94 sl500 5.0 engine. Car has been running hot for a while and I have been plying with this problem one step at a time. I noticed the upper hose collapsed this morning. Opened the radiator cap and the hose was fine. It is a new hose The T stat is removed. What would cause the car to pull a vacuum and hold it overnight?
... I noticed the upper hose collapsed this morning. Opened the radiator cap and the hose was fine. It is a new hose The T stat is removed. What would cause the car to pull a vacuum and hold it overnight?
When hot, coolant expands and goes to the expansion tank and when it cools down it should flow back to the radiator. The collapse upper radiator hose is caused by the coolant not returning to the radiator after cool down.
Why did you remove the t-stat? Did you replace the Rad hose with the appropriate MB hose? Without t-stat you'd have an unregulated coolant flow. Sudden change in coolant temp due to unregulated flow may have contributed to the cause of upper radiator hose collapse. Also, some aftermarket hose are not stiff enough to withstand MB sealed cooling system.
Don't know when was the switch over year, the newer cars does not have a coolant recovery tank, just the pressurized expansion tank. So if you overfilled the coolant, then when hot and expanded some coolant could escape via the pressure release and dumped onto the road. And when it cools down you have a vacuum in the system. That's why you should just fill the coolant up to the where the transparent part meets the black top of the recovery tank and leave some air in it.
here is a likely cause. Happens on not just MB vehicles. I had a similar problem with my silverado. The issue is that the cap on the expansion tank will vent with excess pressure, but also has to have a check valve to allow air back into the system when the engine cools down, water contracts so when cold there is no pressure or vacuum in the expansion tank. if the check valve gets plugged, you get the typical "collapsed upper radiator hose" symptom. this is also consistent with the hose returning to normal when you open the cap on the expansion tank.
solution: replace the cap on the expansion tank with a new one. I had to do this on my silverado and also my E-420 for the same symptoms. solved the problem.
The valve in the coolant tank cap is bad or not working. As described above, the cap isn't venting the system when it cools down. If this happens, a vacuum is created and the result is the hoses collapse.
The reason the hose collapsed is because there was air in the upper hose. It needs to be burped out. This is probably the reason your car is also overheating as the thermostat and water pump can not work properly/efficiently.
When the engine is hot, the air will expand and the hose will be inflated/hard. When the car sits over night, the air will contract and cause a vacuum and collapse the hose.
Water/coolant is not compressible! If hose is full with coolant, it will not collapse!
Yes, hose will not collapsed when the hose is full. The hose collapsed because some coolant that escaped to the expansion tank while it was hot didn't return to the radiator when it cooled down. This process created a vacuum that caused the hose to collapse.
Sure....................hose can collapse from bad cap, but odds are high that there is air in the upper hose since OP stated it is a new hose and T stat was removed.
Don't know about R129s, but the MBs I worked on with expansion tanks are a pain as far as purging air from the cooling system.
One easy way to test for air in the hose is by flicking your finger against it. Another is just slapping it with the palm of your hand if it is not pressurized.
Earlier MB's (e.g R107) does not have that hex bolt either, making air purge a 'popular' topic on that forum. You can purge air the hard way, parking the car in a steep hill etc. Search the R107 forum and you will find the procedure. It should be universal.
My 2011 E250 top hose does collapse over night.I constantly have to top the water up l have changed my stat top hose and bottle cap this still happens.Realy getting me down.l have had it tested for head gasket it's ok no gasses in the system help greatfully appreciated.
You have replaced the cap, so that rules out bad venting valve at the cap.
Does you car has a coolant recovery tank besides the expansion tank ?
Also did you top it all the way UP or just to the Max line ?
Hi the water level is correct to the marked line(upto the black section of the expansion bottle)It has in front of the bottle which l believe is a pump for the heater matrix??
Well, everything indicates there is vacuum in the system which means the Cap is not working properly. As you said you have replaced the cap, was that an OEM Cap from MB or just a generic one from Auto-Stores ? May be you should try another cap.
I have replaced the cap and this seems to have solved the problem,l will keep checking just in case.Thanks very much for your help with my problem.....
Hi it's me again my problem didn't go away it seemed to have sorted out but l was loosing fluid from my thermastat housing (top sensor houseing) so l purchased a new one,l went through the burping procedure and it seemed to have cleared now it is collapsing again have gone through the heater on full radiator lower than the pressure bottle revs 3500 for four minutes,not cured it more help needed please.
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Related Threads
?
?
?
?
?
Mercedes-Benz Forum
7.6M posts
693.6K members
Since 1999
BenzWorld.org forum is one of the largest Mercedes-Benz owner websites offering the most comprehensive collection of Mercedes-Benz information anywhere in the world. The site includes MB Forums, News, Galleries, Publications, Classifieds, Events and much more!