TheNortherner
Active member
8GCBC Scout, O-360-C2A with oil screen that had a 2018 IRAN and what was called a crankcase overhaul but otherwise original engine.
The problem:
From the oil level thread and a discussion with my mechanic my oil is running too cold. 140F basically always, down to 120F when it's -20C. We have tested my gauge and it reads 3-4 low in the whole range up to 200. During the spin on adapter we investigated the length of the vernatherm and it is in the open position (retracted when cold). There is witness marks on the sealing surface. We wondered if the new sealing surface on the .75" spacer with the spin on adapter would change the temperatures or provide a different length. It did not, post oil adapter my temperatures are the exact same. It seems too much oil is going through the cooler and not enough through the bypass. I take off 80% of my cooler and my temps rose to 160F. I fully taped the cooler off and they run at 180 now in cruise and if I'm rude to it I can hit 190 but they come back down to 180 when I level out and pull power. My CHT is on cylinder 3 and runs about 300-310F in cruise and 330F Climb. max angle climb extended I can get to 350. Engine runs cold
Research:
-The oil when cold can travel directly from the pump into the filter supply, there was an oil plunger on some engines in the bypass route before the cooler. The plunger used pressure from cold oil resistance in the cooler to push it up and bypass the cooler
-The vernatherm when hot extends and closes this bypass, when it cools it opens and allows more oil to bypass the cooler.
-The oil can come out of the pump and flow through the cooler at all times, it's just a more restrictive route.
-Some oil is always circulated through the cooler to prevent it from thickening too much during cold operation which supplies the accessory case.
-No reports of a vernatherm failing in a way in which it opens too early and engines run cool.
-Other Scouts in the area have oil temps in the 170-190 ranges, open oil coolers.
For Opinion:
-My 74 spent its whole life on floats(except 1975), the exit on the cowl only has a small 2" wide aluminum lip and no cowl flap as mentioned in the manual. Did the early aircraft come without ground adjustable cowl flaps? Was it removed to make a bigger hole for more cooling as a float plane? Could this extra airflow be significantly contributing to my cold running engine?
- Could my aircraft have both a plunger and vernatherm installed?
-Likelihood of just a vernatherm which is opening too early?
-Any other thoughts on why my engine might run cold?
Thanks!
The problem:
From the oil level thread and a discussion with my mechanic my oil is running too cold. 140F basically always, down to 120F when it's -20C. We have tested my gauge and it reads 3-4 low in the whole range up to 200. During the spin on adapter we investigated the length of the vernatherm and it is in the open position (retracted when cold). There is witness marks on the sealing surface. We wondered if the new sealing surface on the .75" spacer with the spin on adapter would change the temperatures or provide a different length. It did not, post oil adapter my temperatures are the exact same. It seems too much oil is going through the cooler and not enough through the bypass. I take off 80% of my cooler and my temps rose to 160F. I fully taped the cooler off and they run at 180 now in cruise and if I'm rude to it I can hit 190 but they come back down to 180 when I level out and pull power. My CHT is on cylinder 3 and runs about 300-310F in cruise and 330F Climb. max angle climb extended I can get to 350. Engine runs cold
Research:
-The oil when cold can travel directly from the pump into the filter supply, there was an oil plunger on some engines in the bypass route before the cooler. The plunger used pressure from cold oil resistance in the cooler to push it up and bypass the cooler
-The vernatherm when hot extends and closes this bypass, when it cools it opens and allows more oil to bypass the cooler.
-The oil can come out of the pump and flow through the cooler at all times, it's just a more restrictive route.
-Some oil is always circulated through the cooler to prevent it from thickening too much during cold operation which supplies the accessory case.
-No reports of a vernatherm failing in a way in which it opens too early and engines run cool.
-Other Scouts in the area have oil temps in the 170-190 ranges, open oil coolers.
For Opinion:
-My 74 spent its whole life on floats(except 1975), the exit on the cowl only has a small 2" wide aluminum lip and no cowl flap as mentioned in the manual. Did the early aircraft come without ground adjustable cowl flaps? Was it removed to make a bigger hole for more cooling as a float plane? Could this extra airflow be significantly contributing to my cold running engine?
- Could my aircraft have both a plunger and vernatherm installed?
-Likelihood of just a vernatherm which is opening too early?
-Any other thoughts on why my engine might run cold?
Thanks!