Coolant Pressure Control Cap

[Leroy Eckert]

Your theory may be totally correct.

My understand of cap pressure values, the higher the pressure, the higher the
boiling point. Assuming BB used top quality hoses and I believe they did I have
some trouble differentiating between the bus and my Cummins SLT 3/4 ton PU, when
it comes to cap pressure. My diesel truck heating system is tied to the cooling
system and it has a factory 15psi cap. My bus has a 13psi cap that I did not
install and over the past 3 years all has been good. The DD service manual says
7-9 psi. I give up, maybe.

Over the past few months I have been making small changes to the cooling system
in my bus. I am taking chances, testing them on my bus, in an effort to reduce
overall temperatures in the engine, transmission, retarder and engine oil. I
have changed the Alarmstat, which operates the hydraulic fan to 190 degrees from
195 degrees.
I will not know the full extent this change until summer, but so far it is
working.

Before I decided to make the change I consulted with DD approved shops and BB.
I was not satisfied with the answers sooooo, I pressed on.

The DD manual says to be careful not to have cooling system components operate
out of sequence because the result will be overheating. At this point in my
testing I have concluded the foregoing to mean, the cooling fan, the engine
thermostats, and the alarmstat, primarily because I do not know of any other
cooling affected components other than the cap.

Before I embarked upon my mission, I was told that temperature cycling was the
result of the engine thermostats cycling. Unfortunately, I cannot force that to
happen and I have tried. I have driven the coach in temperatures of below 32
degrees with the fan override on and my water temperature gauge stabilizes at
about 170 degrees, the engine thermostat value. In other words, it doesn't move
once stabilized, so the engine thermostats are not cycling(possibly). If they
are it is happening so quickly that it does not register on the temp guage or
they partially close and shut down the water flow to hold the constant
temperature. I cannot see them work. When I turn the fan override off the
temperature begins to cycle off the Alarmstat between 180-190 degrees.

All of this fits the DD published coolant Series 92 publication in my
possession. Why BB dedided on a 195 degree Alarmstat, only BB knows and they
aren't talking, because I have asked. I simply does not make sense to force the
temperatures to the outer limit of DD specifications, ;and that is what happens
in summer. Heat is our enemy and I have been able to reduce the heat.

Most likely, I will change my cap to 9psi sometime in the summer and see if that
makes any difference. My guess is it will not simply because keeping the engine
cooling system within temperature specifications precludes any real need for the
cap to blow off.

I like my drive train component temps now.

Engine Oil-215
Water Temp-Cycles between 180-190
Transmission Temp- 170
Retarder Temp- 220
All recorded in flat conditions at cruise speed of 68 mph, pulling a 20ft
trailer w/car.

I do not suggest you try anything unless you fully understand your system, I'm
simply reporting what I did.
The foregoing presumes that all system components are in proper working order.

My next project is to install MH's water injection system so when I climb the
mountains next summer I'll have a water flood just in case.

Alright, fire away, I have Redneck engineering paperwork on this one. LOL lol,
lol

Leroy Eckert
1990 WB-40"Smoke N Mirrors"
Niceville, FL



----- Original Message -----
From: Fred Hulse
To: WanderlodgeForum@yahoogroups.com
Sent: Sunday, March 04, 2007 11:44 AM
Subject: Re: [WanderlodgeForum] Coolant Pressure Control Cap


My theory about the 7 lb. cap is the coach heating system is tied into the
cooling system and Blue Bird has used that pressure to protect the other systems
in the coach,let alone miles of heater hose!
Fred & Jeanne Hulse
Morristown Arizona
1997 Wanderlodge WLWB41

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