Temperature Gauge Faulty?

[skunther]

I got a temperature gauge installed in the pressure relief valve on my 1977 Type 2 bus (2.0 Type 4 engine). The temperature gauge regularly reads ~240 degrees. My mechanic, who did a complete rebuild of the engine, said that at times those gauges are faulty. Well I don't see the point in going through the trouble of installing one if you can't trust it.

Is there any way to verify the accuracy of the gauge? He had suggested buying a laser thermometer gun and using that. I've never used one, but want to be sure I'm not overheating my engine after spending so much on rebuilding it.

Any suggestions?

Much thanks in advance.
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1977 Campervan Pop Top, "Pepe"

[busdaddy]

Spend the $20 on the laser gun, you'll find yourself using it for everything and wonder how you ever lived without one.

A meat or fryer thermometer down the dipstick tube also works if you can find one that's long and skinny enough.
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[furgo]

+1 on laser gun.

If you do find a long enough temperature probe to go into the dipstick tube and compare your readings as busdaddy says, that'd be the easiest thing. I'd be weary about sticking anything that's not designed for it into the sump for fear of it accidentally staying there, though.

Another alternative: if you want to test the oil temp sender and gauge, I'd recommend to do it directly (with the laser gun pointed at the engine block, you're measuring the block temperature, which the sender is NOT measuring).

Back when I did this, I went for a simple "kitchen test". It does reauire removing the sender:

• I connected a 12V power supply to the gauge (you can use a battery instead)
• I connected the temperature sender to the gauge (oil dipstick sender[*] in my case)
• I used the temperature probe on my automotive multimeter (most cheap ones have one nowadays)
• I brought water to boiling point and poured it into a bottle
• I submerged the sender and the multimeter temp probe in the water
• I took readings of the multimeter and the gauge display as temperature decreased

Notes:
• The readings are in Celsius, but you get the gist (100 °C is water boiling point)
• You can heat oil in a pan to further increase the temperature and test the gauge's full range. I skipped that because a) I was simply testing if the gauge and sender combo was working at all b) it was rather messy. The oil temp is also a bit difficult to control under the fire (I did try )
• The compared measurements (multimeter vs. gauge) were reasonably accurate and to my satisfaction (I wasn't expecting high precision from the gauge)
• More pictures on my gallery.

[*] I'm aware there are better options and locations for measuring oil temperature. That's the object of another discussion.
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'79 Westy, P22 interior, FI 2.0 l Federal, GE engine (hydraulic lifters)

Decode your M-Plate

[calo1956]

skunther , I would say go with the Laser gun. You can measure temps of everything with it. I pointed mine directly at the oil plug sender right after shutting the van down, and was satisfied with the result. But besides that, you can go bunkers with it, and measure cylinder head temps, exhaust temps, basically every area of your motor. If nothing else its fun! Also useful for checking brake caliper temps wheel bearing temps etc. Im happy i purchased one. I bought mine on Amazon, but you can get them in any big box home center
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Enjoy the ride....
72 bug
80 westfalia

[RalphWiggam]

Here is my post from when I used a laser thermometer to verify my oil temp sender that is also located in the pressure relief location. I didnt really come to any conclusion other than the gauge and sender were accurate to the senders location. The real question is what is the actual oil temp and why does the relief location read hotter than everywhere else (exhaust right there)?

"
Got some various temperature measurements tonight with a laser thermometer.

Heads (VDO gauge with VDO thermocouple on #3 cylinder):
Gauge - 275
Laser - 294

This is with the laser pointed down the #3 hole in the tin. The 294 is the max it recorded while I was moving it around over the hole.

Oil Temp (pressure relief location mounted sender):
Gauge - 220
Laser
Pass side bottom of sump towards rear - 185
Driver side bottom of sump towards rear - 187
Rear corner of sump - 170
Inspection plate - 190
Pressure relief casting section - 220
Hand on the dipstick test - barely even warm

So I think I can safely assume my CHT readings on the gauge will always be about -25deg from actual. That would explain my low 325 readings on a highway run at 3800rpm. 350 is just about perfect for me.

With the oil temp, I really still don't know what to believe. I know my sender and gauge are reading dead nuts to where it is located but I don't understand why that part of the block is ~30deg hotter than anywhere else. Maybe it's best to take an average of them all? That would be ~ 191deg when gauge reads 220deg.

Thoughts?
"

[Tcash]

To test your hypothesis on the exh creating the higher readings in the relieve area. Construct a rudimentary heat shield and retest, creating the same test parameters as in your initial testing.

Turkey fryer thermometer
https://www.google.com/search?q=turkey+fryer+therm...ent=safari

Digital with remote
http://www.chinatraderonline.com/Food-Prep-Gadgets...075046.htm

Happy Friday
Tcash

[furgo]

[Wildthings]

I believe shooting the bottom of the case seam several inches forward of the rear of the block gives a good reading of the actual oil temps. Run the engine in normal use, say 10+ miles at 60mph and then quickly pull over and shut the engine down. Let the engine sit for a minute or so so the heat from the oil can reach the exterior of the case (yes the cooling fins do work when going down the road cooling the exterior of the case). If you have a carbureted engine you can also shoot the top of the case.

The food thermometer that Furgo shows, attached to the top of the case should give a good results. Covering the probe with some insulating material like RTV silicone might give more accurate results.

[raygreenwood]

When we were discussing this last just a few weeks back.....I found several reputable notations in several places with teating....that this area of the case is in fact commonly a higher temp than almost anyplace else.....and I cant remember the exact reason.....but a large part of it is that its a large mass area....and part of it is that this quadrant of the case has the most hot oil flowing through it.....from the pump, the oul cooler, the filter, the relief valve etc.

Also.....while the laser thermometer definitely has uses....and you should have one anyway because they are too cheap not to......benchmarking oil temps in very close proximity to heat radiating surfaces that are radiating heat in multiple directions.....some across the line of site path of the IR sensor........this is not one of the applications where its useful for more than just a trend. The +/- spread is just all over the place.

I can tell you because my work takes me across a wide range of manufacturing from aerospace, to automotive, to electronics of all type, medical devices, appliance manufacturing etc.......in about 90% of plants and mfg processes....IR laser thermometers are literally written OUT of processes as dangerously inaccurate and only useful as quick checks during R&D.

They are not to be trusted because of how the sensor works and how it gets less accurate over a very short distance and anywhere the line of site air can be contaminated by radiant heat crossing the path.

The best sensor....for cheap money....if you really want to do spot checks on oil and case temps....is having a VOM with a temperature channel and a handful of cheap K-type thermocouples you can put on the ends of rods and sticks to reach where you need to go......very similar to what Furgo just posted. Ray

[skunther]

Thanks everyone - I purchased a laser thermometer from Amazon, awaiting its arrival. I'd do the dipstick method too - Furgo, I'd like to set up a dipstick thermometer similar to what you set up - can you provide more specific info on your setup? I saw you had some sort rubber gasket to seal the sensor at the dipstick opening.[/quote]
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1977 Campervan Pop Top, "Pepe"

[raygreenwood]

[Randy in Maine]

How do you have this thing timed and what weight of oil are you running?

I have found that both of those variables can really impact oil temps.

[furgo]

[raygreenwood]

[Peter - Belgium]

I also use the lasergun to confirm all is good (I get readings around the 85deg when shooting at the case)... specially since my meter goes to full max as soon as I switch on the ignition contact, so disconnected it for now.

Any clues on why the meter would go all the way to the right? faulty sender unit (even though both sender and meter are new and it worked for the first 50km)?
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356 Outlaw built: https://www.thesamba.com/vw/forum/viewtopic.php?t=430774&highlight=

[furgo]

[Peter - Belgium]

[blues90]

The sump plate VDO sender is variable. @ room temp say 75 degrees it should read 1K ohm. As the temps rise the resistance goes up. I assume you have the 300 degree F gauge and the proper sender. Just to rule things out check the ground from the sender body to the sump plate or the case , should have no resistance . If that's fine then check the connection on the sensor.