Transmission running too cold?
 

Hello everyone, I have a somewhat unusual question. If you haven't figured out by the title, I am concerned that my 2005 Honda Civic's transmission might be running too cold. I installed a Hayden 679 transmission oil cooler (the biggest one I could find, rated at 30,000 pounds) when I installed my Mishimoto racing radiator 5 years ago. The transmission oil cooler seems to work very well, and I am concerned that my transmission may not be warming up enough.

I don't have a trans temp gauge (although I will probably install one eventually) and my trans has no temp sensor, so I rigged a thermometer as a test. I used a small hose clamp to attach my Klein multimeter's thermometer to the oil cooling pipe coming out of the transmission going to the cooler (the hot one) and I set up the multimeter inside the car to monitor trans temp while I drive.

I am actually surprised at how cool the transmission runs with my setup. Today was a cool day for Memphis (only about 80 degrees). The highest temperature I saw was around 135 degrees, and that was while I was pushing it up a pretty steep hill with the converter unlocked. The temp was around 115 degrees most of the time while cruising down the highway with the converter unlocked, and if I unlocked the converter the trans ran at around 120 to 125 degrees on the highway.

So I am wondering if this is too cold, or if this is a good temp to run at. I am pretty sure it is harmless to the transmission since my old trans lasted to 243K miles with good maintenance and this cooler, but I imagine MPG may suffer slightly from running so cold all the time, especially in the winter.

I can get various thermostats to control the trans temp. Most seem to open at around 180 degrees, although some are higher or lower. However, I would rather not install a thermostat unless I need to because I don't want to add another point of failure. If the thermostat were to stick closed and I didn't know it, the trans could quickly be destroyed.

So what do you think about my low trans fluid temperature? Is it harmful to the transmission, and how much would you expect for this to affect gas mileage? Thank you very much in advance!

Is the pipe metal or rubber? Rubber is a good insulator, which would give you a false low.

I would expect the temperature to be closer to what the engine operating temperature is, because the engine is heating up the coolant.

135 sounds kind of low. I'm not sure what the norm is though; the AW4 transmission that my Jeep has is known for running hot.

Edit: I misread what you said. I did not know it is an oil cooler. 135 seems low still.

Why would a hypermiler need a trans cooler that's bigger than stock? Even those of us in the hottest climates struggle for temp.

good reason to stick with the cooler line running through the radiator...well, assuming the radiator is ever up to temp, which it never is...

Ok, good reason to run the oil cooling lines through the hot side of the cooling system.

Great info, thank you. I clamped the thermometer to the metal part of the pipe, so I think I should be getting a fairly accurate reading.

My main focus wasn't gas mileage, it was performance and longevity. The racing radiator that I installed had no built in trans oil cooler. I used to live in Asheville, so climbing long, steep mountains in hot weather was a daily occurrence, I didn't go easy on it while climbing, I added probably 30-40 HP over what this car had stock, I used to occasionally pull a "small" trailer (although sometimes I overloaded it pretty bad, the trailer was about 2500 pounds when I moved to Memphis. Oops.) And sometimes I push it hard, like flooring it from a stop.

My racing radiator has no trans oil cooler. And even if it did I don't know how much heat it would actually add to the fluid being on the cold side of the rad. Probably not much, it may even cool the fluid in the winter when the thermostat isn't open much or at all.

I would say yes just because you want the oil to thin out to spec. If its too cool, it is just causing extra friction and a slight loss in mpg.
I assume this car is an automatic?

Thank you for your help. Yes, it's an auto. How many MPG do you suspect I may be giving up by running the trans this cold? I would guess no more than 1 MPG, but I'm not sure

For what it's worth, GM trucks let you see trans temp from the cluster, the '12 2500 at work (6.0 iron block and 6speed) runs around 160-170°F. Our Yukon hybrid (6.0 aluminum block, very similar to LS2, with 2ML70 4 speed) also runs about 160-170°F.

Not a ton. From class we had a little tribology portion in mechanical system design and the big weights weren't hugely different. I'm sure you could find a "temp and viscosity thickness" chart and compare different weights at x temp for your reference as it relates to your transmission. Main take away: gas mileage will only vary a small percent wise, but the friction goes up and decreases the life cycle rating if the bearing/wear tolerances are designed to maintain a certain gap /psi rating with the spec weight at x temperature and you put in a thicc er fluid or cool the fluid too much. Think: Toyota doesn't recommend 0w-20 in their 0w-16 designed motors.

Thanks. So you are saying that running this cold may actually be harmful to the transmission?

reiterate: No probably not. I don't actually know what the spec for ATF would be in your application, but you will lose a couple percent in FE since you're a couple degrees colder than optimal.

I would just plug your lines, and run a test loop with and without and see what the difference was. I used to have a 5 mile test loop I used on the mustang.

Thanks again, I really appreciate your help. I have heard that the torque converter stall speed increases as the oil temp increases because the thinner oil flows through the torque converter easier. Is there any truth to that?

EDIT: Now that I think about it, I could test how stall speed changes with oil temperature pretty easily: Warm up the engine to operating temp, warm the trans up to ~200 degrees, test the stall speed (press the brake, put trans in D, floor it briefly, and see what RPM the engine will rev to). Then cool the trans off to ~100 degrees by spraying the cooler with water while the engine is running until it cools off, and retest stall speed to see how much it changes, if at all. If 100 degrees of oil temp difference doesn't measurably affect stall speed, the difference is certainly negligible.

How about a thermostat?
https://derale.com/product-footer/fl...ol-thermostats

I edited my post above.

So I had the opportunity to drive the Yukon a couple times the last couple days, temps in the low 90's and the trans stayed at 165, not 180.

I would guess 130°F is fine, maybe a little low but from my limited research anything 110 to 180 seems to be acceptable or normal.

I was wondering about getting one. However, I would prefer to not get one if it would be of no benefit. Like I said before, I worry about the thermostat sticking closed and overheating the trans. But if I install a trans temp gauge I could watch the temperature and make sure it stays normal.

I have an update. I discovered that I can not trust my temp readings because my thermometer seems to read cold, at least sometimes. I was idling in neutral for about 3 minutes at a railroad track, and the thermometer dropped to about 90 degrees F, which was about 5 degrees below ambient temp. Not possible. So once I got home (about 30 seconds later) I felt the pipe that I mounted my temp sensor to, and it was hot even though the thermometer showed ~90 degrees. The thermometer was still securely clamped to the pipe. I would guess that the pipe was at least 120 degrees, probably more, so I am going to install a real trans temp gauge.

I tested my stall speed cold (~90 degrees F) vs hot (~180 degrees F) and the difference in my stall speed was about 50 RPM. (2650 vs 2700 RPM respectively). I was expecting more of a difference, but now I know :)

Trans oil likes to be warm, not hot. My temps are ~140 when warmed up. It's fine.

FWIW,, ATF is usually viscosity stable in a pretty wide range,,

In a tow vehicle they usually recommend keeping the auto under
220. few auto lubricants like to be any hotter.

I believe the redline website used to have a table for proper temps,,

Redline ATF, with no cooler lowers my transfercase temp about 40 degrees on my jeep when in low range working it hard.

I think its as important to keep the temp consistent as it is to keep it low.
Thermal changes work the parts harder..

I installed a temp gauge about a month ago and the transmission frequently doesn't even reach 100 degrees in cooler weather. I was cruising down the highway with the converter locked in about 30 degree weather and the trans temp was running a 75-80 degrees F. Is this bad for the trans? And if not, how bad is it for fuel efficiency? Thanks

75-80 should be fine. I don't have a temp gauge but I do have a BIG cooler on the rav4 and they are definitely down. A bit less mileage this year with the cooler, but it shifts better and since I plow with it, that's ok.

Thanks. My trans seems to shift about the same regardless of temp, it shifts hard either way with the solenoid mods I did. Just curious how much worse your mileage is? I can't imagine that I'm losing more than 1 MPG from running the trans a bit cold, but I could be wrong. Thanks

About 1 mpg is what I figure.

MPG loss at the expensive of a LONGER life transmission


gas is cheap you would only lose like 1% while extending the life of the transmission for many many extra miles

mine runs between 145F-165F winter/summer those are the ideal temps if you want the transmission to last 300,000-400,000 miles


once you get into the 190-210F range it will last about 115-150k miles

Big maybe. Bearing gaps actually desire a specific weight. Not higher or lower.

I would say that's an unfair relation, your transmission has no torque converter which is where the vast majority of transmission heat is generated.

I'm not so sure about that. Most transmissions (including mine) don't come with a thermostat to keep it at a specific temperature, it actually varies a lot depending on outside temp. I know most people say that the cooler in the radiator regulates the temp and warms the fluid up, but that's not true. The cooler is in the cold side of the radiator, which doesn't even start to warm up until the thermostat opens, and can actually stay pretty cold on cool days when the thermostat isn't open much.
Some newer transmissions actually run the fluid through the hot side of the cooling system to help warm it up.

So I am pretty much thinking if the engineers weren't worried about the transmission failing from running cold I shouldn't be either, but if you have different thoughts on this please let me know.

the most stress is on the front Sun gear and input/out shaft there is a risk every time it 'starts' the it will blow apart :eek:


someone seized an engine and ended up blowing apart the transmission along with it.. i asked them why they did not have it towed , they did not say anything :confused:


it does have two 60kw electrical motors that need to be cooled to make up for it


it also comes with the heavy duty tow package ( for the cooling only since the max is 6200 pounds for 2wd )

Speaking of towing, we pulled a uhaul 4x8 with about 800 lbs in it, cabin filled to the bursting point, along with two bicycles mounted on the roof at up to 85mph cruising and the trans never went over 171°F. So yes, the cooling is quite good!

yeah make sure Not to use the Revise gear when towing (just don't put yourself in that situation )

you will damage the CVT revise gear also use the M gear m3 if you want AFM M4 give you full power V8 with E-Assist (besure to turn on the A/C so you don't accidentally deep CYCLE the high voltage battery i.e getting the State of charge too high) it will be worth the slight extra gas :D
as that HV battery is expensive.... so also good to use the A/C in the winter occasionally for 5min or so (this will keep the seals in good condition for many many years )


if you can afford it get 91/93 octane for the MAX amount of MPG and MAX low end power i get about 27mpg on the highway with it worth the extra 30 cents as 87 octane would cost me over 5$ to go 27 miles
i save 1.34 per gallon with the high octane fuel chevron or mobil are the best as they don't screw you on the octane you buy Shell/arco have screwed me on the octane when I paid for 91 octane they gave me 87 octane it happened at 3 stations for both arco and shell. what a scam they are pulling

I left it in drive and only put it in m4 when we were coming down the mountains. And yes, using premium fuel kept it from downshifting as much, spent a lot of time in a lower gear ratio, hard to tell which one with this trans.

Revise gear?

Sorry for the thread jack!

reverse gear my bad it's bad to back up with a load on the cvt gear

dont' use drive gear when towing unless your above 45mph, so you can stay out of 6th gear [EVT2], then you can switch from M4 to Drive, you can cause severe damage to the CVT portion if you tow in CVT mode but it's your transmission

it's easy to tell
0-15MPH 1st
0-29 mph 5th gear[EVT1] [Auto Stop]
15-35 2nd
35-50 3rd gear
40-45mph 6th gear[EVT2 v4-DFCO 50MPH and below, Fuel economy mode]
55mph > 4th Gear [50-55 varies between 3rd and 4th gear depending on engine load]

as you can see the gearing is complicated



4th gear is good tell 90mph it will be about 2300 rpm at that speed


it's hard to tell but i go by the RPM (shifts are smooth a silk and physically undetectable)

I think you are confusing a CVT with a DCT. Most CVT transmissions use a torque converter (a fluid coupling) like a regular auto instead of a clutch, so they aren't harmed by crawling forwards or backwards. However, some CVTs like the ones found in some Hondas use a start clutch instead of a torque converter, so it's best to avoid crawling in those just like with a DCT.

A DCT (Dual clutch transmission) has no torque converter. Instead, it has clutches that may overheat from slipping and fail if you crawl for a long time, especially under load. The reason for this is because it can't fully engage the clutches until you reach a certain speed or the engine would stall (like letting the clutch out at too low of a speed in a manual transmission). Therefore, the clutches must slip. This quickly makes a lot of heat, which can destroy the clutches if done repetitively or for extended periods of time, especially under load.

Gm says it's a CVT or as they call it a EVT

Continuous Electric Ratio Hybrid Transmission With 4 Fixed Gears.


Gear Ratios
1st — 3.69:1
2nd — 1.70:1
3rd — 1.00:1
4th — 0.73:1
EVT #1 — Infinity to 1.70:1
EVT #2 — 1.70 to 0.50:1
Reverse — Infinity to 1.70:1

Here's an interesting idea- a CVT that the driver can set what the fixed ratios are and paddle shift it. That would be pretty fun in my opinion

you know how Toyota claimed they had a "first" CVT with a first gear launch
https://www.fuelsandlubes.com/toyota...t-launch-gear/



well GM beat them too it with a 4 SPEED launch back in 2008... :thumbup:

i think toyota still grappling with the pickle matrix. and did not notice a CVT with a 4 speed transmission was all ready on the market..

basically they reinvented the two mode

I wonder how bad it is to tow with the cvt in the Prius. I pull a 1000lb boat from 90k to 160k now lol.

I'd probably add that the GM/BMW/Chrysler hybrid system is quite different. They have 6 different operating modes where the Toyota just starts in first then swaps to the CVT to shift the efficiency band up to the range where most of us do all of our driving. The trios group engineering effort was to create more torque with a smaller electric drive system for SUVs as the main goal.

Trans temp?
 

With my 6sp(7 counting TC lockup) Allison, 145°f to enter learning mode. Per the Trans Builder keep it above 145°f to keep it alive and adjusting the shift trims for current conditions.

Dodge put out a TSB about transmission fluid viscosity issues. At -10 F the ATF+4 trans fluid congeals/ freezes in the air to liquid cooler mounted in the cooling stack, restricting flow through the cooler circuit causing the transmission to overheat.
I have not gotten a straight answer at what temp this is a problem with Allison fluid. Dodges fix was to bypass the air unit and just use the massave remote liquid the liquid unit bolted to the side of the block using a heater core circuit. And tell the customer to swap back and forth for towing in hot and solo in cold.

Final advice I implemented routing.
Stock is:
Trans/water/air/trans

Recommended:
Trans/air/water/trans

Reasons:
Industrial Allison standalone computer locks the TC@ 20mph ~1/2 way through 2nd. So no TC heat, it will(my Allison) run too cold and seldom be in learning mode especially in MT winter. So far single digits trans temp 161° F/ CT,171. Without pulling heat from the Cummins the Allison would not be happy. And the worst of winter is yet to come.

Find out what temp your TCM enables learning. That is the magic low temp, bottom line.
If it is all hydraulic mechanical so long as it's not overheated it doesn't care . However the TCM from the 46RH that came out did disable the electrohydraulic OD (.61/2.44 final) till the trans hit 45°f ~1.5 mi @ -20F when pluged in CT ~60°F

---
+1 on the user selectable raito and #of shifts available CVT shift patterns. I still dont get the point of a CVT with set shift raitos , especially it described here to match a normal automatic . Only thing I can come up with is too many complaints about people feeling like they're driving a snowmobile with three RPMs accelerating, cruising, and compression braking.