Date: Mon, 12 Aug 2002 06:07:05 -0700
Reply-To: TinkerMan <tinkerman007@YAHOO.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: TinkerMan <tinkerman007@YAHOO.COM>
Subject: # Importance of pressure and temp monitoring (long)
Content-Type: text/plain; charset=us-ascii
Hi Volks!
Recently, I had the radiator fan speed reduction
resistor go down on me. As a result, the radiator fan
would turn on only at high speed when the coolant was
really hot.
I didn't pay attention in the beginning, thinking it
was the hot weather...
Well, in the end, this resulted in a blown A/C dryer
pressure relief (requiring replacement of dryer and
refrigerant, $$$$$) as well as a blown coolant hose.
The A/C pressure relief blew because my A/C serviceman
hacked a replacement pressure switch which somehow
didn't protect the A/C system from high pressure.
Why high pressure? because the radiator fan didn't
cool the radiator most of the time, until coolant was
really hot (the resistor burned in the common circuit
that controls both the low speed as well as the A/C
minimal speed activated when A/C is on). In the end,
that was enough to cause exessively high pressures in
the A/C to blow the pressure relief valve.
And why did the collant hose blow? because the higher
engine coolant temperature resulted in higher
pressure. Of course the coolant pressure cap should
have relieved it (and might have if it reached 15psi),
but old hoses always are a weaker point in the
system...
Still have to check the coolant pressure release cap
for 15psi, although it was lately testy OK. Darn,
can't rely on those dealer mechanics (BTDT...).
Also, there have been many posts regarding engine oil
pressure monitoring. Many say that catastrophic
failures can be avoided if unordinary pressures (both
low and high) are noticed. Even the builtin so-called
"dynamic pressure monitoring system" isn't enough and
won't detect exessive pressure instances at all (e.g.
when pressure relief valve is stuck).
Which leads me to the obvious conclusion that all
pressures of important systems must be monitored and
warned against exessive pressures: Oil, coolant, A/C,
etc.
I know this sounds paranoid but from my experience
noticing a simple failure promptly and taking action
can save huge sum$ and grief resulting from
catastrophic failures which could have been avoided.
SSSOOO...here's what I'm looking for:
1. Good point to check coolant pressure. Methinks that
a convenient spot would be the "T" where the left head
connects via hose (VW 025-121-058M) to the coolant
manifold. A "T" could be added for the sensor without
changing the system. Any better spot, e.g. the coolant
distributor, outputs to the rear heater which I don't
have? I don't want to drill a hole in the coolant
expansion tank like someone suggested...(I've had
enough trouble with that one!...).
2. Good spot to measure oil pressure: Many have
recommended the 0.3 bar pressure switch location with
extension hose and dual sender or "T" with standard
sender: Is this BEFORE or AFTER the oil filter?
Anyway, I don't like this extra hose dangling around
there (even tied to something) but maybe there's no
better option. Any better ideas?
And I want to connect to it THREE senders: the
original 0.3bar, an analog sender and a high pressure
alert (in case of overpressure). Anyone know what
would be the maximal recommended oil pressure? What's
the spec of the oil pressure relief valve?
3. Good spot to measure A/C pressure: wouldn't be easy
(no place to tap in). Maybe use the integral pressure
switches with a buzzer, but have to make sure the
sender is working OK first.
******
After we finished with the pressure issue, now comes
the temp issue...
1. Coolant temp is monitored in the dashbord, but is
quite unreliable: I had a double failure where my
coolant leaked overnight, and my coolant level sensor
(in the expansion tank) was cracked and allowed
coolant to seep up to the connector, so when I drove
happily away my dashboard meter showed nothing (temp
sender was measuring air temp in the thermostat...)
and the coolant level sensor indicated all was well
(because the wire connnector above was wet, fooling
the coolant level "relay" to think there was enough
coolant...:-(
Well, since then, I've added a seperate sensor right
on the #3 head (hottest?) near the coolant exit
(there's a threaded standoff there) and it works
great. I even have an alarm circuit that can be set to
a certain threshold, both for coolant temp as well as
head temp (near the coolant exit). I thought about
even adding another sensor at the exhaust port
(another threaded standoff there) but I'm not sure if
my sensor will stand those high temps.
Anyone have a wide range thermoprobe to measure what
temps can be expected there?
I'm just wondering where is the best place to sense a
catastrophic failure (coolant or oil loss) resulting
in overheating. This is more relevant in aircooled
engines, but can be used to the benefit of W.C. too.
Anyone know what's the best place to measure temp on
A.C.? Maybe there's a similar location on WC since the
engines are based on the AC design?
2. Measuring oil temp: I'm aware of the various
methods of measuring this (drilling sump plate and
installing sender, but prefer not to drill, or temp
sender dipstick which is claimed not to be accurate).
All in all, I think I've got it covered with my other
temp sensors.
3. I need a source for LOW COST but reliable senders
for the above. VDO might be good, but are defenitely
not cheap. Also, ideas for tapping into the various
systems to be monitored.
4. The most important issue: with all those sensors
and senders, I need to display them all...
I don't have room (or desire) for an airplane cockpit
in the dash, so I'd like to have a single meter there
switchable to the various senders. The problem is that
usually each sender has it's own characteristics and
matching gauge. I'll have to scale them down for a
single compact meter, hoping they all are referencde
to ground...
Well, that's my rambling. If anyone has implemented
such monitoring stuff, I'd be glad to hear practical
experiences and recommendations...
=====
Cheers, T-man.
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