yep, and while the old 3 gal 'merkun systems (64 shovey reference) could
run without a radiator cap, the 123 on can't. The 124 and 126 on
cooling systems are designed to run at higher temps and under pressure
to work right. There is no longer any excess capacity in the system, as
evidenced by overheating if the radiator gets a little plugged, or if
either fan does not work right.
Same t'ing if you have a 210, 211, 140 129 etc newer vehicles.
fmiser via Mercedes <mailto:mercedes@okiebenz.com>
May 28, 2016 at 5:25 PMvia Postbox
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Dan Inquires:
Why would leaving the cap off to ostensibly prevent
pressure from building up, much as one does in a
vergasser, not work the same way in a diesel?
Rick replies:
Here's a couple links, one is more engineer friendly (dry
reading), that may help explain the phenomenon. There is no
direct statement "the coolant system must be pressurized",
At it's most simple, the higher pressure means higher boiling
point which means less likely to vaporize coolant.
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Rick Knoble via Mercedes <mailto:mercedes@okiebenz.com>
May 27, 2016 at 9:02 PMvia Postbox
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I figured "coolant cavitation". I did a little research, and I think
my suspicions are confirmed.
Basically, a diesel hammers so hard when a cylinder fires, without
proper coolant, properly
pressurized, coolant will form high pressure bubbles (cavitation) at
the cylinder walls.
In some engines it will eventually erode holes in the head and/or
cylinder wall. I suppose
this is why A. Marshall Booth (rip) was adamant on using proper
coolant, and changing
it on a schedule, although he never did (that I recall) explain WHY.
Here's a couple links, one is more engineer friendly (dry reading),
that may
help explain the phenomenon. There is no direct statement "the coolant
system must be pressurized",
but I have come to that conclusion from the information and my own
personal experience.
http://penray.com/cooling-system-techfacts/cavitation-in-cooling-sytems/
http://www.cruisingworld.com/how/engine-cooling-system-tips
http://www.concentricab.com/Press-Release-Detail.asp?k_id=141&cat=8&subcat=81&subsubcat=812&subsubsubcat=812
RIck
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Dan Penoff via Mercedes <mailto:mercedes@okiebenz.com>
May 27, 2016 at 8:18 PMvia Postbox
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So silly question time:
Why would leaving the cap off to ostensibly prevent pressure from
building up, much as one does in a vergasser, not work the same way in
a diesel?
And again, thank you!
Dan
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Rick Knoble via Mercedes <mailto:mercedes@okiebenz.com>
May 27, 2016 at 7:41 PMvia Postbox
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Dan inquires:
I had not secured the radiator cap with the intent that if there were cooling
system problems I would avoid pressurizing the system. Coolant is burping out of
the overflow.> When it settles down I see it's down a ways, so I add nearly a
gallon of water.
Most likely there were no cooling system problems.
Oops. I learned from experience, never, ever leave a coolant cap loose on an
OM602.
One of mine had a slow leak (fuel heater) and I left the cap loose, thinking
that avoiding pressure
build up would slow the leak. I severely overheated the engine (wasn't paying
attention)
and smoked the head gasket.
Cracked head?
Not likely. They are very robust.
Bad head gasket?
It probably is now. You will know when you start it. When a five cylinder has a
miss it is distinct.
If in doubt, crack open injector lines one at a time, and see if the idle
drops. (same as pulling plug wire on a gasser)
If it runs on all five, SECURE the coolant cap, and go for another drive.
Good luck, and keep the updates coming.
Rick
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Dan Penoff via Mercedes <mailto:mercedes@okiebenz.com>
May 27, 2016 at 7:13 PMvia Postbox
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Interesting would be a good way to explain my afternoon....
Went over and picked up the 300D. Other than replacing a leaky
injector return line and topping off the coolant before we left, there
wasn't much else to do but fire it up and point it home, a roughly 30
mile trip that is mostly interstate.
No AC, which I knew. Seems like the monovalve must be bad, as the only
thing you could get out of the ACC was heat, and LOTS of it. Fan did
it's thing as I would expect, so the owner's statement about the fan
controller being bad was unfounded. Turning on the AC engages the
compressor and loads the engine, so there's definitely something going
on there. It's still an R12 system, too, which is good. I will have to
get some different hoses for my manifold gauge set if I'm going to
work on it, though.
Car ran great, plenty of power, tracked well and braked well. Very
little smoke on load unless I really put my foot to it.
About 10 miles out, my temperature starts to rise. Hmm. It's up to
110C. Not good. I get to a flat run on the interstate and it comes
back down to around 90C. OK, I was climbing a big hill, so maybe that
spike was from the additional load. Temp begins to increase some more,
now it's up to 100C, maybe 105C. Interesting.
I get off the highway and am now on surface streets. Temp continues to
move up and down until we get to some traffic and now it's about to
hit the red line. I motion to my son who is behind me that I'm heading
for a parking lot on the side of the street.
Pull in, shut down, pop the hood. I had not secured the radiator cap
with the intent that if there were cooling system problems I would
avoid pressurizing the system. Coolant is burping out of the overflow.
When it settles down I see it's down a ways, so I add nearly a gallon
of water. Hmm. This is not good.
We hang out for a few minutes and let the car cool down.
I leave the cap unlatched and we make the dash home with the temp
gauge just tickling the red line on occasion, but not dropping much
below 120C. Ouch.
So here's the deal, folks:
Cracked head? If this were the case, I would expect coolant to be
getting into the combustion chamber(s) and the resulting hydrolock
occurring with the expected result of a bent rod. Not likely, I think.
Bad head gasket? Probably, as this would only be failing under
pressure, meaning that it wouldn't occur unless the engine was
running, preventing coolant from entering the combustion chambers.
Other possibilities? I would have to reach out on this one, as my
experience with diesels isn't deep enough to identify other reasons.
It runs great, has good power, doesn't smoke unless you really put
your foot into it. Nothing remotely indicating an internal problem
that would suggest something catastrophic is going on.
So fellow dieselers, please offer your sage advice as to what
direction I might take on this.
On a positive note, I found the receipt for a transmission rebuild in
2014, and the paint is going to clean up really well.
And yes, I'm ready for my beating. I should have looked for bubbles in
the coolant when I was running it before I took off. I saw a few, but
since it took about 3/4 of a gallon of water I just figured it was due
to bubbles from the system filling up and burping.
Dan
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