ATF Temperatures and Cooling System Performance - Second Generation Nissan Xterra Forums (2005+)
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post #1 of 77 (permalink) Old 07-03-2010, 10:07 AM Thread Starter
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ATF Temperatures and Cooling System Performance

Since there were few new developments after making on road mesurements I decided to start a new thread on this topic.

Last summer I noticed that during certain trail conditions that the engine would stall against the converter. This has to raise the ATF temperature. I was interested in measuring the temperature of the fluid out of the trans and also the effectiveness of the two coolers.

I made a series of temperature measurements at trans outlet, the air-atf inlet, the air-atf outlet, and the trans inlet. The thermocouples are bare bead Type K. I split a 3/8Ē piece of fuel line to slip over the tubing into and out of the trans, inserted the TC between the hose and tubing, and used a worm type clamp to tighten the hose and ensure intimate contact between the TC and the tubing. At the air-atf cooler I inserted the TC between the hose and the cooler at the inlet side or the outlet side. There are only three TCs at this time so one of the TCs was attached at either the inlet or the outlet of the air-atf cooler.

The Fluke meter used to measure the TC output is a dual channel so only two of the three can be monitored at a given time. This isnít a real issue for me, it will just take longer to collect enough data to understand the performance of the system. The meter can sample and store the max, min, and average readings for both channels and the difference for any duration of time.

I zip tied an indoor/outdoor thermometer sensor tip to the grill to measure the outside temperature. It was placed at the back so it isnít in the sun.

When I first started making measurements while driving it became apparent the system is more complicated than first thought. I had assumed the steel tubing had minimal heat transfer during use, a error on my part. After reaching a nominal trans operating temperature, the temperature at the trans inlet was hotter than the air-atf inlet. It turns out there are four heat exchangers in the system, the steel tubing out of the trans, the rad-atf cooler, the air-atf cooler, and the steel return line.

At this time I havenít been able to measure the temperature at the outlet of the steel tubing to the rad cooler. The measurements to date have been at the inlet of the air-atf cooler which is the temperature drop for both the steel outlet tube and the rad-atf cooler.

Measurements were made in ambient temperatures of 68F to 98F. Some were done taking snapshot readings while driving. Other times the meter was set to the max-min-avg setting and reviewed after 30 minutes or more to get time averaged data. The TC attachment method was very sensitive to changing load conditions, as soon as the converter would unlock the observed temperature would increase. I think that the measurements are not much different from the atf temperature.

To simplify the text, Iím using the following abbreviations.
Tout - temperature at the trans outlet on the steel feed line
Trad - temperature at outlet of the rad-atf cooler, measured at the air-atf cooler inlet
Tair - temperature at the outlet of the air-atf cooler
Tin - temperature at the inlet to the trans on the steel return line

What happened and my interpretation of the measurements.

1. There was no evidence of the rad-atf cooler heating the atf. On three cold starts Trad was always colder than Tout as the engine and trans warmed up. As the trans warmed up the difference became larger. The difference is few degrees when the Tout is mid 90s and 13-14F when Tout is about 120F. It takes about 20 minutes for the Tout to reach about 150F with normal highway driving when the air temp is about 75F.

2. The atf is heated in the return line to the transmission. From a cold start and during all operation the atf is absorbing heat. On one cold start at 75F ambient driving about 65mph, after 3 minutes Tout was 108F, Tair was 99, and Tin was 104. At 10 minutes, Tout was 131F, Tair was 111, and Tin was 124. At 20 minutes, Tout was 147F, Tair was 121, and Tin was 137. I suspect some of the heat is from the steel outlet line. The two lines are tightly clamped together. Without making a few additional measurements it is just a guess.

3. After warming up and driving on the highway at 65 to 70mph, Tout varied from 145F to 205F. The average or nominal was about 155F over a temperature range of 68F to 98 F. Tin during the same conditions varied from a max of about 145F, min of 130F, and a nominal of about 137F. The highest Tout was climbing a steep grade at 55mph in 95F ambient temperature. As soon as cresting the pass the temperatures started dropping.

4. At highway speeds difference between Tout and Trad was a max of about 30F, a min of 15F, and a nominal of about 20F. This difference is the sum of any heat loss from the steel tube and the rad-atf cooler. The temperature drop from the air-atf cooler is a max of about 25F, a min of about 8F, and a nominal of about 15F. The air-atf temperature drop is a estimate from the other measurements, I didnít have the capability to directly measure the temperature.

5. Driving on gravel roads and 4WD trails the atf temperatures are higher. The slower the speeds and the higher the load, the higher the temperatures. Tout ranges from 170F to 200F and Tin ranges from 150F to 180F. Higher slippage in the torque converter creates more heat and lower air flow doesnít cool as effectively. Driving during high ambient temperatures reduces the cooling.

6. Off-road, the temperature drop from Tout to Trad was about the same as highway driving. This isnít surprising since the heat exchanger isnít too dependent on air flow from vehicle speed as long as the cooling fans are working properly.

7. Off-road, the air-atf cooler works well at about 30 mph but the efficiency falls off at 10-15mph. The temperature drop is in the range of 5F to 15F.

Iím comfortable with the OEM cooling system performance. The brief periods where the Tout is in the 190-200F range isnít enough to cause significant degradation. I plan on flushing the trans on a regular schedule so trans life shouldnít be an issue for me from high atf temperatures.

Those who are bypassing the rad-atf cooler should consider this data. The rad cooler is an effective heat exchanger at low speeds when heat generation in the trans is high. I recognize the temperature drop measured at the rad-atf outlet is the drop across both the steel feed line and the rad cooler. High atf temperatures wonít kill a trans suddenly, they slowly degrade the performance over time. The atf will degrade and the seals in the trans can harden and leak.

Adding a fan to the OEM cooler would increase itís efficiency especially at low vehicle speeds.

Backing up two air-fluid heat exchangers reduces the efficiency, the airflow through is reduced by the added thickness. Plus the heated air from the first exchanger is moving over the second exchanger, reducing delta T across the second. There is a reason the OEM cooler is positioned in front of the AC condensing coil, and itís not so there is space for a second cooler.

I may get some additional TCs to monitor the temperature at the outlet of the steel feed line, the inlet to the air-atf cooler, and the air temperature in the volume around the steel atf lines. The information in needed for me to make a decision about the effectiveness of the factory system, Iíve already done that, I am just curious about how the system functions.

Jeff
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post #2 of 77 (permalink) Old 07-03-2010, 12:59 PM
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So adding a second cooler right behind the first is actually bad? I just did this...would I have been better off adding a fan instead then?
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post #3 of 77 (permalink) Old 07-03-2010, 02:44 PM Thread Starter
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I wouldn't say that's it's bad, just not the best spot. Probably better than not adding the second cooler. A better spot would be on the left(drivers) side in clear air.

Personally, if I was going to do the rad bypass I would add a second cooler and add a fan to at least one on them for low speed cooling.

Jeff

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post #4 of 77 (permalink) Old 07-03-2010, 03:24 PM
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VERY valuable information. Thank you!!
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post #5 of 77 (permalink) Old 07-03-2010, 08:59 PM
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Quote:
Originally Posted by jeff_redx View Post

I made a series of temperature measurements at trans outlet, the air-atf inlet, the air-atf outlet, and the trans inlet.

The air-atf temperature drop is a estimate from the other measurements, I didnít have the capability to directly measure the temperature.


Jeff
Jeff - just for my sanity, I'm reading this several times just to understand - I snipped these two sections out of your procedure and then your observations. Looks like at one point you had TC's on inlet & outlet of the air-atf cooler. Why didn't you have the capability to directly measure the temperature and provided an estimate?
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post #6 of 77 (permalink) Old 07-03-2010, 11:19 PM Thread Starter
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Quote:
Originally Posted by brett View Post
Jeff - just for my sanity, I'm reading this several times just to understand - I snipped these two sections out of your procedure and then your observations. Looks like at one point you had TC's on inlet & outlet of the air-atf cooler. Why didn't you have the capability to directly measure the temperature and provided an estimate?
Brett,

There were only three TCs. The two attached to the steel feed and return lines at the trans outlet and inlet are difficult to remove, or reattach. I wasn't anxious to crawl under a hot car in 95F heat.

The third TC could be easily switched from the inlet or outlet of the air-atf cooler by removing the bumper cover, even on a hot car. But only one point at a time could be measured.

I've ordered some extra TCs to be able to measure the rad-atf cooler inlet and both air-atf inlet and outlet.

Jeff

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post #7 of 77 (permalink) Old 07-04-2010, 12:24 PM
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Well, I am continually impressed that you do all of what you do with one good hand. Doesn't seem to slow you down at all.
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post #8 of 77 (permalink) Old 07-16-2010, 09:53 PM Thread Starter
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Updated information.

I added additional thermocouples and have the Omega data logger to record the data, one nice feature is the data is real time stamped. There are now 8 thermocouples. There is an indoor/outdoor thermometer used for measuring the temperature of the air entering the grill.

1. Trans out, start of the steel feed line.
2. Rad-ATF cooler inlet, also the end of the steel feed line.
3. Rad-ATF cooler outlet, also the Air-ATF cooler inlet.
4. Air-ATF cooler outlet, also the inlet to the steel return line.
5. Return inlet, beginning of the steel return line.
6. Trans in 1, about 6 inches in front of the return line fitting.
7. Trans in, end of the steel return line.
8. Ambient front, engine bay at the front of the steel ATF lines.
9. Ambient mid, engine bay at middle by steel lines.
10. Ambient back, about 6 inches by the steel line fittings on trans.
11. Inlet to engine thermostat housing, feed from the lower radiator header where the Rad-ATF cooler is located. TC between the lower radiator hose and housing nipple.
12. ATF pan, ATF temperature measured in pan through dipstick tube.





The logger is only four channels so not every one can be recorded. The first time I did a cold start log with the trans out, rad-atf inlet, air-atf outlet, and trans in TCs. This was to get some feeling for the temperature change in the line during heating and hot-operation. The ambient temperature was about 85F for the short drive of about 9 minutes on city streets at about 40 mph. Nothing unusual was observed, the atf heated with temperature peaks from sitting at lights and slower heating with easy driving. The difference between the rad-atf inlet and air-atf outlet is the sum of the temperature difference for both coolers so no conclusion could be drawn about the radiator coolant heating the atf fluid from this log. It appears the there is more heating in the return line than cooling in the feed line as the engine and transmission heat up. A possible conclusion is there isnít much transfer between the two lines.



A second log was made when hot at speeds of about 40 mph with the ambient temperature 95F to 99F. The peaks and valleys correspond to sitting at lights and steady driving. The heat loss in the feed line is much lower than the heat gain in the return line. The engine bay ambient temperatures havenít been measured yet.



Next day log used the thermostat housing or rad coolant, rad-atf in, rad-atf out, and air-atf out TCs. Cold start at about 35 mph.. The temperature of the thermostat housing increased rapidly until the thermostat opened and the coolant started to flow into the housing with the observable temperature drop. Given the thickness of the casting I would expect this temperature measurement to be the least reliable, though it is probably higher than the coolant temperature. From the start the temperature drop in the rad-atf cooler was measurable, no evidence of any heating. Given the low speed and the low atf temperature there wasnít much cooling in the air-atf cooler.



The next log was about two hours after the end of the previous log with the shut off. The log was divided into two consecutive plots. Ambient temperature was 95F to 99F. The first plot was at driving speeds of 35 - 40mph. The thermostat was closed at the start and then opened and behaved predictably. As the atf heated both coolers became more effective. The rad-atf cooler had a larger temperature drop than the air-atf cooler, especially at lower vehicle speeds.



The second part of the log was at higher speeds of 50 - 60 mph on level to slight downhill grades. The rad- atf cooler was still more effective than the air-atf. Up to the higher speed the converter was probably not locked very much because the traffic conditions. The temperature drop in both the atf and the coolant was dramatic. The reduced cooling from the air-atf cooler at lower speeds is very reproducible and expected.



There was one more log of hot start and a few short trips with brief engine off periods, 96F - 99F ambient and speeds of 35 - 40mph. The logger was left on during the engine off periods. Nothing surprising but interesting how quickly the temperature at the housing drops when coolant starts to flow.



Iím planning on doing similar logs on our upcoming trip to Ouray in a few weeks with off road trips planned. The temperatures should be lower. I also have a trip planned to Page, AZ, in mid August when temperatures should be in the 90s. More data to come.

Jeff
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Last edited by jeff_redx; 08-07-2010 at 12:49 PM.
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post #9 of 77 (permalink) Old 07-19-2010, 10:32 AM Thread Starter
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Judging interest in temperature data

The new data was posted two days ago and there haven't been any responses. If anyone is still interested in seeing this type of data in the future please let me know. It takes time and effort to prepare it for posting and it's time well spent if it is of value. If members aren't interested I don't have a reason to keep posting this information.

Thanks,
Jeff

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post #10 of 77 (permalink) Old 07-19-2010, 10:58 AM
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Jeff this is awesome data. It is very interesting to see how effective the Rad-ATF cooler is at low speed cooling. Given that I drive my truck offroad often I will be adding a fan to one of the Trans coolers to keep the tranny nice and cool. Thank you. I know it is a lot of hard work to prepare data in a form that everyone can understand like you have! It is also very interesting to see the temperature fluctuations caused by stop and go compared with driving that has constant airflow across the coolers.




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