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Topic: radiator cap for rear radiator 6v92? (Read 551 times) previous topic - next topic

radiator cap for rear radiator 6v92?

What should be used 15 lb or less?
Ken & Peggy
91 GV  U300 40'
DD 6v92
Build #3819
2023 Canyon Denali 4x4 crew cab

Re: radiator cap for rear radiator 6v92?

Reply #1 –
That is what our '93 has. Check your soldered tube that goes over to the plastic tank. Ours came loose, leaked and I soldered it again. Your black tank may be in a different location with the rear radiator or is yours a late '91?

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: radiator cap for rear radiator 6v92?

Reply #2 –
Early 91 no black tank. Over flow tube looks good. Thanks for info
Ken & Peggy
91 GV  U300 40'
DD 6v92
Build #3819
2023 Canyon Denali 4x4 crew cab

Re: radiator cap for rear radiator 6v92?

Reply #3 –
I can't find the spec right now but I'm pretty sure Detroit says  7-9 PSI cap to prevent damage to O rings between head and block.  There was a discussion about this on the WOG board with the DD spec but I can't find it now. I think my 1985 and my 1982 6V92s had 7# and 9# respectively.

TOM
SOB (Some Other Brand) division
1995 Wanderlodge WB40
8V92 :D

Re: radiator cap for rear radiator 6v92?

Reply #4 –
If the 7 pound works and engine does not overheat use it.
96 U270 BUILD 4810
85 380SL
Drummonds TN.

Re: radiator cap for rear radiator 6v92?

Reply #5 –
I checked with a factory Detroit site that recommends a 9 PSI cap. In reading posts, some have 7 PSI caps, others 14 PSI. Several had problems using the lower pressure cap with rapid loss of coolant so went to the 14 PSI cap, the same as ours.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: radiator cap for rear radiator 6v92?

Reply #6 –
From the little research I just did:

50/50 coolant boils at 223* F.

For every 1 PSI increase (radiator cap) the boiling point goes up 3*F

So, a 7 PSI radiator cap would have a boiling point of 223 + 21= 244*F

9 PSI radiator cap would have a boiling point of 223 + 27= 250*F
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: radiator cap for rear radiator 6v92?

Reply #7 –
I see Cummins owners run between 8# and 15#. Owners say the plastic tank found on some fails at 15#. Most all Cummins have wet liners/O rings with the exception of the 5.9 and some CATs.

Pierce

Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: radiator cap for rear radiator 6v92?

Reply #8 –
Quote from: wolfe10 –
From the little research I just did:

50/50 coolant boils at 223* F.

For every 1 PSI increase (radiator cap) the boiling point goes up 3*F

So, a 7 PSI radiator cap would have a boiling point of 223 + 21= 244*F

9 PSI radiator cap would have a boiling point of 223 + 27= 250*F

I would not be happy with my 8V92  at 244 OR 250! 

TOM
SOB (Some Other Brand) division
1995 Wanderlodge WB40
8V92 :D

Re: radiator cap for rear radiator 6v92?

Reply #9 –
Quote from: OldManSax –
I would not be happy with my 8V92  at 244 OR 250! 

TOM

True, BUT.............

While those coolant temperatures on your gauge would be way too high, your coolant temperature in small areas next to the cylinders will likely be well above your "average" or temp sensor reading.

And, if the boiling point is exceeded anywhere, the conversion from liquid to vapor will force coolant out the closed system either into an overflow reservoir or onto the ground.  Could certainly give you a false feeling of "loosing coolant".

I would go with the radiator cap speced by your engine manufacturer for your engine serial number.  No need to "reinvent the wheel" here.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: radiator cap for rear radiator 6v92?

Reply #10 –
Quote from: OldManSax –
I would not be happy with my 8V92  at 244 OR 250! 
TOM
I don't think many would be happy with those temps in any coach.

But, pressure caps with a boiling point of 244° or 250° give protection in the coolant passages around the exhaust valves in the cylinder head where they are much higher than the temperatures you see on the gauge. If the coolant boils in these passages, it creates a void or area without any coolant to conduct heat away from the critical valve seat and stem area. The damage done here to the valve seat inserts, valves, head gaskets, etc., may not be immediate but can be cumulative  rearing it's ugly head thousands of miles later

So, when I see the gauge hit the 200° mark on the gauge, I know it's much higher than that in the critical engine areas so I back off the throttle, shift down or any combination of ways to keep the temp stable. This also includes turning on the heater in extreme cases.

Marginal cooling may not show itself in all seasons but with higher ambient temp, high density altitude and unfamiliar topography, you can suddenly find your engine temperature has gone into a narrow caution range.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: radiator cap for rear radiator 6v92?

Reply #11 –
And all of this is an advantage for parent bore engines like the 5.9 Cummins and the 3208 CAT as they don't have liners and no O rings to be damaged. Overheating will still cause problems but just not with the liners/O rings.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: radiator cap for rear radiator 6v92?

Reply #12 –
So in reading it seems a catch 22. If you use 9 lb cap it may allow to high a temp for valves, but a 15 lb cap to much for o-rings. It seems that members with dd's seem to use a 15lb cap. I assume this is because of the poor cooling of rear radiator and or side mounted.
Ken & Peggy
91 GV  U300 40'
DD 6v92
Build #3819
2023 Canyon Denali 4x4 crew cab

Re: radiator cap for rear radiator 6v92?

Reply #13 –
I've got great 3 season cooling. Summers are not so good. It's not only Detroits but even. some of the U225 have had the trouble. Some forum members have installed a small radiator up front in the smaller coaches I have never heard the story about the O rings. All wet sleeve Diesels have O rings. The 2 cycle Detoits only have 2 inches of sleeve exposed to the coolant. I never let ours climb above 200°. I don't think you can assume that 9 is OK but roasts the valves but 15 floods the crankcase with coolant. I have 15# but have never had any O ring problems. Quite a few Cummins have 15# caps. Lot's of wives tales start this way.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)