How stable is your oil temp gauge ?

I have the built in VDO as well as a stand alone VDO. The built in never moves more than 1/4". The stand alone works well for about an hour or so. I've checked the temp readings with a dipstick gauge and it's pretty close. But after an hour or so of driving, the gauge starts acting like a tachometer and rises/lowers with the rpms. This usually happens after a couple years on the sending unit. I'm on my third sending unit now.

Best to calibrate your temps with a dipstick unit and your built in. Mark your built in with a sharpie and periodically check it.

I'm planning on getting a new stand alone through Aircraft Spruce. Obviously not another VDO. 

Once you get familiar with your engine you really don't need the gauge. You can  usually tell if your car's running hot by the way it's performing...and smelling.

 

My good friend, Joel Schlotz, always tells me, "Don't worry about it, just drive it!"

No you can't have the sender hooked up backwards, the switch side is either on or off, you wouldn't have normal gauge movement if it was connected.

Why do you have the pressure warning light connected as a temperature warning instead? Do you have some other oil pressure gauge or warning light in use? Oil pressure is a lot more critical to know than temp.

Justin,
Sorry for the confusion... I have on side of the vdo sending unit set up to the standard VW 'idiot light' on the Speedo. I assumed that was always oil pressure. The other side is to the oil temp gauge.

Ted

My oil temp needle has never made it past the middle. It takes time to get there and then sits in the middle. I don't do much stop and traffic though. Usually hit the highway or a mountain road and I don't stop much.

Ted, my combi gauge starts out almost the same, except I'm on the left side of the green at the lower temp region. Mine gets warm slowly, usually residing about 1/3 up the scale, and staying there. My external(no internal) cooler and thermostat take care of the temp and it never gets above 5/8 on the gauge. The oil thermostat and fan thermostat are both set for 180, so I'm pretty sure that 1/3 to 1/2 of the gauge is 180.

 

Oil pressure and cylinder head temp are more important than oil temp IMHO, but oil temp would definitely be third for me.

The dual sender is oil pressure only, one post for a gauge and one for a pressure light.

 

You should have a different sender for temperature. 

Right, VDO makes temp sensors with temp warning switches and they make pressure sensors with pressure warning switches but they don't make temp sensors with pressure warning switches.

 

Ted, owing to Chinese quality control, everyone's gauge is different, but here's a summary of how mine behaves and how I 'fly' it. I think the dipstick oil temp is about 190 degrees when the needle is at mid-gauge.

 

 

 

 

I have a 2028 cc stroker (90.5 x 78.8), and live in the central valley, with 95-degree (or more) days every day from May to October. I recently upgraded to the Setrab cooler that's a step larger than yours and had it moved to the wheel well. I control its fan manually.

 

I haven't run the new cooler in anything above 80 degrees yet, but it definitely cools better than the stock VS mesa cooler mounted in the compartment ahead of the engine bay. Even with the mesa cooler, I've seen the gauge up to the 'shut down' point only once - on a 95-degree day, climbing steep freeway hills at 75 mph, with an additional bulkhead fan running that drew air from the hot cooler compartment into the engine bay. I never again turned that extra fan on and never again saw oil temps that hot. With the Setrab, I haven't yet seen the gauge above the midpoint.

 

I think the engine builder installed a VDO sender, but the gauge seems to behave the same as it did with whatever VS installed in their 'stock' 1915.

 

 

Hmmm...  In almost nine years of driving in sultry Charleston I've never seen mine above "Starting to get stressed."  Kudos to the Setrab.

Ted, do you have this?

Or this?

The first option gets two separate senders, the small threaded opening for oil pressure idiot light sender, and the second for oil temperature, bigger diameter sender. One wire each.

 

The second photo is a dual oil pressure sender, one wire for idiot light and one for a pressure gauge.

Both...

On my 1600 I have the top one. (Which explains why the temps were appearedly so stable).  On my 1915, I have the latter. (Which explains why the 'temps' appear so unstable on the 1915)

Thanks for the info!

Ted

Nice thread folks. Another educational tool!

Thanks to all, Art.

Agreed. Very informative!

Thank you all,
Ted

My temp gauge always used to read in the bottom 1/3'rd of the line and I didn't like that, especially when Chris borrowed the car for a weekend or something, so I added a resistor, the value of which was found by trial and error, such that when it's sitting at 200°F it's just about mid-scale and when it's at 220ºF and I'm starting to get worried it just starting to get close to the right hand block.  I found with a cup of hot olive oil from the microwave that 230ºF is inside of that right block, so I just tell Chris "Keep it left of the right block" and we're all fine.

 

As far as I now, it never goes above 3/4 scale.

 

That said, ALL senders are different and will typically give different readings.

Your gauge behavior makes sense if you have a temp gauge hooked to a pressure sensor. First, the fact that it fluctuates noticeably with RPM. Second, a temp sender will typically decrease in resistance as temperature increases, a pressure sender will typically increase in resistance as pressure increases. Essentially the right side of your temp gauge represents low oil pressure, the left side represents high pressure. Hence why it starts out on the left and moves to the right as the engine warms up, sits on the right at idle and moves left as you rev the engine.