ordered them from and tell them the cap must have been faulty or the tank was defective...either way they should replace them for free if it has only been 6 months. I agree that if you had a headgasket leak the pressure would disappate if the cap was working correctly.

juribe2 · #11 08-22-2007, 03:40 PM

Hi,

I already ordered a new tank. But, since it takes about a week to get it delivered to my country, I decided to try sealing the cracked tank using a strong hobby epoxy glue. I removed the tank, cleaned the surface and carfully sanded the cracked area before applying glue. I let it dry for 24 hrs. After driving the car for a couple of hours today, I discovered the cracks are back and looks like the tank is about to start leaking bad. I also notice the upper radiator hose is "inflated" when the engine is hot. Both tank and hose are 6 months old. The car is NOT overheating and I have tried with 2 different pressure caps (one MB original and the other one "Germany" branded, both rated to 1.4 bar).

Things I haved replaced in the cooling system during the last year: water pump, all hoses, thermostat, radiator, expansion tank, expansion tank cap, coolant. Fan clutch and aux fans are working normally. Car temperature is also normal.

I'd like to belive it is just a bad tank.....

Any aditional comments will be greatly appreciated.

P.S. Thank God Boing engines are made by Rolls Royce....

Thanks.

juribe2 · #12 08-25-2007, 06:22 PM

New tank arrived today. I'm going to replace it tonight and hope this solves the problem.

sdpartz · #13 08-25-2007, 08:37 PM

I would suggest you replace the radiator hose...For good measure.

CamelotShadow · #14 09-02-2007, 09:05 PM

Ouch
Guess your lucky your temp is OK

exp tank seperated at seam
ut why does the hose look like it also has been exposed to severe pressure
or is also a weak walled defective part?

I did notice the 140 on thr radiator cap
is that the 1.4 bar

I have been trying to get a new cap myself
for my 83 500 SEC but my cap has 120 on it

I'm searching for specs on the rating of radiator cap for my car
My cap seems ok but car seems to run hot
NowI think it could be a faulty electrical connection or temp guage
Still a new radiator cap can't hurt
but I still need to confirm the pressure

Good Luck

juribe2 · #15 09-03-2007, 09:15 AM

So far so good with the new tank. I'm a little worried about that upper hose because it is less than a year old. I think that's a poor quality one because it the pressure cap is good, there can't be an overpressure in the system. I've tried 2 different caps and that hose keep the same.

I did a search on your car but only found 1984 500SEC and they offer both the 1.2 and the 1.4 caps with this comment:

1.2 Bar Although this number has been superseded to 124 500 01 060 (1.4 bar) it will continue to be offered as long as it is manufactured