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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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