1999 e320 cdi expansion tank filler cap

Joined
Nov 23, 2008
Messages
3
Reaction score
0
Hi all, on sat ckeck coolant level warning was dispayed so i drove a mile home onlyto notice a slight leak under the car i topped up water to correct level,went to work the next day only to find a larger puddle .i then noticed the top hose from rad was completely flat so i undid the filler cap and the hose returned to normal .if i run the car with this slightly lose i do not have any water loss.so could the problem be the cap not allowing pressure decay and pulling a vaccumm when the engine cools down. the leak seems to be just above the water pump by the turbo.when the cap is tight.does this mean that when system is under pressure that water will find the weakest place to leak from. help much apreciated, Steve
 
Last edited:

television

Always remembered RIP
Joined
Mar 14, 2005
Messages
164,073
Reaction score
332
Age
86
Location
Daventry
Your Mercedes
2002 SL500, 216 CL500, all fully loaded
Hell and welcome,,,the most common fault is the water pump itself, where the gland fails, you can feel if any water of if it is wet underneath the front of the pump
 
OP
G
Joined
Nov 23, 2008
Messages
3
Reaction score
0
  • Thread Starter
  • Thread starter
  • #3
Thanks for a rapid reply,I drove home with the cap scewed on lose and there was no leak under the car,does this still point towords the pump or maybe still the pressure relief valve in the cap ,If it is the pump how easy is it to change.
 
Last edited:

television

Always remembered RIP
Joined
Mar 14, 2005
Messages
164,073
Reaction score
332
Age
86
Location
Daventry
Your Mercedes
2002 SL500, 216 CL500, all fully loaded
Yes it could still be the pump,,the cap being loose just stops the system pressurizing,,yes must check to see if it is wet under the front of the pump first
 
OP
G
Joined
Nov 23, 2008
Messages
3
Reaction score
0
  • Thread Starter
  • Thread starter
  • #5
hi malc sorry there is wet arround the pump but its not dripping ,is there any where on above where e leak may be,how does the gland inside the pump work or fail and would this cause the top hose to go flat when the engine is off cheers Steve
 

Alex Crow

Senior Member
Joined
Jul 9, 2009
Messages
10,677
Reaction score
40
Location
Super Suffolk
Your Mercedes
W169, W124, w202, W203, KTM 250 EXC, VW T25 camper and a Polo in a pear tree
if your top hose goes flat then, yes, it is likely to be the rad cap.

as malcolm says, the reason it does not leak with the cap off/loose is that it does not pressurise.

however, if you find yourself stuck in traffic on a hot august day with the cap off then expect the temp to go up and the coolant to come out!! it does not need to reach 100c on the gauge either, it will start to boil form a gauge reading of 90c or more due to localised hot spots around the cylinder head.
 

Alex Crow

Senior Member
Joined
Jul 9, 2009
Messages
10,677
Reaction score
40
Location
Super Suffolk
Your Mercedes
W169, W124, w202, W203, KTM 250 EXC, VW T25 camper and a Polo in a pear tree
i do agree with all you have said malcolm. leaving the cap loose avoids the pressure building that drives the leak, wherever it is from. from what the poster has said it does sound like pump gland failure

the last part of my previous post was a warning against running without the cap, ok for a get-you-home but a disaster in traffic!
 

wireman

Senior Member
Joined
Sep 20, 2005
Messages
2,632
Reaction score
3
Location
lancashire
Your Mercedes
nice 201 2.5D 1993 & very nice 129 SL500 1994
If the engine is hot the water that leaks will evaporate as it runs down the front of the engine from the drain holes in the water pump nose, you won't always see the coolant thats leaking, check it after its cooled down from normal temp a little and there is less chance of it drying up.

The top hose flatening is a give away for the pressure caps rubber seal being tired, they grow until they stick in the filler hole and a fairly strong vacuum can build up in the cooling system as it cools. They can also stick shut and then if the engine overheats and consequently over pressurises hoses can be blown off and radiators can be damaged, think safety valve.

To be sure that the cap is OK fit a new one it may be the real culprit, but from your post the pump gland is not in the best of condition.

If you intend to do the job yourself why not change the stat and cap at the same time.

Make sure that the coolant is new and at 50% anti freeze, failing to service the cooling system properly can cost you dear, the coolant has anti corrosion and lubricating propreties which degrade long before either the specific gravity of the coolant falls ( a common antifreeze test) or its ability to prevent freezing occur.

Horrible things happen to engines that are run for protracted periods without the protection that good coolant offers.

Two years is the max life for standard antifreeze, I dont bother with so called long life antifreeze.
 
Last edited:

Alex Crow

Senior Member
Joined
Jul 9, 2009
Messages
10,677
Reaction score
40
Location
Super Suffolk
Your Mercedes
W169, W124, w202, W203, KTM 250 EXC, VW T25 camper and a Polo in a pear tree
i'll second most of wiremans good post there. collapsed hoses = rad cap. the rad cap works two ways.....

1 - to maintain cooling system pressure up to a point (perhaps 1.5 - 2 bar?) and then allow venting of excess pressure.

2 - to allow air back into the system as the coolant cools, this function of the cap should open with only a very small pressure differential (perhaps -0.1 bar?)
 

AIB understand your special Mercedes deserves a special insurance policy. We have a refreshing attitude to insuring high performance, modified, imported or classic and vintage cars and deal with the UK’s leading insurers. We offer discounts for length of ownership, where the vehicle is kept overnight and limiting the mileage and can also cater for those clients who need higher mileage and business use. To obtain a quotation please call the team on 02380 268351 or visit us atAIB Insurance
Top Bottom