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  #1  
Old 01-25-2011, 03:33 PM
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Cooling System Riddle 1991 350 SDL

1991 350 SDL with an engine out of a 1987 300D

I drove the engine donor vehicle 400 miles home with no overheating or coolant loss problems.

After it was transplanted into the SDL, the cooling system is pushing coolant out of the reservoir into the overflow container in the fender well. It does not overheat unless it pushes enough coolant out to be low on coolant. It does this at freeway speeds above 65. Below 65 it does not seem to do it. It can take 75 miles of freeway speed before it pushes out enough for the low coolant warning light to come on.

All coolant missing from the cooling system can be accounted for by the coolant in the overflow container. There are no external leaks.

It is pressurizing the cooling system enough to push coolant out the 20lb cap, but not overheating to do it. It must be combustion gases. I have tested for combustion gases in the cooling system and found none. I used a Uview 560000 Combustion Leak Tester. I have used this tester after every trip since I got it and it has never indicated combustion gases. I was so sure it was combustion gases that I tested the tester by sniffing the exhaust at the tail pipe and found that the tester worked as it was suppose to.

There is no steam, no white smoke, and no anti-freeze odor in the exhaust.

I have tried running an unpressurized cooling system by removing the return valve on the bottom of an old reservoir cap so all expansion gases can pass out to the overflow tank. It will still eventually push out enough coolant for the low coolant warning light to come on.

It has a new radiator
new reservoir cap
swapped out the coolant reservoir from an SDL with no cooling problems
fixed all coolant seepage, there are no leaks
the thermostat operates as it should
the fan and fan clutch work as they should
the heating system works and there is no anti-freeze odor

I have 2 temp gauges, the stock one and one with a sensor at the return end of the coolant loop that heats the VO fuel line and the filter in the trunk. Both gauges confirm that the cooling system does not get above 180 -190 range while this is happening. When enough coolant is pushed out, the VO loop gauge will fall as the loop goes dry and the stock gauge will start to rise as the system becomes low on coolant. I have never let it overheat.

If it is not overheating
If no combustion gases are detected in the coolant system
What could pressurize the coolant system enough to do this?

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Greg
2012 S350 BlueTEC 4Matic
2007 ML 320 CDI
2007 Leisure Travel Serenity
2006 Sprinter 432k
2005 E320 CDI
1998 SLK230 (teal)
1998 SLK230 (silver)
1996 E300D 99k, 30k on WVO
Previous:
1983 240D, on WVO
1982 300D, on WVO
1983 300CD, on WVO
1986 300SDL 237k, 25k on WVO (Deerslayer)
1991 350SDL 249k, 56k on WVO - Retired to a car spa in Phoenix
1983 380 SEC w/603 diesel, 8k on WVO
1996 E300D 351k, 177k on WVO
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  #2  
Old 01-25-2011, 03:37 PM
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... put a new radiator cap on it
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1996 s10 zr2 with a 6.5 turbo diesel
1996 c2500 suburban with a 6.5 turbo diesel
1981 300sd with a turbo 617
Monte carlo figure 8 car
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  #3  
Old 01-25-2011, 03:42 PM
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Quote:
Originally Posted by josha37 View Post
... put a new radiator cap on it
As noted in the post, it has one.
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Greg
2012 S350 BlueTEC 4Matic
2007 ML 320 CDI
2007 Leisure Travel Serenity
2006 Sprinter 432k
2005 E320 CDI
1998 SLK230 (teal)
1998 SLK230 (silver)
1996 E300D 99k, 30k on WVO
Previous:
1983 240D, on WVO
1982 300D, on WVO
1983 300CD, on WVO
1986 300SDL 237k, 25k on WVO (Deerslayer)
1991 350SDL 249k, 56k on WVO - Retired to a car spa in Phoenix
1983 380 SEC w/603 diesel, 8k on WVO
1996 E300D 351k, 177k on WVO
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  #4  
Old 01-25-2011, 03:45 PM
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Unless you are blowing radiator hoses up it is either not sealing or is not strong enough. Me and the master tech next to me say... put a new cap on it. if you really need something else to check have a assistant put it in gear and put a load on it while you check for exhaust gas in the rad.
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1996 s10 zr2 with a 6.5 turbo diesel
1996 c2500 suburban with a 6.5 turbo diesel
1981 300sd with a turbo 617
Monte carlo figure 8 car
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  #5  
Old 01-25-2011, 03:45 PM
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Do you have before photos to ensure that the hose routing is correct?
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  #6  
Old 01-25-2011, 04:15 PM
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Quote:
Originally Posted by josha37 View Post
Unless you are blowing radiator hoses up it is either not sealing or is not strong enough. Me and the master tech next to me say... put a new cap on it. if you really need something else to check have a assistant put it in gear and put a load on it while you check for exhaust gas in the rad.
Thanks for your responses.

Caps (3) have been swapped from systems with no issues.
A new cap has been installed.
A replacement reservoir from a system with no issues has been installed even though the original one tested tight.

But...with your encouragement, I will have the brand new cap tested.

Thanks
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Greg
2012 S350 BlueTEC 4Matic
2007 ML 320 CDI
2007 Leisure Travel Serenity
2006 Sprinter 432k
2005 E320 CDI
1998 SLK230 (teal)
1998 SLK230 (silver)
1996 E300D 99k, 30k on WVO
Previous:
1983 240D, on WVO
1982 300D, on WVO
1983 300CD, on WVO
1986 300SDL 237k, 25k on WVO (Deerslayer)
1991 350SDL 249k, 56k on WVO - Retired to a car spa in Phoenix
1983 380 SEC w/603 diesel, 8k on WVO
1996 E300D 351k, 177k on WVO
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  #7  
Old 01-25-2011, 04:16 PM
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it could be as simple as your using the wrong one for that rad so the sealing surfaces dont meet. Does it ever hold pressure?
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1996 s10 zr2 with a 6.5 turbo diesel
1996 c2500 suburban with a 6.5 turbo diesel
1981 300sd with a turbo 617
Monte carlo figure 8 car
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  #8  
Old 01-25-2011, 04:41 PM
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Quote:
Originally Posted by josha37 View Post
... put a new radiator cap on it
X3.

We have seen this condition on race cars. Start to puke after x minutes, new parts list like yours. Often we try yet another 'new' cap and it works. In some cases we go so far as to use a heavier cap. (Not that it physically weighs more, but the pressure rating is higher).

have you tested the cooling system pressure (with the "new" cap installed) and note at what point it starts to push fluid? Perhaps the pressure is hitting 15psi, pops the cap and then pushes fluid out. The indicated pressure should then be even lower as the system evacuates.


this may sounds crazy, but are the water pumps any different between the two motors? rads different? Hoses different?

What direction does the water pump turn on each motor?
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84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.
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  #9  
Old 01-25-2011, 04:47 PM
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With a real cooling system issue i would expect him to complain of over heating (hoses water pump direction). My vote stays cap.
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1996 s10 zr2 with a 6.5 turbo diesel
1996 c2500 suburban with a 6.5 turbo diesel
1981 300sd with a turbo 617
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  #10  
Old 01-25-2011, 04:51 PM
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Just had these exact symptoms on a buddy's diesel Jetta -- it, too, was the radiator cap. The o-ring was missing. A new cap (and o-ring) fixed the matter completely. Maybe you just happened to get three bad caps!?!?
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  #11  
Old 01-25-2011, 04:56 PM
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I'm thinking radiator cap also. You need to get a reading on actual pressures in the system when this is happening.
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
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  #12  
Old 01-25-2011, 05:06 PM
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Thanks for all your responses.

The cap held 30 psi in the tester. Seems to be quite a bit for a cap rated at 20 psi.

I will order a new cap anyway. It will be here tomorrow morning.
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Greg
2012 S350 BlueTEC 4Matic
2007 ML 320 CDI
2007 Leisure Travel Serenity
2006 Sprinter 432k
2005 E320 CDI
1998 SLK230 (teal)
1998 SLK230 (silver)
1996 E300D 99k, 30k on WVO
Previous:
1983 240D, on WVO
1982 300D, on WVO
1983 300CD, on WVO
1986 300SDL 237k, 25k on WVO (Deerslayer)
1991 350SDL 249k, 56k on WVO - Retired to a car spa in Phoenix
1983 380 SEC w/603 diesel, 8k on WVO
1996 E300D 351k, 177k on WVO
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  #13  
Old 01-25-2011, 05:10 PM
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Coolant is not going to displace itself with air. Either there is a local hot spot in the engine, or air is being introduced to the suction side of the system, which could then lead to a hot spot.
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  #14  
Old 01-25-2011, 05:16 PM
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but at higher engine speeds, the cooling system should self bleed.

Am I wrong?


But clearly, if the system is NOT self bleeding, I would try to find out why.
__________________
83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.
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  #15  
Old 01-25-2011, 05:24 PM
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quick question.. have you pressure tested the system? a leak on a suction side would be plausible of you fuel heater circuit is on the suction side of the heater core.. i still think cap.

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1996 s10 zr2 with a 6.5 turbo diesel
1996 c2500 suburban with a 6.5 turbo diesel
1981 300sd with a turbo 617
Monte carlo figure 8 car
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