How to calibrate oil temp gauge?

Our friend Steve O'Brien has given me some pointers as to where the needle should be depending on the actual oil temperature. He tells me there's a screw in the back of the gauge where it is adjusted, but he's not exactly sure. In my case, the gauge is extremely forgiving and the needle hardly goes up (the gauge does work fine though because the needle goes up immediately when grounding it). How can I adjust this thing? Thanks.

Wonder if the oil sender on the motor is the source of the problem a you have confirmed that the gauge is ok by grounding it and it goes over to pinned reading

Yes Alan, the gauge works perfectly and quickly when I ground the wire against the engine block.

Ricardo:

We must have the same weather as you here in Rhode Islandright now, since my electric gauge seems to be working exactly the same way. I didn't see any adjustment screw on the back of the gauge when I put it in, but didn't look too hard, either.

Too calibrate mine, I just put a magic marker line at 200 F and 215 F on the glass - the only two seetings that were easy to make. Now, with the external cooler it hardly gets over 200 F and I can see it on the electrical gauge but it's way over on the left.

There are two ways to adjust the scale reading if there is NOT an adjustment on the back of the gauge. The first is a sending unit swap-out, but then you won't know what the NEW one will do until it's in (at least it's an easy swap).

The other way is to connect a suitable ohmage resistor in parallel with the sender, sized to put the needle where you want it when "normal". I've been thinking of doing that, but haven't yet had time, so I'll put that at the top of the list for next week and report back.

gn

Ricardo,

The location of the sending unit will have a significant impact on the temperature reading. My first engine came with the sending unit located in the sump. George replaced that unit with a dipstick sending unit. The new engine has the sending unit machined into the case and a second unit in the sump. The temp readings can vary as much as 20 degrees.

Karl

Also be sure not to use Teflon tape on the threads it will produce a false temp reading, this goes for any sender unit.. Alan M

Good tip Alan, I always use teflon tape in plumbing repairs and sure I'd have used it on Speedy, Thanks.

Bruce

Ricardo: I've found that recalibrating your temp gauge is easy.

My temp gauge is probably similar in operation to yours: the gauge needle rises a little less than 1/4 scale (there are no numbers on the gauge) above the little green block on the left hand side when the temp is about 200 F, my usual running temp.

I got out there with an ohmmeter and found this:

At 120 F the sender reads 400 ohms

At 200 F the sender reads 132 ohms

(both of those above are +- 10% for sender quality)

The gauge is basically a voltmeter, reading a voltage through a resistor (the sender) to ground

Gordon ,

Here I am reading into the beginning of the third paragraph and ohm's law ( old ham radio requirments) comes into my thoughts and there it is in your next line ....... I'm impressed ! You taught me something here ....Alan

Wow Gord; that's great! Steve O'Brien told me to adjust the temperature gauge so that the needle is pointing straight up at 180 and 220 is at the 3/4 mark on the gauge. This way if the oil approaches 245 it will also be the red line on the gauge. This, he explained, is considered by most VW engine guys to be the max oil temperature that non synthetic oil will still function without rapid break down and resulting engine problems. I'll need to start tinkering with different values until I get this.

Ricardo: Looks like it shoud be about 240 ohms, but that's a non-standard value. Go for the 220 ohm 1/2 watt - it should work just fine. I looked for an adjustment on the back of my gauge and didn't find any.

Alan:

I received K1FRV when I was 10 years old, later was N1GSN (Navy Mars) and ran THOUSANDS of phone patches out of Vietnam, the Pacific, Germany and the Scientific Expeditions to the South Pole (supported by Quonsett Naval Air Station out of Rhode Island) between 1965 and about 1975, then just never found the time to get back into it. Got several awards from the military for the number of solid phone patches run into the Eastern USA states during Vietnam.

Ran the Hallicrafters twins (HT-44/SX-117 - fantastic audio) and a home brew Linear running three (!) 4-1000's in the final (WAY better than a "Henry 2-K") to a home-brew, 4-element, 20 meter beam cut for 14,305 (the patch frequency) on a Ham-M rotator. I hung a 4' flourescent tube in a tree about 200 yds from the antenna and could see it flickering with the modulation when I talked if the linear was on (oh sure, it was legal........) The linear used to be a ship-board transmitter, donated surplus by the Quonsett guys after the second season of 10-15 patches per night (while I was doing my homework for school!) If we started to get splatter on the patches from a nearby station, a simple slide to their freq, turning up the plate and screen voltage variacs to max and politely asking that they slide a little further off (while pinning their "S" meters) usually worked.

I was also HR3GSN for a while in 1967 out of Northwest Honduras, running all CW four nights a week (Honduras did not require morse for their license) as the ONLY CW operator in HR3 land - what a hoot!! I was also running mobile CW and SSB from my supply truck (Drake TR-4 in there) with a 12V keyer and a vibro-plex electro-key strapped to my leg while driving. While there, I met (a few times) HR1OL, who was the president of Honduras, later deposed for tax fraud and fled the country (sounds like a movie, but it's true).

Ah, the good old days - tube radios and no computers!!

Gordon - a Ham from way back - "Little Brother in New England" for you Vietnam Vets who got phone patches back East.

Hey Gord; Thanks so much for the tip; I'll definitely use it! I'm sort of a tube nut too; I'm a guitar player and all of my amps are tube (old technology but until now the best sound, at least for electric guitars).

You just can't beat tubes for audio amps - Good tube versions have absolutely no leak-through hiss (so inherent in transistors) and the hum from the heaters can be easily eliminated to give the purest sound you can find. Look how organ players love the "old" Hammond B-3's while there are so many good synthesizers around these days. Hammonds just sound GOOD! Same thing for the tube guitar amps - for purity of sound and no residual hiss, you can't beat tubes.
There are a few good transistor amps out there (many, really, FET systems that more closely mimic the action of tubes) but they're wicked expensive, as I understand it, and FAR more costly than tube types.

Mi dos centavos........gn

I thought tubes were all but extinct but as of late, Groove Tubes out of Ca. has opened a new US tube production facility. Would you believe that? I don't know how they can do it; with all the recent EPA regulations (as you know there's a lot of toxic by-product in the manufacture of tubes).

Gord; finally, with the help of JJR (an EE too) we followed your advice and although working better (obviously our resistance values varied a little from yours being different gauges) we find that basically what we do is drive up the effective range of the gauge. Still, though, when the engine is cold the gauge shows up slightly higher than the first little square. How can we tweak this thing so that when cold the needle is at the bottom?....Thanks!

I can tell you, with resistors in parallel you wont get to what you want, you will have to replace the sending unit. Wouldnt it be nice if you knew the new units ohmiage range beforhand?
Disc brakes are here, they didnt send the brake pad, there goes my crusin sunny Sunday... BCNU

Unfortunately, JJ's right. Adding another resistor in parallel will simply move the needle range up the scale for any given sender.

I guess I lucked out - I played with several values before I settled on a 220 ohm resistor in parallel with mine, the needle is about on the bottom line when cold, and when running 200 degrees it reads about 1/3 scale or there-abouts.

You might try running a slightly lower resistance value, like 180 ohms or so, or, as JJ said, just get another sender and see what happens........I had another sender on hand (for a real 356, actually) and it made it worse, so I opted for the cheaper and faster "added resistor" route.

gn

Know what Gord? What Alan and Karl say makes sense. I need to verify this but I think the sender has some Teflon tape around the threads; that might be throwing it out of whack...I'll check and report back.

Yup! Also consider adding a ground wire from the back of the meter to a grounded point. Its not complicated and might help...

We'll do that JJ...also wanted to add that after tweaking the oil temp gauge, now the gas gauge is working properly. It used to show half full when full. I don't know if one gauge is affected by the other by being on the same unit.