Positech oil cooler replacement/upgrade needed - solved with viscosity valve

[gyoung]

I've got a Positech P20002C oil cooler on my recently completed RV-6. It's running hot with oil temps ~220F and CHT's above 400F in even a mild climb. I've been holding off drastic action until I got thru the break-in. It now has 11 hrs and temps have not come down much. The engine is an AFP injected parallel 360 with 9.1 compression, piston squirters and one P-mag w/ normal timing/jumper. Cooler is baffle mounted.

I'm in Houston and so far have been flying in mild temps so I know it will just get worse. The Positech was the go-to in 2004 when I bought it (long build) but I sense it's not enough. Is there an upgrade path from there? I tried to search and follow the lineage but the Positech is so old I can't get a clear understanding if what's in use now (like the SW 8406R) is really any better than my Positech. What are my options for a better oil cooler?

 

[gyoung]

Follow-up to close this thread. My troubleshooting took me to the Vernatherm. I found it only expanding about half way meaning the oil was always bypassing the cooler. I replaced the vernatherm with a viscosity valve, aka oil bypass plunger. Flew it today (91 deg on takeoff) and found the oil temp was 15-20 degrees cooler. CHT's also came down almost the same amount. At cruise settings it stabilized about 190 OT and 385 CHT. This was the first flight I've been able to try WOT and the temps stayed below 200 OT and 400 CHT. The oil temp is a bit hotter than I'd like long term but I don't see the need to change the cooler right away.

For any future searches, here are some pics of the vernatherm and bypass valves. The vernatherm guts can be removed by pulling the wire clip and then the empty housing reinstalled to close the hole. For the bypass, you should not need the cap. That's what is closing the hole now. I didn't realize that so spent $30 more than I needed. I bought Superior parts which are WAY cheaper than the Lycoming, e.g. $20 for the spring vs $220. Just use an "SL" prefix for the Lyc part number.

 

[erich weaver]

I might try this. So you are saying don’t order the plug that was included in your parts order? Also, do I understand correctly that the viscosity valve replaces the vernatherm but does not get installed in the same location?
thanks.

 

[Walt]

The potential downside to this is not being able to get the oil warm enough in cooler temperatures.

 

[gyoung]

I might try this. So you are saying don’t order the plug that was included in your parts order? Also, do I understand correctly that the viscosity valve replaces the vernatherm but does not get installed in the same location?
thanks.

Yes. It wasn't clear in my searches that they are 2 different locations. There is a Lyc SL that calls for removing the bypass plunger when a vernatherm is installed so this is a reversal of that. As Walt mentioned, the downside is no thermostat for the oil. Some folks have installed a shutoff ball valve in the oil cooler line to allow manual control. I'm in Houston so not worried about too cold oil and I'm troubleshooting. This buys me some time and is cheaper than a $400 new vernatherm or oil cooler change. <IF> your vernatherm is working properly, the addition of the bypass plunger should make no difference to the max temp. It will block off the bypass the same as the plunger but after ~180 deg. Check your vernatherm for proper operation before making this change.

Here are a couple pics that Dan Horton posted with dimensions.

 

[Walt]

To add just a little more info to this post, the reason I prefer the straight filter adapter is the VT seat is machined perfectly inline with the VT, with the 90 deg and adapter the seat is in the adapter, so it’s not hard for tolerances to stack up causing the VT to not fully contact the seat. Clear as mud right….

 

[Carl Froehlich]

The Van’s Positech cooler was marginal, at best.

My first build use it as that was what Van’s sold. It has since been replaced. It did the job but there are better options.

I suggest you take a look at the 10 row AirFlow Systems 2004X cooler. I use that on my 180HP RV-8 and it is more than enought. I use the 13 row 2006X on the RV-10 IO-540. Both are firewall mounted with a butterfly valve to regulate air to the cooler (needed most of the year to keep oil temps above 180 in cruise).

Carl

 

[gyoung]

The Van’s Positech cooler was marginal, at best.

My first build use it as that was what Van’s sold. It has since been replaced. It did the job but there are better options.

I suggest you take a look at the 10 row AirFlow Systems 2004X cooler. I use that on my 180HP RV-8 and it is more than enought. I use the 13 row 2006X on the RV-10 IO-540. Both are firewall mounted with a butterfly valve to regulate air to the cooler (needed most of the year to keep oil temps above 180 in cruise).

Carl

Thanks. I figured there were better options. I need to replace the Positech but at least now I can do it at a time of my choosing.