Trans temp gauge help needed

[Tony J.]

Is a gauge that peaks at 250 degrees sufficient, or do I need one that goes up to 280? I need to get one bought and installed soon, so please help if you can!

[ 04-20-2004, 07:03 PM: Message edited by: Tony J. ]

[gmctd]

You should hope your trans temps never get up to 250deg, so yes, the 250* range is better choice.

Most run about 175 - 200* with large external cooler.

[tanker]

Tony I have three Isspro oil temp gauges, engine, trans, rear diff, and they all go to 320*F. I have seen my trans temp hit near 280*F on a long hill converter unlocked. I have it in the trans-cooler line going out to cooler, so that is hot. Depends on the location. smile.gif

[gmctd]

Oops! Sorry about that... ;)

I'd go with Tanker's advise - he's been towing a long time, and you both have the 4L80E, whereas mine is T400 with external od. Difficult to compare the two.

[damork]

I'm running a 250F gauge from a sensor in the pan. I used to see over 210F until I put the biggest cooler I could find in front of the radiator (TruCool by Long Mfg). I don't tow a lot, but on 95F days last year running 75+ I never got above 175F. I don't know what the delta is but was considering adding another sensor in the coverter out line to see what that reads. Anytime ATF climbs much over 200 it will start breaking down, you don't need big pans, just keep what you've got cooled and filtered well.

[Scooby]

Will the test port on the side of a 4L80 give good temp readings?? I have my gage pod installed, but have not brazed a fitting into the trans pan yet. Is there a better/ easier way to sense trans temp ???

[gmctd]

A 'tee' in the line out to the cooler gives an accurate indication of actual operating temperatures.

Caution is required to prevent probe insertion to a depth that blocks full flow thru the 'tee'.

Insert a drill bit of same diameter as 'tee' bore, insert probe.
It should be tight enough to seal when it hits the bit shank.

[CleviteKid]

I use the test port on the driver's side of my 700R4 for the temperature probe, and that was confirmed as a good choice by Don at FOURTH GEAR INC. (http://www.fourthgearinc.com/index.htm)

At this point the pump has picked up hot oil from the pan, heated it some more by pumping it up to pressure, and is just about to send it forward to the cooler(s). This is about the hottest temperature you can find.

Dr. Lee :cool:

[JohnC]

Originally posted by CleviteKid:
At this point the pump has picked up hot oil from the pan, heated it some more by pumping it up to pressure, and is just about to send it forward to the cooler(s). I thought the cooler(s) were on the drain side, before the oil gets to the pan. No? 4L80E different? :confused:

[CleviteKid]

Nuts. Now I have to dig out the factory shop manual and trace out the ATF flow AGAIN. At my advanced age I should learn not to put too much faith in my memory.

But unless and until I prove myself wrong, I do believe that the 700R4 sends the ATF forward after the pump and brings it back cool to be used in the tranny, and heated up by all the activity therein, until it drops back into the pan to do it all over again.

Check back tomorrow. I am now at home, and said manual is at the laboratory.

Dr. Lee :confused:

[CleviteKid]

OK, here is what appears to happen in the 700R4:

The pump draws ATF from the sump, and the line pressure is divided into a "control stream" and a "function stream" (my terms, not GM's).

The "control stream" runs thru all the spool valves in the valve body and obeys the logic controls to apply certain bands and clutches for selecting the appropriate gears. The control stream does NOT run thru the ATF cooler(s).

The "function stream" goes to the Torque Converter Clutch (TCC) spool valve, which is controlled by the TCC solenoid. Uncooled ATF from this stream is used for the pressure to apply or release the TCC, but ATF destined for the torque converter, and for general lubrication of all the bearings, bushings, gears and shafts in the tranny IS sent first to the cooler(s), then off to perform the "function" tasks where friction and fluid shear will generate heat in the ATF. This "function" ATF, after performing the various lubrication and fluid coupling functions, and heating up in the process, then drains to the sump where the whole process starts again.

So, I kinda sorta think I was mostly right; the ATF that is gonna get hotter due to friction is cooled first. ATF that is only gonna provide a reference signal, or apply pressure without frictional heating of the fluid is not cooled first.

A lot of the pressure or control ATF is more or less static at any steady state condition, sort of like when you are stepping on the brake pedal. In the middle of a gradual stop the brake fluid is applying pressure to the calipers and the pads, but is NOT flowing, and is not generating or absorbing any heat from friction in the brake fluid or in parts wetted by the brake fluid.

This makes sense to me, does it resonate for anyone else ? ? ? :confused:

Dr. Lee :cool:

[MTTwister]

so Dr Lee- re the Test Port - which stream is this in , and is this a good tranny temp reference point?

Info only - My probe is already in the test port. I noticed a drip under the truck last night, so I may need to goo-pucky the fittings and pan bolts, but the probe is probably gonna stay there.

[CleviteKid]

I knew I left something out !! The test port is in the "function stream" so it sees a relatively high flow of oil from the pump go past it. Thus it should be representative of the oil temperature being pulled up out of the sump by the pump. There are some further "control stream" bleeds off of the function stream, after the test port, but that does not alter my basic conclusion that the test port IS a good place for a transmission temperature probe.

Dr. Lee :cool:

[JohnC]

OK, I guess I'll have to pull out MY manuals. this is, after all, the 6.5 forum and we ain't got no steenkin' 700R4's here...

:cool:

[CleviteKid]

. . . but . . but . . but, JC, uh . . I'm trying to have it both ways - - -

My engine block was originally a 6.2L, so I claim to belong to the 6.2L crowd . . . but . . uh . . I sorta had Jamie and Benny bore it out to, ya know, like 6.5L dimensions, and stuff it with 6.5L pistons, so it sorta IS a 6.5L . . .

. . . and, uh, I think next you're might be gonna tell me this is the 6.5L Turbo Diesel Forum. Well, uh, I guess that is what it says, but as I have disclosed elsewhere I did use, uh, TurboCAD to design some of the custom parts for my diesel truck, so, uh, it kinda sorta is maybe a TURBO DIESEL :rolleyes: . . .

Now, the next thing you are gonna tell me is that you are a MODERATOR on this here Forum, and I should show some respect . . . so . . . .

Mr. JC, pretty please won't you let me hang around with you big boys and pretend that I am sorta one of the gang? Please ? ? ?

The Clevite Kid ;)

[JohnC]

Originally posted by CleviteKid:
Now, the next thing you are gonna tell me is that you are a MODERATOR on this here Forum, and I should show some respect . . . so . . . .

Where's the fun in that?

OK, so I did some homework last night. What I found makes less sense than all our hypothesizing, at least to me. Seems that in the 4L80E the oil in the pan goes to the pump and then to a distribution valve. Some if the oil goes from there to do all sorts of transmission sorts of things and a portion is diverted to the oil cooler. The output from the cooler is labled "lube" and appears to be directed to two points, fore and aft in the case, where I surmise it "lubes" things. From there I suspect it simply drains back into the pan. So, it seems, we have "bypass cooling" of sorts.

This throws a monkey wrench in my life long conviction that the best place for the temperature sensor is the outlet to the cooler. It would appear that a sesnor in the pan would be at least as good...

[Scooby]

JOHNC--- What about the test port?? I pulled out my manuals last night, started paging thru them, and fell asleep. No lie. Wife comes in about 1 hour later and wakes me up- luckily I didt drool on any of the pages- manual = $$$ !!!
ANYWAY- did you see where the test port is in the system?? I too have 4L80E and would like to put probe in the test port, but I have to pull the pan anyway to change fluid & filter. I'll brazze a fitting in pan if I need to. Thats the way I did my mud truck with the turbo 400. It runs about 180 on the road- and thats with a BIG tranny cooler & fan. When playin in the mud, I'll stop & let it cool when it gets around 240. Unfortunately I believe a lot of the tranny heat I see on it is due to the headers- they dump an enormous amount of heat on either side of the tranny. The 2400 stall converter doesnt help either.

[CleviteKid]

Scooby,

Just 'cause you asked JC, that won't stop me from puttin' my 2 cents in. What JC described seems similar to the 700R4 flow path. The test port does see oil that has just been picked up from the pan, so it will be very close to pan temperature or a bit higher from going thru the pump.

I would recommend you go ahead and put the temperature sensor in the test port, and see if the readings make sense to you. If you don't like it, you can always drop it into a brazed-in pan fitting at your next internal tranny filter change. I predict you will leave the sensor in the test port on your 4L80E.

Dr. Lee :cool:

[gmctd]

I got a EFI 6.5L turbomotor, but I got a 6.2L trans - it's a T400. And it's all in a 6.2L truck. Where do I post? :confused:

I put a probe in the T400 test port, but it consistently read 285 - 325deg, even in winter, so now I have a tee'd probe in both lines, to and from cooler.
Always reads less than 200deg, to. Much lower, from.

Test port has a 1/8" pipe plug, again. :cool:

[CleviteKid]

jd:

You are such a wealth of insight and information that you can post ANYWHERE YOU WANT. If you are in doubt, you have my personal invitation to post in "Ask Dr. Lee" as often as you would like.


Dr. Lee :cool:

[gmctd]

Awwww....shucks, Doc. redface.gif
;)

[tom.mcinerney]

JC:
1-I know nothing about trannys.
2-I spent a sizeable fortune having a 4L80E remanned. The tech explained (attempted) to me lots of things which were 'beyond me'. He also took a minute to describe the cooling oil flow. It is indeed a bypass deal. My confused recollection is that whenever accelerating, there is essentially NO flow to/thru cooler. When coasting, cooling flow is active. He said the justification is to conserve energy(!?!). Full time flow would consume upwards of 30 HP. This might point to an enthusiast's modification for extreme endurance, or hard work racing. Maybe we should check with some of those fellows operating hybrid rigs???