Gauges, Temperature, Pressure, OH MY!
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Author:  pyrOman [ Tue Jun 23, 2009 7:39 am ]
Post subject:  Gauges, Temperature, Pressure, OH MY!

Since my early days driving and working on these aircooled engines I often wondered what is "normal" operating conditions as it relates to temperatures and pressures. We all pretty much know that the oil light comes on around 10psi or less and that 180F for oil is considered the norm. But I have gotten no answers when I asked even engine builders what is a good running temp for the head? :???:

Well, in my experience now I've determined that head temps below 350F is okay but would rather keep it below 300F just to be on the safe side. I've also melted a spark plug at 450F so I know NOT to go there! :shock:

Some of us, after driving these vehicles for so long will learn to "feel" when the engine is not operating properly, i.e. running hot, loosing power, not getting enogh gas, flooding, etc. But others rather have the advantage of using gauges to better keep up with what's happening "out back". :smile:

I too like the use of gauges but have come to find that some times even new gauges and sending units are bad and will give false readings. This can be detrimental in either case as it could damage an engine that you thought was running okay or prenvent you from enjoying your drive beliving there's a problem where non really exists. :sad:

For these reasons I verify my gauges and sending units against calibrated gauges before installing them, even if they are new! I've found out that some senders indicate low pressure by keeping the oil light on when it really is over 20psi. Also gauges that don't read anything until the true pressure goes over 30psi, and others that are just extremely off in their reading! :-o

Recently I decided to crack open bad sender just to see how it works. From what I found, I believe I can get it to work correctly and reseal it for use again! :cool:


No more mystery! This side shows the light switch.

This side shows the gauge potentiometer.

It looks dirty but dry, as in no oil has leaked to the mechanism so I'm sure a little cleaning, adjustment and reseal will get this sender working correctly again! If successful, I think I'll start collecting bad senders for repair. Maybe pick up the slogan "All your senders are belong to us!" :lol:

Author:  BONZIGH70 [ Tue Jun 23, 2009 4:11 pm ]
Post subject: 

That's very interesting. I knew pretty well with my old bus good noise bad noise and could feel when something wasn't right or if it started to get hot. Today going to work I lost all power all of sudden. I started to freak Oh my God Ive blown an engine but then I noticed no red light so I calmly got the bus off the freeway and to work. After I parked it I checked everything turned it on and listened but paranoid that something horrible had happened to my engine I started to hear all sort of bad noises so I said screw it and let the mechanic look at it turns out my points failed and the carb was off slightly. I always thought gauges would be a really cool thing to have but I know people who just get fixated on them if the needle moves in anyone direction they just start to worry usually needlessly. That could make you really nuts though with a faulty sender.

Author:  auslander [ Wed Jun 24, 2009 7:14 am ]
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Picked up a full set of gauges cheap at OCTO, unfortuneatly no senders. I got a cylinder head temp, tach, oil temp, oil pressure, and voltometer. I ordered all the senders and already got them in the mail. Went by wiring works and had them make a wiring harness for the cht. I've never had any aftermarket gauges of any type so this will be a learning expierience for me.

Author:  pyrOman [ Fri Jun 26, 2009 12:32 pm ]
Post subject: 

Alright, managed to make one good sender out of 2. The one pictured above had a burnt light switch contact whereas the other one had a seriously burnt/melted pot. That's why it would not read until it reached the "clear" area of the pot. :roll:

So I swapped parts, soldered new wires and checked the calibration on it.

Before adjustment:

After adjusment:

I had a gauge ready for the bug with the bezel in grey instead of black, which was an 80psi dial rather than 70psi. Once I tested it, I realized the sender was closer to it than to the 70psi one. Also, found an "error" throughout between 2 to 5 psi. So I dialed it in to be within 1psi at the lower end which is the critical area. So at 10psi it is right at 10psi! Then set the light to trigger at just under 7psi. Specifically at 6.86psi but who's counting! :razz:

Anyway, now I'll need to seal it with some silly-cone and solder the wires at the end of the threaded terminals and it'll be good to go! :cool:

Author:  auslander [ Tue Aug 30, 2011 8:50 am ]
Post subject:  Re: Gauges, Temperature, Pressure, OH MY!

What is the correct name for the connectors on the VDO CHT gauge setup, not the thermo coupler but the other end???

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