300SEL 3.5: coolant is disappearing - PeachParts Mercedes-Benz Forum

werminghausen · #1 03-18-2013, 02:24 PM

I have cleaned my radiator some time ago (changed coolant at the same time), I also changed cylinder heads and now after a couple hundred miles engine overheated at idle. Coolant was very low. I had to add 3 liters. I was checking coolant level today and I am definitely loosing coolant.
However I am not seeing any water leaking externally...nor do I see white puffs (head gasket) nor do I see anything in the engine oil.
So where is the coolant going?

I saw today that coolant was very milky...As I used Toyota red coolant I am puzzled how it can get whitish/milky?

Any ideas?
Martin

werminghausen · #2 03-19-2013, 12:26 PM

How would you do a pressure leak down test?
What location/port do I use for the pressure test?
What is an acceptable pressure drop, what not?

Frank Reiner · #3 03-19-2013, 02:59 PM

Martin:

Consider the possibility that there is a one way, small head gasket leak.
The cooling system will be pressurized above its usual operating pressure (~15psi), the hot combustion products will create steam at the point of the leak, and water will be forced out of the radiator overflow. The combustion products may also interact with the dye in the coolant to turn it milky.

werminghausen · #4 03-20-2013, 11:05 AM

Quote:

Originally Posted by Frank Reiner

Martin:

Consider the possibility that there is a one way, small head gasket leak.
The cooling system will be pressurized above its usual operating pressure (~15psi), the hot combustion products will create steam at the point of the leak, and water will be forced out of the radiator overflow. The combustion products may also interact with the dye in the coolant to turn it milky.

Thanks Frank,
true...but I have changed the head gaskets...I hope it is not head gasket Another option would be a slight external leak, say at the hose.. when there is pressure on the system and engine hot... any leak (meaning small amount of coolant) could land on hot engine part and vaporize before it reaches the ground.
If engine is getting colder the pressure is gone and system is tight again.
Well also in Oman the street is always very hot, even the garage floor, and thats why I probably never see anything on the floor.
Any chance to tackle and get the problem sorted out?
I am thinking first thing will be an elaborate pressure test.
How much pressure drop is normal?

Frank Reiner · #5 03-20-2013, 01:07 PM

Martin:

Are you familiar with cooling system pressure testers such as this:

Stant St 255 Cooling System Pressure Tester in Case | eBay

There are various versions of such a device for pressurizing the system, but all allow you to pump up to the desired pressure and observe any change on the gauge. An intact system will hold the set pressure for many hours, affected only by changes in temperature.

The gauge on the tester will also display any increase in pressure when the engine is running; a rapid increase may indicate a head gasket leak into the cooling system.

alabbasi · #6 03-20-2013, 01:20 PM

It sounds to me like you have either a head gasket or intake manifold gasket leak. It may be slight.

The pressure tester would be one way of testing it as it will either force coolant out of it's leak point if it's external or into the block, thus causing a pressure drop.

Another means to test for HG leaks is to the chemical block testers like the one below:

http://www.ebay.com/itm/Cylinder-Head-Gasket-Block-Tester-Kit-/221147093962#vi-content

werminghausen · #7 03-20-2013, 01:44 PM

Quote:

Originally Posted by Frank Reiner

Martin:

Are you familiar with cooling system pressure testers such as this:

Stant St 255 Cooling System Pressure Tester in Case | eBay

There are various versions of such a device for pressurizing the system, but all allow you to pump up to the desired pressure and observe any change on the gauge. An intact system will hold the set pressure for many hours, affected only by changes in temperature.

The gauge on the tester will also display any increase in pressure when the engine is running; a rapid increase may indicate a head gasket leak into the cooling system.

Thanks, as I am in the middle of nowhere..no ebay, no nothing.... I have a plan to build my own pressure tester. I'll kill an old temp sensor and solder hose connection to it for a pump and put it in the M14 thread of the temp sensor for the aux fan, then pump up to 15psi...watching what is going on here....

I'll report back.

werminghausen · #8 03-20-2013, 01:46 PM

Quote:

Originally Posted by alabbasi

It sounds to me like you have either a head gasket or intake manifold gasket leak. It may be slight.

The pressure tester would be one way of testing it as it will either force coolant out of it's leak point if it's external or into the block, thus causing a pressure drop.

Another means to test for HG leaks is to the chemical block testers like the one below:

Cylinder Head Gasket Block Tester Kit | eBay

Hi Al,
still hoping it is not the head gasket or manifold. Keep fingers crossed.

werminghausen · #9 03-21-2013, 01:26 AM

I am very positive that I found the leak. I built my own pressurizing tool ...a pump and connection to the temperature switch (aux fan) the pumped up to 15psi...radiator is leaking at the connection to the upper fat rubber hose. First I thought it is the rubber...but then I found out it is the solder joint at the connection.
So I need to resolder....
has anyone done this before..I mean how great are chances that I mess things up rather than repair?
How would you solder this part? Can I do it in the upright position or do I need to remove the radiator?
Martin

alabbasi · #10 03-21-2013, 05:54 AM

Take the radiator to a radiator shop and have them do it. That was one of the first repairs that I had to do when I bought my 280sel 4.5

werminghausen · #11 03-21-2013, 07:34 AM

I'll try and hard- solder (brazing) the the radiator neck myself as I have done some plumbing work before I have the stuff (I make my pressure connection with an old temp sensor and a copper pipe for pump and gauge)..if this fails I'll take it out to a radiator shop. I'll report back .

alabbasi · #12 03-21-2013, 07:45 AM

Martin, if you ever get stuck in an Omani prison, I expect to hear about an "A Team" style escape in the news

Mike D · #13 03-21-2013, 08:55 AM

In the news? Heck, Martin will probably give us a step by step account as it happens.

"Now as I am removing the bricks, would it best to use an offset method or should I go for a square block removal?"

Just as in any soldering, cleanliness is the key. Wire brush the metal spic and span and use flux freely.

alabbasi · #14 03-21-2013, 09:21 AM

Quote:

Originally Posted by Mike D

In the news? Heck, Martin will probably give us a step by step account as it happens

or leave the blueprints behind

Tomguy · #15 03-21-2013, 12:05 PM

I repaired my 4.5's radiator myself and the repair lasted about a year before weeping began again (I didn't think the repair would work honestly so I just did a rush job). When I tried to repair it the second time I made it worse so I got a replacement radiator. Clean it well, do a good job and you'll have no issues!