Electrical vs. mechanical gauges

With very low expectations and more than a little curiosity, I bought a kitschy 80s LED bar-graph multi-gauge for my Saab C900 project. It looks suitably period for the car, but (unsurprisingly) it doesn't work very well. It's not staying. But I do want gauges, which will be of a more conventional type. I've already put too much money into an ostensibly cheap project, so expensive options are out. A triple gauge set is very likely the way this is going. This leaves me with two basic set of options: electrical gauges or mechanical ones.

I've always used electrical gauges because 1) they're easier to set up, and 2) the idea of an line full of hot pressurized oil running into the cabin never appealed to me. But I'm willing to be convinced otherwise. Is there are reason I should give up my aversion to mechanical gauges? Doing so would certainly open up some options, as most of the budget-priced gauge sets are mechanical.

I'm in the same boat as you. I need gauges, and don't like the thought of pressurized oil/water coming through the firewall. I would like all VDO electric but they're pricey!

Looking forward to reading some responses here!

Mount mechanicals on the cowl muscle car style? 

I had a mechanical oil pressure gauge in my old Fox body many years ago. I used braided stainless line and never had a problem. The gauge (Autometer) came with a plastic line, but I didn't feel like taking a bath in hot oil it it broke.

In general, I like mechanical gauges because they are more responsive.  But they are definitely more work.

Longacre has an rbc catalog with discontinued and refurbished stuff on their website.  I got a bunch of very good stepper motor electric gauges for cheap-ish.

I've considered buying these many times.  https://www.jegs.com/i/JEGS/555/41290/10002/-1

The giant Jegs logo keeps me from pulling the trigger everytime.

I once had a plastic line feeding my mechanical oil pressure gage. When I started the car up for the first time in a year after an engine rebuild, the plastic line was in contact with the header and my initial joy of the first start was quickly replaced by fear as the engine bay became a bit more flamey than I liked. Turns out 45 psi of oil sprayed onto a header when the ignition timing is way retarded and the header is cherry red is not a good combo. Luckily, I had a extinguisher handy, got the engine off and the fire out and other than the plastic gauge line had no damage at all. Close call.

I still have the same gauge, but with a braided steel supply line routed away from hot things as best as it can be.

Way, way back in the day, when I worked for a VDO W-D, a big advantage of mechanical gauges was the wider sweep: like 270 degrees vs. 90 degrees. 

David S. Wallens said:

Way, way back in the day, when I worked for a VDO W-D, a big advantage of mechanical gauges was the wider sweep: like 270 degrees vs. 90 degrees. 

I think that's the biggest advantage of mechanical, but electric ones will work as well.  It's really a personal preference.  I have mechanical oil pressure and water temp gauges in my 1961 Pontiac and they've been fine, no issues with the connections.  Most oil pressure gauges come with a little nylon tube, if you use it make sure it's routed away from anything that could get it hot or rub on it.

One of my cars has a fuel pressure gauge with a hose running to it. It does make one somewhat uncomfortable thinking that gas leaks will end up on one's lap.

David S. Wallens said:

Way, way back in the day, when I worked for a VDO W-D, a big advantage of mechanical gauges was the wider sweep: like 270 degrees vs. 90 degrees. 

There are plenty of electronic gauges with a 270 degree sweep these days.  IMHO, pressurized oil has no business behind the firewall.

That's doubly (or so more!) true of fuel pressure.  Having a pressurized fuel line in the cabin is an actively safe hazard.

Kreb said:

One of my cars has a fuel pressure gauge with a hose running to it. It does make one somewhat uncomfortable thinking that gas leaks will end up on one's lap.

Fuel pressure isolator! Get one.

I use mechanical gauges in my own cars. Have installed quite a few sets of electric in customer cars (think muscle car era) as accessories or incorporated into a complete rewire. I like the stand alone simplicity of mechanicals personally with their only common bond the wiring for lighting.

Everybody likes pics so here's one of my Firebird with cheap Autogage (by Autometer)  mechanicals because I wanted stock looking gauges to match the stock speedo & tach. Lower Pic is same year Firebird dash I did for a Pro-Touring SEMA car. Custom carbon fiber panel with Autometer electric gauges.

[URL=https://s240.photobucket.com/user/NOTATA/media/Firebird/The14Cardash004.jpg.html][/URL]

[URL=https://s240.photobucket.com/user/NOTATA/media/SEMA%20thrash%20at%20Fletchers/FirebirdTAdashbuild243.jpg.html][/URL]

All I'm saying is that I've got 3 Sunpro electric gauges (temp, oil pressure and voltage) that have done my RX7 well for 11 years. I think I paid $20 for all 3 gauges. Would I trust that the numbers they give me are 100% accurate? No. But I know what the gauges read when the car is running right, and they do *something* when something is wrong.

These aren't the ones I have, but they look pretty cool, retro and cheap:

https://www.ebay.com/itm/SUNPRO-CP8055-MULTICOLOR-BAR-GRAPH-TRIPLE-GAUGE-KIT-2-/253875845276

ETA: I have cheap mechanical gauges in the '66 Plymouth, and they are fine too.

If one is not comfortable with an oil line inside the car then use an electric gauge-it's that simple.  Coolant temperature is different as the coolant cannot enter the cockpit.  I've used mechanical gauges on many race cars and never had an issue. 

Improper installation of any gauge can cause problems.

I went to some lengths to get a braided line made up for mechanical oil pressure in the 2002, only to find that the oil pressure port I was using (distributor housing, IIRC) had pulsed pressure from the cam rotation.

Hydraulic-hammered my nice VDO gauge into Oblivion.

I still like mechanical gauges, but I also think there's a lot to be said for measuring here and displaying there when it's done well. There's been a lot of headway in sending info over wires during the history of the motorcar.

In reply to 02Pilot :

Well for 65 years I’ve had mechanical gauges.  They are vastly more reliable. And I’ve never once had any problem with them. 

No scalding hot oil or water. None of that fear mongering. When they fail it’s normally  at the connection between the motor and the firewall because the motor is vibrating away. And once it enters the drivers compartment nothing is moving.  

So there seems to be at least some degree of agreement here that mechanical gauges are not the oily sword of Damocles I feared. Plastic tubing was never in the cards; several have mentioned braided steel - what about copper? With proper tubing, and a dedicated grommeted hole through the firewall, it sounds like a mechanical set might be in the cards.

Copper tube,long a flexible, over time with vibrations = work hardening, then crack a spill of fluids

At least with oil pressure gauges, the only time you would ever hot oil inside the car is if you had a leak at the gauge. You're really just pushing a column of air inside that little plastic line. Unless you're one of those weirdos who bleeds their line to the gauge.

I have only used mechanical gauges on my race cars. On a street car I might use both. I only use Teflon lined SS hose -3 size for my oil & fuel pressure lines.  

I would use metal line only for very long runs and always SS line at  both ends.  As mentioned copper is a no-no unless it's kept from any movement.

I have used both going back to the 70s and never had a issue. I have had more mechanical gages fail than electric. Particularly oil pressure ones. No leaks or anything they just stop working. Other than that I have no preference. I would assume a quality component of either type should work well for a long time.

The other question we should ask is if the Saab has something pre-existing for the idiot lights that might make this easier for you. People have been able to plug aftermarket electric gauges into stock oil pressure sensors in the past- is there something like that you can use?

Stock oil pressure gague in my '64 corvette was mechanical. Copper tube IIRC. It provided hot, pressurized oil to the interior of the car once. Inconvenient but easily repaired.

So braided steel line over copper. Anybody got a cheap source for such line?

In reply to GIRTHQUAKE :

Having had the cheapo electrical thing already set up, I've been down this road. The oil pressure idiot light switch has been teed with an adapter and a 1/8NPT T-fitting. The water temp wasn't set up yet, but I will have to cut a hose and install a short sleeve with a fitting. The wiring is already done. Thus hooking up a set of electrical gauges would be the easiest route by far, but some of the work I've done should facilitate mechanical gauges to a degree as well.