Sticky vernatherm?

[agent4573]

Do vernatherms ever stick? My oil temperature on climbout will increase until about 220, then almost immediately drop back down to around 190. In steady cruise the temp will be around 185-190, then, for what appears to be no reason, the temp will climb to 220 over the course of a minute or two. It'll stay there for 30-60 minutes and then randomly drop back down to 185 over the course of a minute or so. Currently running 55-60psi in cruise. Was thinking about increasing that a bit to see if the extra pressure would help open the oil cooler circuit as the temps come up, but besides that I think I have to tear off the accessory case and do some inspections of the vernatherm. Anyone have any experience like this?

 

[Webb]

Check both ends of the engine ground strap first. Dirty or loose connection plays havoc with oil temp readings.

 

[agent4573]

Check both ends of the engine ground strap first. Dirty or loose connection plays havoc with oil temp readings.

I'll double check it, but I have an extremely electrically dependant engine. If the ground strap was loose, it would likely manifest in way more serious issues.

 

[bjdecker]

Sanity checks

Yes, Vernatherms can fail - usually retracted (cold position) or the nose cone isn't seating so oil isn't making it to/thru the cooler. But, would need a couple of additional data points in order to help resolve this issue --

1. Engine Type (IO-xxx-xxx)
2. Oil Cooler size/make/model
3. Oil Temperature Probe type (1 wire, 2 wire, 3 wire?)
4. EIS/EFIS instrumentation kit -- what's the data look like?

Generally speaking, oil pressure will track inverse of oil temperature. Dramatic changes in oil temperature without a corresponding rise or drop in oil pressure points to an instrumentation (oil temp sensor/sender) issue.

Oil is a fluid, and has mass, so be suspicious of temperature changes that appear to be step-function changes, e.g. 185°F then 220°F in under 5 seconds. Laws of Physics still apply ... even in Australia

And, while having good grounding of the engine is critical/essential, in the case of a 2 wire probe, it won't be bothered by the absence of an engine ground.

 

[agent4573]

Yes, Vernatherms can fail - usually retracted (cold position) or the nose cone isn't seating so oil isn't making it to/thru the cooler. But, would need a couple of additional data points in order to help resolve this issue --

1. Engine Type (IO-xxx-xxx)
2. Oil Cooler size/make/model
3. Oil Temperature Probe type (1 wire, 2 wire, 3 wire?)
4. EIS/EFIS instrumentation kit -- what's the data look like?

Generally speaking, oil pressure will track inverse of oil temperature. Dramatic changes in oil temperature without a corresponding rise or drop in oil pressure points to an instrumentation (oil temp sensor/sender) issue.

Oil is a fluid, and has mass, so be suspicious of temperature changes that appear to be step-function changes, e.g. 185°F then 220°F in under 5 seconds. Laws of Physics still apply ... even in Australia

And, while having good grounding of the engine is critical/essential, in the case of a 2 wire probe, it won't be bothered by the absence of an engine ground.

IO-375 from aerosport.
13 row cooler 2006X Airflow systems.
Temp probe is a 2 wire 494-70004-00 Oil Temperature, RTD, 5/8-18 UNG-3A that comes with the Garmin g3x engine sensor kit.
Engine monitor is the Gea24 paired with the g3x.

I'll pull a log next time I go to the airport. It's not a step change in temp, but a fairly rapid rise/fall over 30-60 seconds. Oil pressure is constant through the swings.

 

[lr172]

Yes they can sick and sometimes they will eventually move again. the clearances on the moving piston are pretty small. I had one that wouldn't move. I took it apart and cleaned out all of the sludge and carbon build up and is still working 1100 hours later. There is a large C clip that must be removed to get it apart and need to be cautious, but sticking VT's can typically be restored. THe wax plug is supposed to be there so don't disturb it; Just cleaning out the sludge and carbon.

Larry