Thermal bypass for trans.
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Senior User
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From: Pleasant Lake, IN
Thermal bypass for trans.
O.K. help me get my brain around this...I'm looking at a thermal bypass to use along with a tru-cool trans cooler. The thermal bypass says that it opens fully at approx. 180*. That seems a little high to me. I would think that it should be fully open and letting all fluid run through the coolers by about 150* so it has a chance of staying at say 150-175*. Am I thinking wrong, does the 180* mark sound right? Isn't it basically acting like a thermostat for the trans. I'd think that if it's not fully open 'til 180* there's no way that the trans temp can ever be below 180* except when it's first warming up, of course.
Lead Driver
Joined: Jun 2003
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From: Damon (South East Texas)
Your thinking sounds correct. The thermal bypass would restrict flow until the setting for which it was designed. 180* would seem to be too high. I don't know too much about the temp ranges available because I live in a warmer climate and have only the factory pressure bypass valve. From what Mark said it would bypass fluid if it were cold and thick enough.
Frmr Ford Trans Engr
Joined: Aug 1999
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From: SE Florida
Your thinking doesn't sound right to me.
The fluid going to the cooler is right from the torque converter. This is the hottest fluid in the trans, and can be A LOT hotter than the average trans temp. The trans temp will stay about 20-50F below the thermoset setting in the cooler line. The cooler COOLS the fluid going through it, so the fluid going back to the pan is going to be A LOT cooler than the thermoset setting.
There's a reason you won't find a thermostat below 180F. Those that make thermostats understand how they work.
The fluid going to the cooler is right from the torque converter. This is the hottest fluid in the trans, and can be A LOT hotter than the average trans temp. The trans temp will stay about 20-50F below the thermoset setting in the cooler line. The cooler COOLS the fluid going through it, so the fluid going back to the pan is going to be A LOT cooler than the thermoset setting.
There's a reason you won't find a thermostat below 180F. Those that make thermostats understand how they work.
Lead Driver
Joined: Jan 2006
Posts: 7,308
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From: Hartford, WI
Your thinking doesn't sound right to me.
The fluid going to the cooler is right from the torque converter. This is the hottest fluid in the trans, and can be A LOT hotter than the average trans temp. The trans temp will stay about 20-50F below the thermoset setting in the cooler line. The cooler COOLS the fluid going through it, so the fluid going back to the pan is going to be A LOT cooler than the thermoset setting.
There's a reason you won't find a thermostat below 180F. Those that make thermostats understand how they work.
The fluid going to the cooler is right from the torque converter. This is the hottest fluid in the trans, and can be A LOT hotter than the average trans temp. The trans temp will stay about 20-50F below the thermoset setting in the cooler line. The cooler COOLS the fluid going through it, so the fluid going back to the pan is going to be A LOT cooler than the thermoset setting.
There's a reason you won't find a thermostat below 180F. Those that make thermostats understand how they work.
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Senior User
Joined: May 2008
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From: Pleasant Lake, IN
Alright, that's good to know cause they don't have any other options as far as temp. settings. I was thinking that this thing was going to redirect the fluid right back into the inlet line untill the fluid is up to 180*. Is this the same style that you're used to working with Mark? Remote external thermal bypass: Bulkpart transmission parts I must be a little more with it today, It's making sense in my head now. Talk to y'all later...
Post Fiend
Joined: Jun 2006
Posts: 9,714
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From: White Mnt's,New Hampshire
The Ford R4100 automatic transmission has this device installed on the passenger side between the two cooler lines. It's designed to bypass the cooler when fluid temps are cold to aid in quicker warming to operating temps. It will also bypass fluid if the coolers are blocking flow for any reason. This device can fail at some time. If you find yourself having higher than normal operating temps or temps climbing out of control while your towing, chances are this little device is your problem. It's an easy install. It takes about 20 minutes and you lose very little transmission fluid. See below how to tell if this is your problem.
1999-2003 Ford 4R100 Transmission Cooler Bypass Valve
1999-2003 Ford 4R100 Transmission Cooler Bypass Valve
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Senior User
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From: Pleasant Lake, IN
right, I've read that, but a while ago Mark and I were talking about trans. and he said that that thing is a pressure bypass deal and not really a thermal bypass valve and he recommended using one of the thermal bypass valves, I think like the one that I linked to.
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Post Fiend
Joined: Jun 2006
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From: White Mnt's,New Hampshire
guess i dont understand what your trying to do..i have a stock bypass with a true cool..my gauge has never been over 160 but once..that was towing a 32 ft 5th wheel..the trans hit 180 then.....the winters up here are 7 months long and below 0 quite often and have yet had trans problem do to cold weather..the trans was rebuilt a year ago..but having 160k miles on the weak early 99 TC did that one in....im sure Mark will set you strait....good luck
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From: Pleasant Lake, IN
Well, what happened was I had asked about a tru-cool trans. cooler. One of the models they had came with NO thermal bypass, another model they carry comes with an external, remote thermal bypass. When I asked which of the two I would need, Mark said that he highly recommended getting the one WITH a remote thermal bypass. He explained that the thing on a factory trans. is NOT a thermal bypass, but rather a pressure bypass. mostly there in case of a cooler blockage the entire trans. would not be ruined. I'm not sure how to link to a previous thread, so you can read the original question and answer. But none-the-less, Mark has suggested using one so that's why I am looking at them. I don't know too much about auto trannys, that is one thing that I've never gotten into much, but always wanted to. I'd love to know all the ins and outs and hows and whys about them, but have never been into one any deeper than changing fluid and filter.
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From: Pleasant Lake, IN
O.K. got it, it was discussed in a thread titled "Trans cooler fan" started by John M T on 6-5-08. There you can read what Mark said about the two bypasses. It appears that I did not post in that thread, I read it then PMed Mark with some other questions. Yeah, that's how it was, I'd forgotten that it was in that thread about cooler fans.
Post Fiend
Joined: Mar 2007
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From: Texas
From what I read, you understood him correctly. Here's the link you were looking for.
https://www.ford-trucks.com/forums/7...-on-trans.html
https://www.ford-trucks.com/forums/7...-on-trans.html
Lead Driver
Joined: Jun 2003
Posts: 8,298
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From: Damon (South East Texas)
Your thinking doesn't sound right to me.
The fluid going to the cooler is right from the torque converter. This is the hottest fluid in the trans, and can be A LOT hotter than the average trans temp. The trans temp will stay about 20-50F below the thermoset setting in the cooler line. The cooler COOLS the fluid going through it, so the fluid going back to the pan is going to be A LOT cooler than the thermoset setting.
There's a reason you won't find a thermostat below 180F. Those that make thermostats understand how they work.
The fluid going to the cooler is right from the torque converter. This is the hottest fluid in the trans, and can be A LOT hotter than the average trans temp. The trans temp will stay about 20-50F below the thermoset setting in the cooler line. The cooler COOLS the fluid going through it, so the fluid going back to the pan is going to be A LOT cooler than the thermoset setting.
There's a reason you won't find a thermostat below 180F. Those that make thermostats understand how they work.
Thanks once again for your transmission answers. I am learning more and more about their operation. Your explanaion makes a lot of sense to me now.
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