What would cause a 700R4 to run hot?

[DPI]

I have a huge B&M 28,000 cooler on my rig. I burned up one tranny in Moab and installed a new one.

I have two temp sending units one in the return line from the cooler and one in the pressure port. Last night on a test drive, the temp in the pressure port was close to 300* . The unit from the cooler was around 180*.

How much heat will be generated from a convertor not locking up? Will it produce these numbers at hiway speeds?

What else can cause the high temps at hiway speeds, but not at low speeds?

My old tranny had the same kind of temps.

Last question. What electronically will cause a convertor not to lock up, is there a fuse for the lockup? I am thinking there is another issue somewhere in the electronics...

 

[4X4HIGH]

First off the most accurate temp reading will come from the tranny fluid in the pan. If you're only running the B & M cooler without going through the radiator that could also be your troubles. If the convertor is not locking up it will cause high heat. My tranny runs 180* with just the factory cooler in the radiator and the mechanical sender in the pan. When i had my B & M cooler (same one you have) i could never get the trans over 160* even pulling a long steep grade for miles but i also used the radiator cooler in conjunction like you're supposed to do.

 

[DPI]

First off the most accurate temp reading will come from the tranny fluid in the pan. If you're only running the B & M cooler without going through the radiator that could also be your troubles. If the convertor is not locking up it will cause high heat. My tranny runs 180* with just the factory cooler in the radiator and the mechanical sender in the pan. When i had my B & M cooler (same one you have) i could never get the trans over 160* even pulling a long steep grade for miles but i also used the radiator cooler in conjunction like you're supposed to do.

I guess a little more info is due. I am using the B&M cooler after the factory type cooler in the radiator. The radiator is a "heat buster" 4 core model and the motor temp never gets above 170 or so.

The sending units are used to monitor drastic changes in the temperature, not for actual pan fluid measurements. I know about the fluid in the pan giving the most accurate reading, but I went the easier route for now.

My previous tranny never read above 160 coming out of the coolers. And on the hiway it would read below 100 from the cooler, but very high temps in the pressure port. I have heard this port will give in accurate readings, but the temperature of the fluid is still reaching these high temps... That is the important part. Because these high temps is what breaks down the fluid.

Has anyone else installed a temp sending unit in the pressure port? If so, what type of temps did you get?

DP

 

[85mudblazin]

This may not be whats going on but I just had a experience that drove me crazy.

My sender is in the pan and after about 20 minutes of the truck just idiling the temp got up to 250 So I pulled cooler lines making sure I was getting fluid flow, which I was. So then I turned my attention to the guage/sender.

Replaced the sender and it still happened. So I started messing with the guage and it turns out the ground in the guage was loose. Tightened it up and she nevers gets over 150


If it really is getting to 300 , then you would have fluid SHOOTING out of the vent tube, so I think you should first make sure its actually getting to 300.

 

[mrk5]

I guess I'm kinda suspicious about the 300° temp. I say that because I'm surprised that your temp would be 120° different. That seems like one hell of an efficient cooler.

I had a regular tube & fin cooler when I installed temp guage. I didn't like the temps, so I installed a B&M in series after the tube & fin cooler. The B&M dropped my temps 30°.

I have my temp sender in the line going out to the cooler.

If I were you, I would try swapping the guages on the sending units and see if the numbers are the same.

B_to_C has his temp sender in the pressure port and with 40" MTRs and 4.56 gears, his doesn't get as high as 300°.

I also think that converters add heat, especially if they are high stall. I think that's why my TH400 wanted 2 coolers; I have a high stall converter and 400s don't have lock-up.

 

[Hossbaby50]

With the converter not locking up on my 700R4 I have gotten the temps up to about 250*. I did this on the highway trying to sustain 80mph. I slowed down to about 65 and it lowered the strain and the temps started to come down. The sender is spliced into the cooler lines. The converter not locking up is the major cause of heat buildup in the tranny.

My truck has 2 big coolers on it. A 24K cooler and a 16K cooler on my truck. The lines do not run threw the radiator anymore.

If your converter isn't locking up it will generate alot of heat. The TV cable not being adjusted properly can cause the converter to no lockup or having problems with the lockup switch. My truck has problems with the lockup switch. You can bypass the lockup switch with a manual lockup switch. There are details on how to do this on the net somewhere.

Harley

 

[1985_K5_Silverado]

A high stall converter (if you have one) will raise the max operating temp a bit, making an auxiliary cooler worth considering, but wouldn't move the temp in OD with the converter locked up.

 

[Hossbaby50]

I have a low stall converter in my truck. 1000RPM or so roughly.

Harley

 

[jarheadk5]

Last question. What electronically will cause a convertor not to lock up, is there a fuse for the lockup? I am thinking there is another issue somewhere in the electronics...

There is a switch on the brake pedal (might even be the brake light switch...) that causes the T/C to unlock when the brake pedal is pushed. The switch could be out of adjustment, or the wiring might be shorted/broken.

 

[Pookster]

I have 3 coolers for the k5. Its overkill, some say its not reaching "operating temps" to burn off moisture, but I change fluid yearly anyways. first loop goes off radiator, then to a tube and fin cooler, then a stacked plate. Significant temp differences from one cooler to another.

 

[Hossbaby50]

I run 2 stacked plate B&M converters with a combined GVW of about 40,000lbs. I don't run the radiator cooler anymore but I can still get my fluid hot if I am trying to go to fast on the street. I also have a 1 quart external tranny filter on the truck that increases volume of the system by 1 quart.

My normal operating temp is 160-180* pre cooler. I have driven the temp up to 240-250* trying to push OD in non-lockup. When I am crawling my temps never get about 160*.

If my tranny never got about 150* I would be damn happy and would care less about it. I imagine that the TH400 I put in next with those coolers should last forever and never see temps about 200* in its lifetime.

Harley

 

[Alumbaugh]

My in the radiator cooler was partiallly blocked so it appeared to have a flow, but wasn't nearly enough. Burned up the tranny towing a trailer. The repair shop found the cause and almost burned up their flush machine trying to clear it, which never happened. Now have a new radiator (4 core), transmission, and 28,000 lb external tranny cooler.

 

[MattK]

so does anyone know what exactly is ideal?

 

[Hossbaby50]

Ideal as far as what?

Harley

 

[MattK]

Ideal as far as what?

Harley

sorry i was a bit vague there...i mean temperature wise. is there an optimum temperature or is a "cooler is better" thing?

 

[Hossbaby50]

Like many things it is a double edged sword. To hot is VERY bad, to cold is bad but not anywhere near as bad a to hot.

The thing about the tranny being to cool is it won't get hot enough to evaporate water that can condensate in your tranny fluid. I am not an expert but since water boils at 212* then you should NEVER want/need your fluid to get any hotter then that. I personally wouldn't like to see the temps get above 180*. My crawling temp offroad is 160* and I am fine with that. I think as long as you get your tranny fluid in a normal operating temp of 140-180* then you should be fine.

Harley

 

[1985_K5_Silverado]

Another thing about fluid temp is - where is the sending unit? Are you measuring fluid temp in-the-pan? On the way to the cooler? On the way out of the cooler?

Pan temp will tell you how hot the fluid was when it got back from the cooler, and how hot it will be as it gets sucked into the pickip tube, but not how hot it got before it left the transmission (which some would say is much more important number).

 

[Hossbaby50]

Agreed. I have my sensor in the line coming out of the tranny headed to the coolers so the temps I should be getting are when the fluid should be at its hottest point.

Some people don't like cutting into the tranny cooler hardline for the sensor because they can leak. I have had mine setup like that for 4 years with no problems. The compression fittings do a great job at keeping it all sealed up. I think my temp setup was like $50 from B&M including the gauge, sender, couplers, etc. Cheap insurance if you ask me. My last 700R4 cost me $1600 so the $200 that I have sunk into the gauge, external filter, and 2 coolers is well worth the money to keep that tranny alive longer.

Harley

 

[ryoken]

If you're only running the B & M cooler without going through the radiator that could also be your troubles. .

Mind explaining your thought process on this?

 

[4X4HIGH]

Without the radiator cooler the tranny will run too hot in the summer and too cold in the winter and without reaching a temp of about 160-180* the tranny can't burn off any condensation within the fluid and water will kill a tranny.