Operating Temp-- Transmission & Engine

[TRDFerguson]

I'm driving my 1998 from Northern California to Michigan for a new career.
Nevada

Nebraska

(I put the running boards back on to avoid having to move them)

I'm worried about my operating temps. I have a ScanGaugeII, but my '98 has no transmission temp sensor so I'm a little in the dark there.
According to my scanguage, my coolant temp is never under 210F and is usually around 215F. By my reasoning, my transmission fluid temp can't be less than that because it is using the coolant as a heat transfer medium.

I've found that the normal operating temp for the 5vz-fe is 176F-203F. Im never in that range. I wouldn't think that the engine would care about being a little higher than that, my concern is the transmission fluid.



I replaced the transmission (myself) last month. I replaced my radiator last year (a Denso unit) and use red Zerex HOAT coolant. The thermostat and water pump are OEM and ~ 40k miles old. I've never seen the temp gauge any higher than how it looks in the picture.

I worry about keeping the transmission fluid at ~215F for around 11 hours per day like I've been doing.

Questions:
Why is my coolant temp so high? Is my confusion that the scanguage is telling me the temp before it is cooled?
Am I playing with fire by driving so far with trans fluid temps that high?

For what its worth, I averaged 21.5MPG having cruised at 80 MPH for most of the 800 miles. So shes running well overall.


Thanks--- I have a lot of time on my hands to obsess over things like this (driving alone)

 

[mtbtim]

It sounds like your thermostat might have been installed incorrectly. There's a jiggle valve on the thermostat and it's suppose to be in the 6 O'clock position (pointing towards the ground). There's people on this forum who have reported their coolant temps were higher because of it. I've been using a OBD II bluetooth sensor with the Torque Pro app on my Android phone and I usually see no higher than 195 degrees.

Your engine coolant temp is not an indicator of the temperature of your trans fluid. Before I installed a B&M 70264 cooler in-series with the stock cooler in the radiator, my engine coolant would stay around 190 while my trans temp would be around 150-160 driving down the highway. If you drive over a mountain pass, the trans temps will start to climb quickly. Also, the ambient temperature does affect the trans temp. I'm learning that right now since it hit 100 degrees in San Jose, CA today.

A trick I learned on this forum is to turn off your overdrive when climbing mountain roads or a mountain pass on the highway. Turning off the overdrive locks up the torque converter and keeps the trans temps cooler.

I think you'll be fine on your trip, but if I were you, I'd drain the coolant, remove the lower radiator hose, and remove the elbow that the thermostat sits behind before you hit the road. I'm betting your jiggle valve is in the 12 O'clock position. Keeping your engine coolant cooler will help with the trans temp since the trans cooler is bathed in the engine coolant.

Here's a video I made of my external cooler install which included replacing the radiator and thermostat. If you go closer to the end of the video, I show you how to remove and replace the thermostat. Good luck with your move, job and new life in Michigan.

<iframe width="560" height="315" src="https://www.youtube.com/embed/2nVbwe2t2T8" frameborder="0" allowfullscreen></iframe>

 

[TRDFerguson]

Thank you for sharing that video. I forgot to mention that if I take the OD off or if the transmission downshifts up a hill, I see a 5-7 degree drop in coolant temp. Thats what made me think that the transmission and coolant temps were so closely related. I thought it was crazy that 1: the transmission fluid temp would change that much due to locking the TC and 2: the coolant temp would react so quickly. I'm glad to hear that you had as much as a 40 degree F difference between the two fluids. When i see my coolant temp change so quickly due to a change in the state of the transmission, it makes me think they are close. But happy to be wrong on this one.

I removed that neck when i replaced the radiator last year in an attempt to get any old coolant out, so if it is installed incorrectly, im the one to blame.

 

[StreetCreeper]

Thank you for sharing that video. I forgot to mention that if I take the OD off or if the transmission downshifts up a hill, I see a 5-7 degree drop in coolant temp. Thats what made me think that the transmission and coolant temps were so closely related. I thought it was crazy that 1: the transmission fluid temp would change that much due to locking the TC and 2: the coolant temp would react so quickly. I'm glad to hear that you had as much as a 40 degree F difference between the two fluids. When i see my coolant temp change so quickly due to a change in the state of the transmission, it makes me think they are close. But happy to be wrong on this one.

I removed that neck when i replaced the radiator last year in an attempt to get any old coolant out, so if it is installed incorrectly, im the one to blame.

Since you replaced everything else, did you check your fan clutch?

 

[Unner]

I'd bet your thermostat is upside down also. Mine runs at 186-190 when fully warmed up. Occasionally 191-193, but never for long periods of time. For the transmission temp since you can't read yours in a 98 with a scangauge I would say just be cautious going up really long inclines. Switch out of OD this way the Torque Converter can lock back up. Temps really climb when it's unlocked in 4th gear, or when you're shifting a lot. With my aftermarket cooler and all my other mods tires, armor etc. I still see transmission temps around 140-150 during the summer on the highway. Since your truck is all stock, or so it appears, and you still have the stock cooling method I'd say you'll be fine, Toyota knew what they were doing temp wise when they designed these. The only reason most of us have an external cooler is to avoid the pink milkshake, but with a new radiator you don't need to worry about that.

I would flip your thermostat though, 216 is a little high for my taste.

 

[jeremyc74]

Thank you for sharing that video. I forgot to mention that if I take the OD off or if the transmission downshifts up a hill, I see a 5-7 degree drop in coolant temp. Thats what made me think that the transmission and coolant temps were so closely related. I thought it was crazy that 1: the transmission fluid temp would change that much due to locking the TC and 2: the coolant temp would react so quickly. I'm glad to hear that you had as much as a 40 degree F difference between the two fluids. When i see my coolant temp change so quickly due to a change in the state of the transmission, it makes me think they are close. But happy to be wrong on this one.

I removed that neck when i replaced the radiator last year in an attempt to get any old coolant out, so if it is installed incorrectly, im the one to blame.

The two are very closely related if you still have the stock cooling setup, but the transmission temp will be lower when you're cruising at a steady state. The torque converter is what generates most of the heat, and it locks up at partial throttle. When you put your foot down and it downshifts, that's when you'll see the coolant temperature fall. That's because the fluid in the transmission is cooler and pulls it down until the thermostat has time to correct.

When you're in traffic or under heavy load they're very close to each other, with the transmission fluid temp going considerably higher at times.

Your coolant temp is above normal for sure. Does it stay at those levels even when you're cruising on the interstate? If it's only doing that around town I'd suspect the fan clutch isn't working properly. If it's staying like that even at interstate speeds I'd suspect the thermostat first, and then the water pump. A clogged radiator could do it too, but you've already replaced that. Something definitely isn't working right.

 

[TRDFerguson]

The two are very closely related if you still have the stock cooling setup, but the transmission temp will be lower when you're cruising at a steady state. The torque converter is what generates most of the heat, and it locks up at partial throttle. When you put your foot down and it downshifts, that's when you'll see the coolant temperature fall. That's because the fluid in the transmission is cooler and pulls it down until the thermostat has time to correct.

When you're in traffic or under heavy load they're very close to each other, with the transmission fluid temp going considerably higher at times.

Your coolant temp is above normal for sure. Does it stay at those levels even when you're cruising on the interstate? If it's only doing that around town I'd suspect the fan clutch isn't working properly. If it's staying like that even at interstate speeds I'd suspect the thermostat first, and then the water pump. A clogged radiator could do it too, but you've already replaced that. Something definitely isn't working right.

The temp stays in the 212-215 range no matter what. Because there is little to no variation in the operating temp, I suspect a functional thermostat that is not set up to work correctly. I arrived in Michigan today, completing my 2400 mile trip and there was no noticeable problems with the transmission. I'll consider myself lucky and consider the transmission fluid toast. A new, correctly installed thermostat and new transmission fluid are in my future.

The sad part is that I just left my college job at Jiffy Lube to come out here to Michigan for my new job.... would love to have access to that T-Tech machine right about now.

 

[4Runnin2000]

Not thread jacking but funny you started this thread as I was just about to Google normal Temps for coolant and transmission. I was driving around today and noticed coolant was over 200 no matter what. But my Trans temps were under 190 constantly(Although it was 117 degrees today so I'm sure that didn't help)Have the stock radiator with 145k miles on it and water pump was changed 40k miles ago when the timing belt was done. I'm hoping a new radiator and thermostat with a flush will help. But subscribed here to see what your outcome is. Here is a snapshot of my temps from my torque app for ish and giggles. Pretty close to the temps you are getting

Sent from my SM-G900V using Tapatalk

 

[Unner]

Not thread jacking but funny you started this thread as I was just about to Google normal Temps for coolant and transmission. I was driving around today and noticed coolant was over 200 no matter what. But my Trans temps were under 190 constantly(Although it was 117 degrees today so I'm sure that didn't help)Have the stock radiator with 145k miles on it and water pump was changed 40k miles ago when the timing belt was done. I'm hoping a new radiator and thermostat with a flush will help. But subscribed here to see what your outcome is. Here is a snapshot of my temps from my torque app for ish and giggles. Pretty close to the temps you are getting

Sent from my SM-G900V using Tapatalk

Your thermostat is almost definitely upside down. My coolant temps were right about there until I flipped it when I did my timing belt. Now it runs 15-20* cooler.

 

[4Runnin2000]

Ok. Yeah I've never heard of the thermostat being flipped like that. A thermostat noob I guess. The previous owner did the timing belt and water pump but it was at the dealer. Maybe they did the thermostat themselves and messed it up. Either way, it will be replaced with a new one shortly and put in the 6 o'clock position now that I know for sure! Sucks to work on the rig in this heat but at the same time I don't want to drive it in this heat for too long without fixing it.

Sent from my SM-G900V using Tapatalk

 

[Arnezie]

Sorry but jiggle valve in the up position is not going to give 216 degree temps alone. I would check the fan clutch if thats good trouble shoot the entire system.