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  #16  
Old 03-27-2002, 05:47 PM
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The two I had where Wahlers, then I bought a genuine MB t-stat and the car runs cooler. Could be a bad batch if you've bought them from the same supplier. Try a different supplier or a different brand.

Brian

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  #17  
Old 03-27-2002, 07:16 PM
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Check the injection timing, and look for a bottom radiator hose collapsing under high flow conditions -- this restricts flow at speed and load, causing overheating.

Double check the thermostat installation -- I know it is a pain in the butt, and it something is restricting the valve opening, it may work fine and still not open all the way.

Do you have any pressure in the cooling system with a cold engine? If so, you have a cracked head or leaking head gasket.

Other than that, all I can think of is a flow restriction somewhere, and I can't think of a quick way to check that -- no cap on the rad.

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
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  #18  
Old 03-27-2002, 07:39 PM
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Peter - I think I am finally going to break down and pull the head on the 300D over the next couple weeks. It keeps pressure in the coolant reservoir a day after shutting it down from the day before (the 240D does not do this, neither does the Honda or E320). The 240D is running great (with a new front windshield and rear window seal as of this week and a new paint job scheduled at the end of April) so I am going to bite the bullet and see what the top end of the the 300D looks like. I am VERY reluctant to pull the head on a good running car but what the hey. I am "caught up" on my projects for right now so this looks like a good one. I will post pictures if I find anything worth showing.
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  #19  
Old 03-27-2002, 09:15 PM
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Henry,

You still have not answered Peter's question: Is there pressure in the cooling system when it is cold? In the morning, before you start it, squeeze the upper radiator hose. It should be SOFT, or even collapsed under vacuum. Open the rad cap, it should not "pop" as if there is pressure present. If all that is AOK, go drive the car HARD - lots of full throttle runs to the redline. DO NOT open the radiator cap. Now repeat the same test the next morning - there should still be ZERO pressure in the system. If there is pressure (upper hose tight, cap "pops" when you remove it) then you will need to pull the head (again). I just got done doing this on my car (search this forum for topics posted by me in the last 2 months).

Forget messing with the thermostat. I have read over and over where people go through 2, 3, 4 or more with this kind of problem. It ain't it. Don't drill holes in it. And do NOT remove it! Mercedes designed the car to run with it in place, when you remove it, very little coolant is sent through the radiator - meaning you could overheat it AGAIN. I'm assuming you have either a dealer t-stat or a decent German made one, correct? No "Made in China" stuff from McParts?

Oil - running synthetic is great, but should have absolutely NO effect on this problem. Your car should run at 85-90C regardless of oil. You are trying to kill a mammoth with lawn darts here. Last question - how old is the radiator? And is it an OEM aluminum Behr? I had one plug up and cause serious hot running and it was only 3 years (and ~40kmi?) old! Changing it cured my problems (along with a new fan clutch), now the car refuses to run over 100C even in 110F ambient temps, freeway OR idling. Normal winter temps are 85-90C on the dash gauge.


I still think you have cracks in your head that were missed in the "presure test". Was it magnafluxed? Anyway, check out photos of my head replacement job, and the cracks in the head (cyls 5 & 6), here:

http://www.meimann.com/images/mercedes/head_gasket/


Keep us posted!
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  #20  
Old 03-27-2002, 10:18 PM
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Dave, With all due respect, why can it NOT be the thermostat? My 1987 300D ran one needle width below 100C (98C) in 39F weather on the freeway before a new radiator and after. I boiled my first and second thermostat's (Wahlers) and they opened and closed at the same time. With a third thermostat the car immediately ran at 90C and only gets to 93C a low speed with heavy load.

How does one check the lower rad hose under load to see if its collapsing? My upper rad hose used to collapse so I purchased a new expansion tank cap and the problem went away. I replaced the upper rad hose just to be safe. I plan to replace the lower rad hose soon, to be safe.

Brian
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  #21  
Old 03-27-2002, 11:06 PM
bobco
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Exclamation running to hot

acts just like mine did when i got the stat in backwards. Bob se,ks.
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  #22  
Old 03-27-2002, 11:58 PM
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Brian, it's just *highly* unlikely (IMO) that you'll get multiple "bad"thermostats. You said the first two (Wahlers) operated the same. What brand is the third? A miscalibrated aftermarket unit could be masking a more serious problem if the first 2 units were good per MB specs... i.e., you got the needle down, but is there something else wrong? I installed a Wahler in my sister's 1987 300D recently and it runs at 85-90C all the time. If you got a 3rd Wahler that changed things then that leads me to believe we shouldn't be using them, now should we!

Another note: Theses cars (1987 300D) are VERY finicky about filling with water fully. It helps to jack up the passenger side as high as you can when filling. Then run the heater on "high" until you get hot air from the vents, and keep an eye on the gauge. Often it will cross 100C before the t-stat opens and the air pocket gets purged, then it drops to normal (85C). Also, I once had trouble for weeks with the upper hose collapsing when it was cold. Eventually it went away, I think there was an air pocket that finally worked itself out. There was no problem with cooling, just the hose visibly flattened (when cold).



Um, Bob - it is impossible to install the t-stat in this engine backwards. It only fits ONE way. You cannot fit it into the housing the other way. Trust me. :p


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  #23  
Old 03-28-2002, 12:38 AM
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Dave, the third thermostat was a MB dealer thermostat. Yes, it could be bad and opening too soon. I'm trying not to be pessmisstic. I keep an eye on the coolant expansion tank and hoses and the level hasn't changed nor have any hoses collapsed. I was able to put back the amount of coolant I took out. In the past I have gotten only 1/2 in, knew there was an air bubble and was careful to not overheat the car while adding the rest of the coolant. I haven't tried jacking up the car yet, but next time I will give that a shot and make sure the heater is on max too. I figure that 90C is halfway between 80C and line between 80 and 120.
Brian
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  #24  
Old 03-28-2002, 07:14 PM
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Jim:

I just passed on a 1980 300D with a leaking head gasket that caused cooling system overpressure and eventual overheating -- leaking compression into the cooling system from one cylinder.

That wasn't a problem, but the floor was rusted through on both sided and the driver's side rear fender was perforated in a couple places -- I already have a rustbucket, I don't need another one!

I assume you have replaced the radiator cap with a new factory one and are still having the problem. If so, you may very well have a head gasket going -- not a big problem if you've got a helper to haul that head around -- it's heavy!

I'm also going to look at a 1980 300D (listed at $1900) in the next week or so -- I think I'm about to become an independent contractor and will need a cheap transportation device.

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #25  
Old 03-28-2002, 07:29 PM
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Yes the radiator, water pump and radiator cap are new and the car runs out great. It does have a single "miss" on cold start up after it has been sitting for a week or so but I feel that may be an issue with the valve adjustment (it is time) or the fuel filters. I will say that it runs slightly cooler (based on the gauge) than the 240D - especially on the interstate. On the 300D the needle NEVER gets over the top edge of the 8 on the 80 number.
Before I pull the head - just for the heck of it - I think I will swap the radiator caps on the 240D and the 300D and see what happens.
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  #26  
Old 03-30-2002, 02:30 PM
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I took a look at the photos and re-read all the threads. If the head was cracked, it did not show up on the pressure test. The head was not magnefluxed. I wish I had it done. I was not aware that magneflux would work on a non magnetic metal. I just went out to check if the cap was pressurized when it is cold and it gave a slight whoosh sound when I opened it. I will perform the run hard test and check it again in the moring. I do agree that removing the t-stat is not the answer and I hope i did not spend money on the valve job for not. I do now that I did check the head for cracks very carefully and I can say that I had no cracks as is shown in the photo's. Is it possible that the cracks are intergral to the head and not visible? I will bleed the car as you recommend and see what happens. I will let everyone know the outcome.
henry
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  #27  
Old 03-30-2002, 02:33 PM
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I forgot to mention that the radiator is 6 months old and it is a Behr aluminum radiator. All parts are OEM with the exception of radiator fluid. That can not be the problem. This car never ran hot until I overheated it in conjunction with a poor bleed job after I replaced hoses, radiator and t-stat.

henry
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63 190d (sold)
69 220D (sold)
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76 BMW 2002 (sold)
86 190E-16v (Demised at Laguna Seca Turn 9)
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87 300SDL 135k
87 300TD 280k (sold)
95 E320W 211k
95 E320w 111k
05 C320 4matic
06 E320 CDI 90k (Totaled by a texting 19 year old girl in a nissan)
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  #28  
Old 03-30-2002, 02:43 PM
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Hi Henry,

Hmm, this is all very strange. Be careful you're not reading more into the "whoosh" sound than is really there. The more definitive test is the radiator hose. It should be quite soft when cold. When there is the high pressure problem, it is so tight you can't squeeze it together (to make the opposite walls touch) unless you're Schwarzenegger or Stallone. ;D

On my car, with the high pressure, it's not a gentle little "whoosh" sound. It's more of a "POW!" when the pressure releases. If you have little to no pressure when cold, your head & gasket are probably OK. And in that case I'm low on ideas, it sounds like you're replaced almost everything possible!

Have you checked the dash gauge, to make sure it's reading properly? A new sender wouldn't cure that...!


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  #29  
Old 03-30-2002, 04:02 PM
HGV HGV is offline
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Dave, thanks for the advice. I agree with your "woosh" analogy and I will pay more attention to the hard or soft hose approach. No one has mentioned the auxilary fan. It seems to never come on. AC on, off, engine temp hot cold, never comes on. What turns it on? I will check the temp gauge in the dash. I recall reading in the manual a procedure to test it.

Henry
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63 190d (sold)
69 220D (sold)
69 280SL (sold)
76 BMW 2002 (sold)
86 190E-16v (Demised at Laguna Seca Turn 9)
87 300SDL (sold)
87 300SDL 135k
87 300TD 280k (sold)
95 E320W 211k
95 E320w 111k
05 C320 4matic
06 E320 CDI 90k (Totaled by a texting 19 year old girl in a nissan)
2013 GLK 250 Bluetek 4MATIC
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  #30  
Old 03-30-2002, 04:39 PM
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Hi Henry,

1- I just thought of something else, although it's highly unlikely given the timing of your problem. Have you cleaned out your A/C condensor fins? The radiator should be clean since it's almost new, but the condensor could be filled with bug guts & other crud, drastically reducing airflow to the radiator. High pressure water from the local car wash works good to flush it out, and/or compressed air. It's preferred to do it from inside out but that's a real PITA.


2- The aux fan is another interesting story. First, let me say that it's not your problem. The car should run cool regardless of the aux fan. It is there for extreme heat conditions and to help the A/C cool better, not for "normal" engine cooling. It has 2 speeds. The high speed only engages from the 3-prong temp switch up at the water neck, by the upper radiator hose. It is supposed to turn the fan on high at 105C. The low speed only engages from a switch on the A/C receiver/dryer. This turns on when the refrigerant high pressure reaches a certain pressure. There are 2 different switches. Older cars, like yours, have the green switch - which is rated at something stupid like 20 bar, so the fan almost never runs. Later cars (1990-up?) have a red switch, which engages the fan at a more reasonable 16 bar, so the fan runs most of the time the A/C is on. You can retrofit yours to the red switch, BUT you have to evacuate & recharge the A/C system, which is a PITA (and expensive). You can verify the fan itself by shorting the two pins on the 105C temp switch, this should make the fan run on high. Shorting the leads at the green (or red) switch will make it run on low. There's also a relay in the circuit, so if the fan doesn't work, check the fuses and the relay.


HTH,

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