Temp range for coolant guage on 83+ Vanagon/Westy - results

[Lanval]

Hi guys, (82 Vanagon/Westy manual 4-spd - stock Air-Cooled)

I installed an '87 vanagon cluster in my Westy, 'cause I wanted to spiffy lil' tachometer so I could tell when I was about to blow a gasket.

Now, the coolant gauge is a fine little gauge, and I got to wondering what temperature range it's set up to read/display? Would it be possible to get an oil temp sender for the drain plug and run it up to the coolant gauge? Or another sender, for that matter?

Or did the coolant gauge use a special kind of sender?

Just wondering heh, heh.

Lanval

[MarkWard]

I believe it is the same sender or similar. 049 919 563 A
Is a small oil temp sender. You won't know that actual values unless you can compare them against a gauge, but it should at least give you a normal engine value and let you know when something is amiss. Good thinking. The sender is just a variable resistance sensor to ground.

[bucko]

O.K. oh wise one TENCENTLIFE....

What do you have to offer on this idea? I like it for the air cooled side. Sounds like something can be done.....
_________________
Current VW drives: 1984 Westfalia

Past VW drives: 1967 Beetle, 1973 Beetle, 1977 Bus, 1971 Military Type 181

[Lanval]

Yeah, we need the dime. I'm assuming it would work on the theory that in my volvo, the coolant temp and oil temp are basically the same (180-210 running) so that a temp sender which functions in the 150C/300F range would probably work on the coolant gauge.

If that's the case, it's true that the scale isn't exactly precision, since it's location based, but hey, if that's good enough for the coolant, why isn't it good enough for the oil... I just wanna know if I'm in trouble or not, and for that a daily reading in an approximate range is enough.

Where O where is the Samban Oracle?

Bump for an answer.

Best,

Lanval

[tencentlife]

Oracle shmoracle snorkel yer dorkel. rsxsr is dead-on, a temp sender is a just a variable resistor to ground. It's actually called a "thermistor" in electronic-nerdspeak (I'm not one, nor do I play one on TV. It's behind the camera only for me). If they operate in NTC (Negative Temp Coefficient) mode and their range of resistance is the same, one is as good as another. You could even match a gauge to a PTC resistor and invert the gauge representation if you wanted to measure coolness, for instance.

I've described somewhere else, or probably more than once, patient soul that I am, how a mechano-electrical gauge works, where the sensor completes the circuit to ground thru the gauge's coil and by varying resistance it varies the field strength that moves the needle against a spring counterforce. A thermistor has the unique property of decreasing resistance with rising temp, unlike normal resistors that do the opposite.

If you have a thermistor that works in the same range of resistance as the one intended for the gauge, it will supply a similar resistance at a similar temp, and so cause a similar needle deflection. So it doesn't matter what substance you're measuring the temp of; if the sensor is physically compatible with the substance (oil, water, surface temp of a metal, acid, whatever), the same temp will read the same on the gauge. OEM water gauge scales are obviously arbitrary, so "normal" is where they say it is, but you'd get the same range of movement in the same range of temp, and it's up to you to know what normal is. You can just as well heat or cool the thermistor you wish to use to certain measured temps and mark the gauge scale at each, and that way you can impose absolute values on an arbitrary device.

[Lanval]

Tencentlife,

At first I was chapped, 'cause you didn't answer my question. What I wanted was the statement "the wasserboxer sender measures in the range from 0-200C or 0-150C" - which is not what you said.

But you're answer, if I read you right, is that it really doesn't matter - any sender which functions on the same principle will work, and the gauge will read wherever it reads - BUT, that reading will be constant assuming the engine is constant, so that as long as you have a known good point, you simply mark the deviation from that standard point (be it high, low or middle of the gauge), and decide whether it constitutes acceptable or not.

OK, I'm with you there; but I was wondering if we could just scale the sender to the gauge. If you go over here: http://www.egauges.com/vdo_sgrp.asp?Subgroup=Temperature_Sender
you can see that VDO offers senders in three range options:

120C/250F
150C/300F
200C/400F

If we knew what the original sender was, we could then use the (approximately) correct range to get a gauge that didn't look funny/wrong.

The Bentley gets me pretty close; here's the info it gives:

"Thermostat
opening begins: approximately 85C/185F
Opening ends : approximately 105C/221F (pg. 19.

and later,

"Thermo-switch for fan - thru 1985
Cut in temp: 93-98C / 99C-105C
199-208F / 210-221F

Cut out temp: 88-93C / 91-97C
190-199F / 196-206F"
(Bentley, 1991: pg. 19.12)

In general this suggest to me that a 150F/300C sender is appropriate, since these are fairly close to the numbers I see for my water cooled Volvo. So I suspect that the gauge was originally meant for this range; BUT - I'm actually driving an air-cooled, which I've been told runs quite a bit hotter than the water cooled. Thus, I'm wondering if a 200C/400F sender would keep the needle lower, and thus more useful.

It seems to me that if I use the 150/300 sender, and the engine is always at or around 300, then the needle will always be pegged, or nearly so. That number seems high to me for ANY oil, regardless of weight, but I don't know, which is why I now ask a more intelligent/thought out version of my original question:

Is the oil temperature range on an air-cooled vanagon similiar to the water temperature range on a water-cooled vanagon. If not, what is the appropriate range for oil temps, so that I can get a sender which will offer a wide enough range to accomodate the oil temps.

Thanks all,

Lanval

[tencentlife]

Yeah, you're on it. When you look at the VDO gauges and senders, for instance, you want to match a 300F gauge with a 300F sender, because that means that at 300F the sender will have the correct low resistance to put the gauge needle at the 300 mark. The wrong sender might offer a similar resistance at a lower temp, for instance, so in that case the gauge would end up reading too high.

What the exact ohms are at a given temp may be proprietary info, but it's easy to find out by heating the sender to some known temps and noting the resistance. By taking two or more temp readings, you could calculate the temp-to-resistance relationship, and express it as a coefficient of temp, e.g. -20ohm/deg.C, or something like that. The coefficients may be linear, which would mean you could determine the coefficient with only two measurements, or logarithmic, which would require more measurements and involve math that is over my head since I got out of the tenth grade. I don't know that much about it, but you'd find out pretty quick if you set up the tests. Take a look at the tables in Bentley for the engine temp sensors and you'll see their coefficient expressed as a graph. Those appear to be logarithmic.

If you know the coefficient for one sender, you could pick up a sender of a different make or unknown application, and make the same measurements and know if it would work.

Your question seems to be, are the normal working temps of water and oil nearly alike in a water-cooled engine, and is the oil temp of a water-cooled engine nearly the same as an air-cooled. You already know the answers to those questions. Water temps will usually run in the 180-220F range, give or take ten degrees, and oil temps need to work in the same range regardless of cooling system type, about 180-220F. Huh. The ideal ranges are about the same. Wow, that means that the same gauges and senders will work for either, provided the senders are physically allright being immersed in the fluids in question. Aircooleds have to keep oil within the same working temp range; they use the same type of oil, and viscosity breakdown occurs at the same high temps for given type of lubricant. It's head temps on aircooleds that are in a different range, more like 300-400F. But the oil in the bottom end is still going to start losing its lubricating properties if it gets up over 230F or so; whether the top end gives its heat up to air or water doesn't matter.

So, yeah, I'd say you already worked out the answer for yourself.

[Lanval]

Yeah, TenCent, but I learned from the best. I'm thinking about changing my nick to 'Nickel' - 'cause I wanna be a dime someday -

Thanks for confirmation, I'm going to try the sender and see how it works. If it's no go on the dash gauge, I'll just hook up a regular VDO temp gauge, and mount it next to the two voltmeterts that'll be going in

Thanks again,

Lanval

[tencentlife]

Did you mean TWO voltmeters?!! Why two? Are you monitoring your aux battery too? You know, you can have one meter and switch between different sources. That's what I want to do. But I want a rectangular LED surface-mount VM, because mounting positions for round gauges are so few. I want to put it up high, so it can be read from the back and I can see how the aux battery is doing when I'm camping. LED meters are hard to find, though.

What's your plan? What gauges are you using?

[Lanval]

No, I meant voltmetert - these are evil wizard meters that seek to destroy boy-wizard meters. Hmmm. That joke was funnier in concept than in practice. Da*%$#it!

Yeah, my plan is to do the triple mount with two voltmeters and an oil temp. The oil pressure is too much work to fit.

I will run a secondary battery to power the westy stuff + computer/DVD player, etc. I bought a couple of VW trickle chargers, so once I get the 2nd battery in, I can run another 12 volt outlet in back by the bed, and trickle charge both batteries while camping etc.

I just use the old round analog gauges which come out of the VW rabbits. I have one full set (Volt, pressure, temp) plus some extras. The voltmeters are really the valuable ones, to me, because the voltmeter is the only one I've ever really used in my Volvo.

I haven't quite decided where I'll mount the gauges. The most likely places are a dual mount for the primary battery and oil temp up front. Those are driving gauges.

I don't remember who I saw do it, Mighty Art or MS in a Bottle (shout out to Winston - travel the roads in safety my friend!) but the mount placed next to the shelf above the cooking unit looked good for the aux battery. I might mount it in the cabinet, but am loath to cut into a perfectly good westy.

I'm still waiting for the Van to come back from the shop - my guys are good and cheap, but they're trying to round up various parts from used sources, to keep my cost down. Brad at Nyscoe Motors in Santa Ana, CA is the THE choice for work on Air-Cooled VWs.

So all my talk is hypothetical planning.

Are you gonna make your own LED gauges? I know guys in the Volvo forum who do that from stuff bought at Radio Shack. It's a pretty simple structure, and I can dig up the info, if you're interested.

Any reason for LED vs. mechanical? I use the old gauges 'cause they're $5 a pop at the junkyard, and pretty plentiful - more about availability and simplicity of use than anything else. Just wondering if LED is a better option...?

Thanks TenCent,

Best,

Lanval

[tencentlife]

I want an LED gauge for my rig for several reasons:

Low power usage means it can just stay on all the time.

I've already used the space in the lower dash panel (heater cover) for two round gauges, OP and OT, and there isn't room for more, and I want it up high anyway so it's easy to read from the back cabin while we're camping.

I have a $5 junkyard-special voltmeter, but I want a digital meter for the cabin battery. Analog voltmeters are OK for relative comparisons while running to verify charging, but for working off a static battery supply, there's a big difference in available energy with every tenth of a volt. Automotive analogs just don't resolve to a tenth. Plus I'm used to digital readouts on my home battery. I'm not into building my own, not worth the time, but in a straight-up 12V-powered version, LED meters are kinda hard to find.

My rig is just a plain 7-pass but we use it for camping. It has the overhead AC ducting, so a small rectangular surface-mount LED gauge would fit nicely up on the eyebrow console, next to one of the AC switches, and I could see it from the back or even from outside the van if I want to check the cabin battery. I would use a little toggle switch next to it so I could check the voltage of either battery with one gauge. That's actually overkill, since when the engine is running, both batteries get combined and their voltage should be about the same. Under charge, absolute values aren't as important as relative values, but when we're parked and running off the cabin battery, absolute values are what I want to know.

Why is OP so much trouble to fit? If I could only have a single instrument in a car, I would want to know OP. If you're concerned about where to add a sender and keep the pressure switch at the motor, you can come off the pressure switch port on the motor with a tube, and mount as many pressure sensors as you want in a manifold wherever you like. Like this:

The tubing takes off from the stock oil switch hole on the side of the motor:

I know yours is a T4, so the switch is on the oil cooler bracket, but the concept is the same. Pressure within a containment with a static fluid is exactly equal at every point in the vessel, only varying due to elevation, which in this case is insignificant. There is no flow thru the tube to create any variation, so all the senders are seeing the same pressure.

By the way, if you decide to do OP after all, stay away from the combined OP senders that have a gauge ground and an idiot light switch. They aren't as reliable as the stand-alone sender and a separate idiot light switch.

[Lanval]

Thought I'd bring this back for an answer round - this kind of stuff works best if we find out how things went, no?

So I got a taco plate sender set up from Scott at German supply, was installed with some other work. I wired into the temperature gauge position on my post-85 cluster, but could not get a reading.

The gauge itself appears to be functioning normally, in that it goes through it's check routine on startup (lights, flashing, etc.), so I don't think the gauge is bad, though it could be.

I installed a VDO oil temp gauge, using the same input line, and got a reading of 110 deg. Cel. at idle (didn't drive around, just sat in the parking lot). That seems about right, maybe a bit on the high side, but OK for idle probably.

This leads me to think that although the senders for water and oil temp function in the same range, that the VW coolant temp sender had a different signal range or something. Anyway, it'll take someone with more electrical knowledge than I have to figure it out, but just as a seat of the pants test, it didn't work.

Thanks for your input TenCentLife - over the winter I want to put in an oil pressure sender, 'cause I've got a gauge for it. Gauge shows lb/in, though... that's a first for me.

Best,

Lanval

[tencentlife]

Did you do the basic function test on your new gauge. That is, power up the gauge, and take the end of the sender wire and ground it out. The gauge needle should shoot to the top of the scale (maximum current flow thru the wire with no resistance to ground causes the maximum field strength in the gauge coil, which lifts the needle the furthest against the calibrated spring counterforce). The unground the sender wire, the gauge should read at the bottom of the scale. If that test works out, the gauge head has power, and continuity to ground via the sender wire. So that means the gauge is OK, the problem is in the sender.

You can then test the sender at cold and hot temps by putting it in the freezer and in hot water, and checking the resistance between the wire connector and the body of the sender. It should have high ohms when cold, and much less when hot. I think you should do those tests because there isn't any reason I can think of why what you are trying wouldn't work.

Another thing I just thought of, is that your late gauge works with the coolant level warning system as originally installed, but you don't have that system in your aircooled rig. So that could be a factor. I thought the flashing LED was controlled by the level warning relay. I would have to look at the diagram to see if the gauge would work on its own, and my book is far away right now. But do the basic test, and take a look at the schematic and see if you can figure that out.
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[Lanval]

Dime, I'll check that when I get a chance (it's gonna be a few days ~ I saw my advisor the other day and she said, "why don't you go read 15-20 books and come back and see me in a few weeks"... ouch.), but the sender does seem to work OK. We're going to the beach today, so I'll have a chance to test the VDO oil temp gauge under load. I'm a little suspect on the gauge, so I actually want to check and see what the sender is doing.

I'll go back to the schematics for the water-cooled and see if I can figure out the circuit. It may be possible to rig up a solution if the issue is merely an open circuit.

Thanks again,

Lanval

[Lanval]

So I swapped out the questionable gauge with another one. The reason I suspected the gauge was that when wiring it in, I hooked it up to the tachometer line first. This results in gauge death in Volvos, so I figured that would be the case here.

After hooking up the gauge and driving to the beach and back (25 minutes, some short steep hills), the engine oil temp was running between 105-110 Celsius, measured at the sump, when fully hot.

When I get a chance, I'll check the signal coming from the oil temp sender, and then look at the wiring for the coolant to see if there's a way to set this up.

Just as an aside, how does that temp look? It's a little higher than my old Volvo 240, but I suspect the engine simply runs hotter ~ 105 C = 221 F; 110 C = 230 F.

This seems a bit high to me.

Best,

Lanval

[tencentlife]

That's OK for oil temp. I'm comfortable so long as it's below 230F. That's not causing damage to the oil at that temp. Above 230 seems to be where viscosity drops off the cliff, and pressure with it.
_________________
Shop for unique Vanagon accessories at the Vanistan shop:
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Please don't PM here, I will not reply.

Experience is kryptonite to doctrine.