Upper radiator hose collapse--- Overheating E420

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I did a pressure test on my E420's cooling system and found a leak in the upper radiator hose where it connects to the engine. It didn't leak fluid before, but with about 20lbs of air pressure, I heard air
hissing out of the top near clamp. I re-tightened clamp and air leak stopped. Went on road test and car still heated up, but when I stopped car and it cooled for a while, I checked hose, it had collapsed flat.
When car was running and hot the upper hose was full and tight; I noticed the lower elbow hose connected to the thermostat seemed ballooned.
Does the above point to a water pump or thermostat issue? or both
Thanks, Derf
"If at first you don't succeed, you succeeded with failure."
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Follow-up--- After a couple cycles of on and off and adding additional fluid, the last 5 mile test ride car stayed cool, well under the 100c mark. I think IT'S FIXED.................. WOOOOOOOOOOOHEEEEEEEEEEE!!!!!!!! (no party yet till later highway test)
The collapsed hose was the engine vacuum that wanting more fluid....still going to replace puffy elbow hose....
I made a homemade cooling system pressure tester with a bicycle foot pump (with gauge) connected to the overflow tube going to the radiator (used rubber gas hose that fitted inside overflow tube at one end and slipped over foot pump air nipple). I just blocked the overflow hose nipple at the overflow reservoir with a short piece of hose, clamped to nipple, and with a bolt screwed in open end of hose, as a stop. This test is great because it tests the cap too! MB's factory pressure tester has a modified radiator cap that is used and you have to remove your existing cap to test.
As much as I'm learning about my MB, I hate to even think about selling it.... This car cost $54,000 new in 1994 (I paid a fraction) and drives smoother than new. I tried the newer series E models 96- later and they don't drive/feel like the original W124 series or older MB classics.....also the design of newer MBs you have to see MB logo to know it's a Mercedes... the classics stand out as MBs without a doubt....
I'll post a follow-up after highway test....
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If the top collapse and the bottom seems like a baloon, I suspect your radiator is clogged... coolant cannot flow as easily.
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After highway test, engine stayed cool longer but eventually heated up. Ballooned hose was defective (split inside and outer rubber skin was barely holding fluid and eventually sprung a dripping leak). Also did another pressure test and same upper hose was releasing air. I replaced ballooning hose and upper hose. Rechecked pressure and refilled with fluid. Now I'm awaiting a couple cycles of on and off to see results.
One thing I did notice is that after heat up, radiator was cool in center, but when I turned on cabin heat to circulate coolant, radiator center became hot... not sure what that indicates??? I guess that rules out clogged radiator???? Unless radiator is clogged at top where fluid returns from engine???
Stay tuned for next road test after a couple of on and off cycles....
Derf
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Forgot to mention that the ballooning hose was not at bottom of radiator but is small elbow that attached to thermostat housing....
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The saga continues.... Car still overheats after 20 minutes or full warm up...Drives great until that point... ...upper hose still collapses after cool down. I think Tiger might be right about radiator clog, but why would loosening rad cap release vacuum even when I pinched close upper overflow tube leading to collapsed upper hose...shouldn't rad cap release vacuum without loosening it?
My overheating problem may be a clogged catalytic converter. When cold the cat has not expanded fully and when hot closes up creating back pressure... Anyone know of clogged cat causing overheating?
Also, I noticed the main overflow tank has it's own overflow tank with a vacuum line attached. What's that about? Could that be the culprit?
All help truly appreciated...Derf
"Wisdom is gained by determination."
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| The saga continues.... Car still overheats after 20 minutes or full | warm up...Drives great until that point... ...upper hose still | collapses after cool down. I think Tiger might be right about radiator | clog, but why would loosening rad cap release vacuum even when I | pinched close upper overflow tube leading to collapsed upper | hose...shouldn't rad cap release vacuum without loosening it? | | My overheating problem may be a clogged catalytic converter. When cold | the cat has not expanded fully and when hot closes up creating back | pressure... Anyone know of clogged cat causing overheating? | | Also, I noticed the main overflow tank has it's own overflow tank with | a vacuum line attached. What's that about? Could that be the culprit? | | All help truly appreciated...Derf | | | "Wisdom is gained by determination."
I think you have a thermostat that is stuck in the almost closed position. I've seen that symptom before and the thermostat was stuck.
Partially plugged catalytic convertors cause loss of power, not overheating.
Just my 2.
--
Steve Spence
Independent AMSOIL Dealer
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Thanks Steve... I did the thermostat in pot of heated water test and it opened up (1/2") at around 80c, but now that you mentioned it, that test only shows large round plate opening at base plate and not the operation of the smaller round springed plate at opposite end of base (which controls flow from engine)...... hhhhmmmmmm....
I did install a new thermostat (and still had overheating so I put back old one) but that was before I had discovered a leak in top hose, through a pressure test. When I swapped out the old thermostat, during my diagnostics, I removed upper radiator hose and it didn't seal properly, compounding my problem.... sounds logical.
I'll swap old thermostat with new one and keep everyone posted
(below link is a coolant flow diagram I've been using as a reference)
http://home.comcast.net/~phantoms/vacuum/coolant_flow.jpg
Thanks to all.... Derf
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Clogged cat converter will raise engine operating temperature. No question about it. How hot is your engine running?
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It would hang at 120c and red line at stops, then when moving temp dropped just under 120 mark.
I borrowed a cooling system pressure tester that tests caps and found that the new cap (and old cap) weren't consistently holding pressure during different tests (newer cap would hold sometimes, old cap nada) ugh! So I'm getting a replacement today.
Also, with pressure tester attached to overflow tank it was holding pressure and car stayed at normal temp. Didn't get any blow back either (a good sign).... I think I'm close to nailing this snafu.... Look for update
"If man can build a car, man can fix a car."
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I doubt a faulty coolant cap would produce the overheating that you are experiencing. Having the thermostat out, and thermostats being cheap, I would have replaced it regardless of what the water pan test showed. It's possible it's hanging up somehow when it's actually in the car.
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You are thinking of three way cat converters with bypass tubes that feed back to EGR system. Alot of older MB does not have that. They have one way cat system... no bypass.
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Are you aware of the fact that Mercedes 3 liter diesel thermostats have to be aligned when put in? There is a small hole in the rim of the thermostat which has to be aligned with some sort of mark in the housing. I can find that in the manual and send you a scan of the picture if you don't know about it and can't figure it out.
If your thermostat is not aligned properly it won't open completely and the engine will run hot at speed or on a grade, etc.
Paul
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There's a hole in my thermostat's base plate with a tiny bb within a tube that acts like a flow check valve (no hole at rim). I read somewhere it needs to be at the top, 12 o'clock? (someone please confirm).
Update: Put on newly bought cap that passed pressure test of 20lbs (Mercedes dealer wanted $29 for cap and Autozone wanted $5) I'm now going through cycling/burping process. Noticeable improvement on first highway test (car ran at 100c at highway speed and under 110c in stop and go traffic (never reached 120c). I read that it takes a couple of cycles to fully bleed coolant and should eventually purge all air traps. Future test drives hopefully will show cooler results....Stay tuned
Car idles around 750 RPM in neutral with just under 1 bar oil pressure after warm up...
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Something is clearly wrong here. If cars needed multiple road trips to bleed air and avoid overheating, a hell of a lot of cars would be overheating following coolant changes and similar. I've also never seen a car overheat during normal driving around town from a bad radiator cap.
The notion that every last bit of air has to be out of the system or the car will overheat doesn't make sense. Years ago, cars didn't have expansion tank reservoirs and the radiator cap and fill was on the radiator itself. The rest of the cooling system was very similar to what you have today. It was not unusual to see coolant level down a couple of inches back then and these cars did not over heat.
I suspect you have either a plugged radiator, a faulty thermostat, or less likely a water pump that has disintegrated. I haven't seen the last one, but someone did report on this topic that they had seen one where the impeller had disintegrated.

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Did you wash your radiator? Use air or water... from engine side out to the front of the car... to dislodge any bugs and dirts that may be trapped.
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I pressure cleaned rad from inside to out a few days ago. The cheapy rad cap I bought from Azone had a slow leak (released pressure at 20 psi but would fall back to 17/18 psi and slowly leaked) so I found a MB dealer with MB one for 15 bucks and exchanged it (it held pressure at 20 psi). Put MB rad cap in and car tested and took longer to get hot no red line but close only at stop and go driving (high speed it was just above 100c mark). Radiator was too cool in center for as hot as car got... It's all pointing to water pump or radiator... not sure how to check water pump???? without removing it... Is there a way to inspect impeller without removing it??? Maybe removing thermostat or upper hose and using a dental mirror???
Thanks, Derf
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Derf-E420-94 ha scritto:

Mmm... if the radiator tubes are clogged there cold be a much hotter and cooler side of the radiator. I mean: if fluid flows correctly, the two hoses will have a different temperature, but not that BIG difference. While, if the pump is involved, the fluid will flow slowly thus resulting in a quite uniform temperature (hot!) in radiator and hoses from/to engine. Is it this a thought that might help you to find a correct procedure to find out if the problem is a clogged radiator or a weak water pump? I hope so... I can tell you that old mechs used to touch radiator and hoses to correctly diagnose the problem...
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