How accurate is the tranny temp gauge?

[SoCalDMAX]

This topic has come up, mostly in the form of "I think my Allison is running a little hot, how do I cool it down?" I always asked myself, "If we can't trust the fuel gauge, and the oil pressure gauge is off by 10 to 60psi, how can we be sure that the tranny temp gauge is accurate?"

The answer is to install a second gauge. I've got the deep pan with Transynd installed. I've installed a temp probe in the rear of the pan, submerged in the fluid. The SPA DG101 gauge reads in 1* increments and I believe it to be accurate as well as precise.

When the factory gauge reads 100*, the SPA reads 85*. 150* on the factory gauge, the SPA reads 125* to 130*. The difference in part may be attributed to differences in probe location. The stock gauge reads a probe deep in the tranny, I'm picking up the pan temp, more or less. I believe the factory probe is very accurate, but the gauge is cheap and uncalibrated. The fact is, fluid temp appears to be an avg of 20* cooler than indicated. This is on mine, I obviously can't speak for all. This is also based on just a couple of days driving. The probe has been there for months, I just recently completed the wiring and switch install. There's also a probe in my Mag-Hytec diff cover, more on that later.

I hope this helps some of you rest a little easier, I'm beginning to think my tranny's running a bit too cool at times, it takes a while to even get up to an indicated 150*... ;)

Regards, Steve

[Maverick]

I think the factory gauges are very inconsistant. I can push the GMC real hard with a load and the tranny will run 150 all day. Do the same thing with the Chevy and it will climb 190-195. The Chevy is very sensitve as to wether I have T/H on or not. The Chevy will build alot of heat pulling if not in T/H. Usually runs cool in T/H being the TC is locked. Doesn't matter with the GMC runs 150 most of the time. I have gotten it up to 200 once so I know it works up to that far.

[battmain]

SoCal, curious as to the diff temps loaded and unloaded.

[deerhunter7]

Iv'e never tested it against another but if the oil is 20 degrees cooler than shown that is a little save guard. Better than running hotter than
shown.. tongue.gif

[Redhawk]

The stock probe sounds like it is in the right place, so is it possible to use the output of the stock probe and use it to power an aftermarket gauge? It might be an interesting experiment.

[mdrag]

SoCalDMAX,

Me thinks you need two more tranny temp gauges - one in the TO COOLER and another in the FROM COOLER lines smile.gif ;)

[SoCalDMAX]

Yeah, if I had a 6 bay garage with a hydraulic lift, I'd think the same thing too... :D (Sorry that's the 2 pitchers of beer talking... :D )

OK, seriously, I've had very little time to play with the temps, haven't gotten any higher than 150* so far. I'm in VA right now, so when I get back I'll be able to fill in more info as more miles roll up. I do have an IR temp gun, I could shoot the cooler line temps with that and bounce those against the gauge readings. No idea how accurate they'd be, but it would be interesting. I'm also tempted to plumb in a temp probe into the coolant system somewhere just to see... gauges that never move make me nervous.... The problem is, where's the right place to put it? Like your question infers, how efficient is the cooling, and the problem is when one asks what temp is the tranny or whatever, the answer is: where do you want to measure the temp?

I'm still struggling with the difference in EGT readings from 1/8" to 1/4" probe. Same engine, etc, but the thin probe reads 1400*, the 1/4" probe reads 1070* max. I realize the time lag between the 2, the thicker one responds a little slower, but it does respond, it should eventually equalize over the course of a minute or two. This leads me to the question: is the gas temp really what we're interested in or is it the highest temp of any of the exhaust components? If so, then I'm guessing the 1/4" probe is responding more in line with components such as valves, turbo vanes, etc.

That's the problem with talking about EGTs or any temp. Different people are going to get different numbers based on probe location, probe design, gauge accuracy and brand, etc. Any diesel experts want to chime in?

Regards, Steve

[mdrag]

SoCalDMAX,

"I do have an IR temp gun, I could shoot the cooler line temps with that and bounce those against the gauge readings."

I'll volunteer to drive while you take the temp measurements :D

Interesting disparity between the 1/8" vs. 1/4" probes. I know when I check the stored MAX TEMP on my SPA DG-111 (1/8" probe) - I'm often surprised at the number because I've never seen the peak temp (or near the peak temp) displayed on the gauge. I agree with you that for our purposes, the thicker probe would probably be better...Unfortunately, there is no way to verify the accuracy of either probe.

mdrag

[ 10-08-2002: Message edited by: mdrag ]</p>

[mackin]

Socal

Yes, to all the above.......By the time your done you'll have probes to check your probes to check your probes...And gauges to check them gauges to check them gauges......Soon you'll look like that Wally world special with more gadgets then a Mexican tag sale......Where is that PIC, MDRAG seen it before,Red interior........

Your given me a head ache drink more beer and forget it !!!!!!!
Your on the verge of OCD ......... tongue.gif

MAC

[SoCalDMAX]

But you guys keep asking questions!

I figure if John Kennedy answers the hardcore performance questions, SteveO answers the tranny questions, Mdrag answers the accessories/big wheel questions, Hoot keeps all of the Ford owners in line, NutNButGMC answers all of the minivan questions, and you answer all of the law enforcement/DMV points questions ;) , that only leaves me to answer... how hot is this thing getting, anyways?

After spending what I did on the gauges, a few extra senders maximizes the investment. Stay tuned, when I install a boost sensor in the fuel line and try to answer the age old question: How hard is it for the fuel pump to get fuel thru the filter, anyway? :D

Working on pitcher #3, Steve

[77TransAm]

SoCalDMAX, there's been a lot of testing done with a lot more thermocouples than most people have access to.... How about probes for sump temp, to cooler at the trans, to cooler at the cooler, from cooler at the cooler, from cooler at the trans, ambient air temp at each of those areas, and water temp into and out of the radiator (plus pressure drop across the filter and across the cooler circuit, as well as flow through the cooler circuit).

What that has shown is that the cooler lines don't transfer any noticeable amount of heat - there's just too much fluid moving too fast for it to have time to either pick up or shed any heat through the lines. You should be able to put your cooler line probe anywhere in the line that's easily accesible and still get a good reading.

The best way to install a probe is to use a 5/8" compression union. Drill and tap the center part of the union for your thermocouple fitting and then just cut your cooler line where you want the probe. Install the union, run the wire, and you're set!

BTW, the hottest temp you'll see is the converter out, which can be measured in the "To Cooler" line.