Transmission thermostat

For the last couple months (the truck hasn't been used and it's been too cold to work on it) I've had an issue with loosing radiator fluid. Engine runs just fine and no leaks other than around the water pump. Yesterday I replaced the water pump and thermostat. While doing so the radiator fluid looked like someone had put radiator stop leak in it (or so I thought). Engine oil level looked good and the right color so I hoped the problem was the water pump. After replacing it I noticed the trans temp gauge reading unusually hot (not in the danger zone but much hotter than normal) after a few minutes of light use.

The radiator fluid leak appears to be where the radiator fluid and transmission oil come into contact with each other. My truck has the 5.7 with the tow package and the external cooler in front of the radiator so the only place the problem can be is where the transmission thermostat is. Without a trans dip stick I can't check the level without putting it up on my lift. After searching I haven't found much information or pictures.

I was hoping someone had a picture or some information. Also I'm going to need lots of trans fluid as I'm guessing it's got a mixture in it just like the radiator. Does anyone know how much the system holds? I suspect that I'll be doing more than one change before having it flushed.

 

I’ve never heard of a transmission thermostat ????

 

I removed it. Surprisingly it's easy to get to. It's mounted on the side of the passenger's side of the transmission. There's two parts to it. A trans cooler that has two coolant lines going to it and two holes for trans fluid. those two holes have o-rings around them and mount to the thermostat. The thermostat is just a flat plate about 1/2" thick with an adjuster on the top. Since the radiator fluid only goes to the cooler I'm guessing that's what's bad. I tried testing it by putting air to one of the trans fluid holes and plugging the other one to see if air leaked out the coolant lines but it seamed tight. However it's cold.

 

Yep, sounds like your transmission and engine cooling system are "exchanging fluids".

The AB60 transmission has a warmer/cooler on the side of it that takes engine coolant off at the heater supply hose near the firewall and returns the coolant to the heater return hose. When the engine is first started, and before pressure builds in the cooling system, the transmission fluid pressure must be high enough to force fluid into the engine cooling system. Once the engine cooling system gets to temperature and pressure, coolant may go the other way.

First, I believe I would replace the warmer/cooler, or at least remove and inspect it. I doubt that it has any replaceable parts, but it would be worth checking out. It has some radiator tubes inside that warms the transmission fluid until the thermostat opens, and then the warmed fluid is sent to air/fluid cooler up front. There have been other posts here about the warmer/cooler leaking.

System fluid quantity is approximately 13.0 quarts for the AB60; for component replacement, drain pan (2.2 qts), valve body (5.0 qts), and torque converter (5.7 qts). Once you've fixed the leak, you should probably flush and fill the engine cooling system, and then flush and fill the transmission. If you want the best for your truck, DIY:

https://www.youtube.com/watch?v=fLVZSoKbyZ0

 

The transmission cooler isn't cheap, $300, but it's the only part that seams to have both coolant and trans fluid so I ordered it. Is there an alternative to Toyota's tans fluid? I would like to use something cheap to flush the system out. Since it's going to be in the transmission for such a short time and I'll be using plenty of it the cheaper the better. Once it looks like there's little coolant left in the system I'll have it flushed with Toyota fluid. I also have a filter and pan gasket coming for the trans. The good news is that I can flush out the tans cooler pretty easily right now as the thermostat block is removed. Getting it all out of the torque converter is what will take time. I'm wondering if I can just remove the pan and filter and put a hose into a container full of fluid and turn the engine over to suck good stuff in while the bad will just flow into a plastic tray under the tranny.

 

For what it's worth: https://www.tacomaworld.com/threads...a-ws-atf-automaitc-transmission-fluid.373083/

Pick the cheapest one that works for you in the flushing phase. For the final fill, I would go with the real deal, Toyota WS.

The only clue to your location is your Tundra in a field of snow.

If you live in the rust belt, removing the pan may be a decision you regret...corroded pan bolts can easily snap off, leaving you with a bigger problem. Not saying not to do it, but just be advised...maybe you can get a clue on the first bolt. It would be nice to remove the pan, change the strainer, and wipe everything clean that you can.

One full flush will probably get it 95% clean. I would not try to do this with the transmission partially disassembled. I would install the new warmer/cooler, reattach all the plumbing, and follow the video for the flushing. It'll be hard enough without any added complications.

See above. I would not try to get innovative on this...just follow the video.

At least on the engine coolant side, there are cleaners for aluminum systems that will aid in cleaning the cooling system up faster.

 

The truck is from South Carolina so no problem with removing bolts. With the pan off I was able to remove about 2 quarts more of the bad fluid and with it up on the lift with the pan off anything that would of drained into the pan is also removed. The trans filter seams like it has a check valve built into it as when I removed it a lot of fluid came out. I blew air through the lines to the trans cooler in front of the radiator and got plenty more out. It'll be a few days before the part arrives so the more that drips out the better.

I'm not worried about the cooling system. Once it's warm out I can flush that with ease with water. The pink slim is really slippery and doesn't seam to mix well with the coolant. It seams to like to end up in the expansion tank.

 

Does anyone have the torque specs for the thermostat bolts?

 

@Dr_Al Did you get have update to your issue? would be good to get a resolutions good or bad on what seem to fix the problem you had. Thanks.

 

Not to hijack your thread ....... I have the thermostat on my Tundra "pinned" open. Since I only use mine for towing (RV and horses), pinning it open has helped to control (lower) trans temps, as measured at the torque convertor and with an ultra gauge.

 

Replacing the the "tuna fish can" heat exchanger on the side of the transmission fixed the problem. It took plenty of flushes to get the color of the fluid (bought the Valvoline AFT in cases). It could use another flush but I've been lazy. The only issue is the torque converter clutch sometimes pulses when it's locking or unlocking. But the '07 and '08 Tundras have an issue with this. I didn't do anything more than just remove the oil pan from the bottom of the transmission and spray 100% IPA into it to clean off as much of the bad oil as possible to speed up the flushing process and change the trans filter. I have towed 8000 lbs with it without issue so I haven't worried about swapping out the TC.