Transmission Thermostatic Bypass?

[peteco]

Any recommendations on a transmission thermostatic bypass for a 2006 Roadtrek 210 Chevy 6-liter with 4-speed transmission?

Here are a couple on Amazon. The first one (blue) looks like it is one piece which may be less susceptible to leaks.

https://www.amazon.com/dp/B008BTJFJ4...60916&sr=3#Ask

https://www.amazon.com/dp/B004XUDPAK...=2UMOED3LD6D36

[booster]

No experience with the first one, or the style of it. It wouldn't work for me anyway as I don't like hose clamp connections on cooler lines. Others have no issues and do use them, so personal choice.

On the second one, no experience with the Derale brand of that style, but did use Setrab of essentially the same style on the van for a while. The trans got hotter than I liked with it on, but can't specifically blame the the thermostat because, as most know, cooling is still iffy. I did test it on the bench in a pan of hot oil, and found the internal bypass valve did not seat fully until nearly 220* on a 180 degree thermostat. The sealing surface was just a stamped sheet metal piece the spring pull down over the bypass opening, so not a stellar seal, it appears.

I am currently running one of these in 185* setting:

High-Flow Engine Oil Cooler Thermostat, 185F FSM-185

They claim less than 1% leakage at under 5* above setpoint and use a sliding sleeve for the valve. It passed the bench test easily with no measureable leakage that I could see. They certainly aren't inexpensive, especially when you get them with the AN style fittings, but I was impressed with the quality.

If you do put on a thermostat, by ready to see some fairly wide temp swings, as the thermostat is measuring a different temp than the Scangauge or a pan temp gauge does. It will look pretty good in hot weather and constant use patterns, although the temp will likely read higher on the Scangauge and lower on a pan sensor than the setting temp. Hit a big hill early in a drive before all the oil gets hot in the pan, and the Scangauge will shoot way up quickly beyond the thermostat setting and the pan will still be much cooler.

The Improved Racing one we have now is rebuildable, so I bought all 3 temp ranges, 145/165/185* of thermal actuators, as they are easy to change. Currently running the 185*, but may move back to the 165*. I am going to wait until I know for sure what the torque converter lockup changes do for us. At 185* you don't get the benefit of a cooler pan fluid temp, which buys you a bit of extra time before you get too hot (it won't change how hot you get, just how fast it happens)

I have two of the Setrab thermostats if you want one, but you would have to buy the Setrab connectors in whatever style you would want to use, as I used AN fittings that I am going to save as spares for the Setrab cooler connections.

[Hondo]

I used the Derale on 2 different RVs without any issues, works excellent.

Jamboree-



Roadtrek 210-

[peteco]

Booster,
I have a Hayden cooler with fan that has hose barb style connectors on it. So unless I get special hoses made up I may need to stay with hose barb connections. I have started using PEX type cinch clamps which are more uniform clamping than a hose clamp. The Setrab looks the same as the Derale; do you know the difference?

[booster]

Originally Posted by peteco

Booster,
I have a Hayden cooler with fan that has hose barb style connectors on it. So unless I get special hoses made up I may need to stay with hose barb connections. I have started using PEX type cinch clamps which are more uniform clamping than a hose clamp. The Setrab looks the same as the Derale; do you know the difference?

I don't know the internal parts appearance, but from the casting it appears the actuator sits in the same way, so likely similar.

The crimped band clamps are a good idea for sure. One thing that has seemed to become common on barb fittings is to double up on the clamps, either with regular hose clamps or crimp types. I have heard of lots of folks that had leaks or even blown off hoses curing the problems by double clamping. That is what I did on the my old Roadmaster when the OEM cooler line started leaking at the factory crimp. Cut off spliced in a section of rubber hose between the tube ends with double constant pressure clamps.

I will point out that unless you are right on the edge of not having enough cooling, like the Chevies tend to be when climbing big hills, you won't have an indication of if the thermostat is leaking or not. The only way is on a flow bench, or checking it static by heating it in a pan of oil and checking for oil coming through the bypass as you pour it through one side.

It would be interesting to see what the construction is on the first one you list, as it looks like it is not like the Setrab or Derale, which are the typical style we have seen for decades.

[Hondo]

On the Jamboree I used fuel injector hose clamps, on the Roadtrek standard ones... no leaks so far with either setup though I will probably double up on the RT just to play it safe.

[peteco]

Originally Posted by Hondo

On the Jamboree I used fuel injector hose clamps, on the Roadtrek standard ones... no leaks so far with either setup though I will probably double up on the RT just to play it safe.

I have used fuel injector clamps also. They are a lot better than hose clamps. It is getting harder to find quality hose clamps that don't bind or strip out.

[booster]

McMaster-Carr stil carries a good assortment of ear crimp clamps, and are very easy to deal with. They even have the no gap ones.

https://www.mcmaster.com/#ear-hose-clamps/=1aeqd6g

[peteco]

Home depot has a few sizes for PEX tubing.

https://www.homedepot.com/p/Apollo-1...FRJ6YgodAkkFNA

[booster]

We just got back from a 440 mile, on day, trip to get the van rustproofed with Corrosion Free, now that they have one somewhat nearby.

Current setup is:

No transmission fluid to radiator

Both Setrab coolers used for trans cooling. Rated at about 60K btu IIRC

Dual Spal fans in front of radiator also pull through Setrabs

Improved Performance 185* thermostat bypasses both coolers

Scangauge and pan temperature readings for trans

Conditions were 40-50*F on two lane, somewhat rolling hills, highway with a bunch of small towns. Speed at 59mph for the most part, except for towns.

Once everything settled in to steady state, which took about 30 minutes, the temp readings were surprisingly steady at 194* at the Scangauge and 180* at the pan, although the pan temp dropped about 5* when we went into a huge headwind, likely because the coolers were getting much more air.

It is kind of interesting to try to figure out what is going on. The 194* out of the trans makes sense, as the thermostat should be holding the the temp that it sees in the cooler line out of the trans at 180*. The cooler line usually comes out of one of the hottest spots in the trans, but it appears that the Scangauge temp sensor is in a warmer place. Some of the cooler return goes through the valve body and some goes to the pan, I think, plus some of the trans flow comes out of the valve body to the pan without going to the cooler, so near impossible to know exactly what is going on.

How it reacted to increased load and heat was also a bit unexpected. If you hit a long hill, or got into a town stop and go situation, the Scangauge and pan temps would drop pretty quickly, in a matter of minutes. I have to assume that the thermostat is reacting quickly to the increased trans outlet temp and sending lots of cooled oil back to the pan and valve body areas. In the coolish weather we were in, the coolers would have been pretty cold going down the highway, I think.

All of this won't be directly applicable to those that have the trans fluid through the radiator and then the smaller than we have external trans cooler, as, based on what we saw when we had that setup, the radiator does a major part of the cooling and also the setting of the actual trans temp. In 40* weather with that setup, we would see quite cold trans temps, often in the 125*-135* range, presumably because the exit end of the radiator, where the trans cooler is, was running very cool in the low temps. For this reason, I think if you are going to be in coolish weather much, putting the thermostat before the radiator, so it bypasses both coolers, would be a good idea instead of just bypassing the secondary cooler.

All the thermostats I have seen allow some flow to the coolers even when in their full bypass position. When you look through them, they are wide open in the bypass and to the cooler, so how much goes to the cooler will be determined by the flow resistance of the bypass passage vs the hoses and cooler. They often peg it at 10% to the cooler while in full bypass, but in reality I don't think they don't have any idea how much it really will be as it will change with the cooler flow resistance and oil viscosity. For this reason, even with the thermostat, you may run cooler than setpoint in the coldest weather.

For reference on our Chevy:

Owners manual says to check trans fluid at "normal operating temperature of 180-200*F". This would have to be the Scangauge read internal sensor, I think, so they like them pretty hot in normal use..

The internal temp sensor appears to by on the bottom of the valve body, so probably right above the actual pan fluid level. It would see the heat transferred through the metal parts, I think, and may be in fluid return flow from some of the areas of the trans.

[Hondo]

Interesting results.

My Rt seems to run at 175-185 most of the time and it will increase to 205 on a long tug through the mountains west of Denver. Where I really appreciated the Derale thermostat most was when I was testing in winter temps and came down I-70 into Sliver Plume, a long idle descent in 30F temps- the trans temps remained in the 180F area as it regulated flow to the cooler.

Without the thermostat I saw a downhill temp of 135F or so, wild swings readily apparent.