Mechanical vs Electrical gauges

[Joe Murray]

I Bought a set of mechanical gauges, oil pressure and water temp. My engine guy says to use electric, because of the oil running in the line, if it breaks or come loose you have oil spraying at 100psi. I heard guys say you can't trust the electrical gauges for accuracy. What are some thoughts on to this and what type/brand of gauges for VW's would you guys recommend
Thanks.

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ahondafor?

[madrabbit15]

mechanical oil pressure gauge is best, use a stainless steel braided line, you wont have a problem with it breaking. When i was on the outside pole at the ARRC last year, the oil line had a leak while sittng on the grid. STU at BSI was there to fix it. Would not have happened if we had had a stainless steel line.

[Bildon]

Electrical are much easier to install and plumb through your firewall. Mechanical have a tendancy to leak exactly where you don't want them to, and must use metal lines which are more difficult to maintain.

However, having said that We can't keep electrical oil pressure senders in one of our cars. Must be the vibration is killing them. Our other car has not seen this problem at all. Both are mounted on the oil filter fitting. But the car which kills the senders has an engine stay rod which may be transmitting vibrations.



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Bill Sulouff - Bildon Motorsport
Volkswagen Racing Equipment
## 2002 ITB NYSRRC Champs ##

[racer_tim]

I have both a mechanical water temp and oil pressure. Steel braided line to the oil gauge, and properlly "grommented" through the firewall.

Mechanical water temp attaches at the flywheel side of the block, near the heater control lines. This was done on the Scirocco that I purchased in 1992, and works fine. I can take some pics if somebody is interested.

Only electrical gauges I have are the tach and the oil temp. I just re-wired the dash for the aftermarket tach, and mounted 2 large red idiot lights for oil pressure and alternator.



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Tim Linerud
San Francisco Region SCCA
#95 GP Wabbit (Bent)
http://linerud.myvnc.com/racing/index.html

[Bill Miller]

I put mechanical oil pres., oil temp., and water temp. gauges in the HProd Rabbit when I re-wired it (also put a mechanical volt meter in as well ). Granted, mechanical gauges are a bit more important in a car that runs a total loss system, but I think the mechanical ones are more accurate. In my IT car, I kept having problems w/ the electric water temp gauge. I tried 3 different gauges, and re-wired all of them, and still got crazy readings. If a mechanical gauge doesn't work, there's not too many things it can be. Due to the problems I had w/ the water temp. gauge in the IT car, I just can't trust electrical gauges.

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MARRS #25 ITB Rabbit GTI (sold) | MARRS #25 HProd Rabbit
SCCA 279608

[Greg Amy]

I have experience in both race cars and small aircraft (I own a Grumman Tiger and do most of the work on it). I am a big fan of electrical versus mechanical gauges.

I agree with the sentiment about accuracy on mechanical gauges; they do tend to be more accurate. However, today's electrical gauges are more than accurate in the rangfe we use them. Hell, I'd even say they're at least as accurate as a mechanical within our needs.

But note that electrical gauges can be calibrated and adjusted (electrically, of course) and when they fail (physically or electrically) they just quit working. Mechanical gauges, however, cannot be calibrated if they're off plus a failure can result in something as simple as a DNF (pressure release, gotta pull out) or as serious as a disaster (fire, engine failure from loss of oil).

Another plus for electrical gauges is that they are easier to install and ultimately lighter (no SS lines, no extra fluids, no mess). Plus, let's face it, you're really looking for trends in your dials; actual discrete numbers are basically useless to the pilot unless you're in the pits and your crew chief wants to know "what the number is." As a driver you're glancing over to see if the needle has moved, you're not looking down to see that the oil temperature is 211.37 degrees. Once you learn the normal range of operation accuracy of the gauge is not important (but consistency and repeatability is).

Finally, on the issue of sensor failures, a simple solution - one that I use in my airplane - is to mount the sensors to a remote block on the firewall, with lines leading from the engine to that mounting block. This resolves the issue of failing sensors due to vibration and eliminates the possibility of flammable fluids in the cabin should a line, sensor, or gauge physically fail.

My Tiger was built with "steam" mechanical gauges for the oil temperature, oil pressure, and fuel pressure, plus a non-shunted ammeter with a big fat wire running through the firewall from the alternator. These items have been the subject of Service Bulletins in regards to failing gauges, chafing and holing delivery lines, and big nasty sparks while in flight. I've talked to many a pilot that got the s**t scared out of them with fuel or oil leaks while at 10,000 feet (which, at a 2000 foot per minute descent, means you're on fire for 5 minutes before being on the ground). I replaced my gauges with an electrical package and plugged all the holes in teh firewall; they've been very accurate and dead-nuts reliable for almost 10 years. Plus, I gained almost 5 pounds of usable load in the process be removing all the lines and fat wires.

I know a lot of folks have an affinity for old steam gauges, but when it comes down to brass tacks it's a failure item that has the pototential to move the issue from inconvenience towards safety.

Greg

[Joe Murray]

Thanks for the input!
I think I'll get a set of electric and sell the mech's. I might be a little gun shy but the thought of oil running around the dash and back out makes me a little nervous.

Anybody on want to buy a set of gauges, includes alumn panel with idiot lights.

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ahondafor?

[Ryan Williams]

I have used both electrical and mechanical gauges in the race Wabbit. With solid motor mounts in the HP (production) car, the electrical units failed after one race due to vibration. I subsequently installed mechanical gauges and they have worked for over two years without failure.

If you use a steel braided line for the oil pressure gauge, you will not have any problems. Regards, Ryan.

[Eric Parham]

In general, I agree that most gauges should now be electrical. But, here's the rub:

In Greg's plane, the object is to land safely no matter what the consequences to the engine. An electrical gauge is less likely to actually "hurt" the airplane's engine (e.g., by leaking oil). If the electrical oil press gauge fails, the pilot crosses more than his fingers and starts looking for a "runway".

On the track, although some may have different priorities, it's not usually worth finishing the race at the known cost of an engine. I've been in two cars (one mine, one not) where the gauge wiring failed making me think I might have just lost oil pressure. The first time it happened (not my car), I pulled in and forfeited the race only to learn that the connector had fallen off! The second time, in my car, I finished the race but became hyper-sensitive to everything else (e.g., oil temp). The third time that I *thought* it was happening, I continued and destroyed my engine (cracked oil cooler flange). Lesson learned!

Conclusion? With an electrical oil press gauge in a race car, you never really know whether to pull in or continue when the needle drops. The best I, for one, can do is guess. But, with a mechanical gauge in a race car, there's never any question (even if it is, in fact, the gauge that caused the problem). You just "shut it down -- FAST".

[Ryan Williams]

The good thing about a mechanical oil pressure gauge is that you can include a low oil pressure switch in the steel braided line to turn on a warning light if the oil pressure drops below a specified value. If the warning light comes on while you are at WOT, you may still have time to turn off the engine before the engine blows. Cheers, Ryan.