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Old 01-26-2018, 12:11 PM   #1
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Default Question about my new Scanguage II temp readings

Made my first longer trip since installing a Scanguage II in my 2003 Chevy 6 liter Roadtrek. The 4-speed tranny and 4:10 rear end. Cruises at hwy speeds at between 2200 and 2400 rpm.

Started on on a cool morning, temp in the 40's. The tranny temp (TFT) was running in the mid 130's. Once the sun got up around 11 am the TFT gradually climbed to mid 140's with air temp around 60F. This was all on I-70 crossing Missouri which is mostly flattish, just gentle grades all the way.

Coming home in mid afternoon was pretty similar, TFT never showed anything higher than low 150's. By the time I got home, in the dark, TFT was running in the high 120's with air temp in the low 50's, after about 4 hours of secondary paved road driving with lots of big and small hills.

Now, after all that, do these temps seem low? They do to me, but I don't know where the SGII gets its TFT reading from and what to expect. Thanks, Mike.
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Old 01-26-2018, 01:50 PM   #2
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Those are pretty typical for 40-60* temps. Do you have the optional "trailer towing" package that includes a transmission cooler? You would be able to see it through the grille, near the center, right behind the grille.

There is no thermostat on the transmission cooling, which is actually done in the right hand side radiator tank by the cooling water. That is the cool water, return, side of the radiator so when it is cool out the water there will not be very warm because of the water thermostat being mostly closed to keep the engine warm.

A thermostat can be added to keep the transmission warmer in cold weather, but it is rarely necessary unless you see well below freezing weather a lot. Thermostats are of more benefit if you have the add on transmission cooler, as they can make it run very cool in cold weather.

Most of us have found that the 4 speed transmissions in the Chevies are much more likely to have problems with getting too hot, rather than too cold, especially on steep climbs in 2nd or 3rd gear. Highway driving in 4th gear like you were doing will show the trans running quite cool in most cases because the torque converter is locked up and there is lots of cooling air. You would see the temp come up quickly with some stop and go driving in town, even in the cool weather.

You will see temps higher than the normally recommended 170*F that we have always heard as the best high limit. It has to do where the temp is sensed in the transmission, and the fact they just let them run hotter in these transmissions. Without added cooling, most will see 210-220*, or even more, fairly regularly if you are in hills, traffic, heat. Normally, you won't see the transmission temp go over 200* until the water temp starts to creep up off of the 195* normal temperature, and then they will climb together.

Your 2003 came with Dexron IV transmission fluid, which is non synthetic. GM switched to Dexron VI in 2007, for the van transmissions, which is a full synthetic and said to be safe for about 20* higher temperatures than the Dexron IV. If you are due for a transmission fluid change, it would be a definitely good idea to get the transmission fully flushed and replaced with the Dexron VI.

We have had a lot of discussions on keeping the Chevies cool in the mountains and heat on this forum and most of us have found it isn't particularly easy.
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Old 01-27-2018, 01:15 PM   #3
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Thanks Booster, I was hoping you would weigh in.

Yes, I have both the tranny cooler and the engine oil cooler, so that must have been playing a part. I have little knowledge of typical transmission temps especially on these vans so your comments are very much appreciated.

Regarding changing over to Dextron VI, I was thinking of doing this myself once the nice weather returns. The tranny was serviced about 30K miles ago by the previous owner and the fluid is still pink and clear, so I am not immediately concerned about it. Local Chevy dealer wants about $325 to do a full flush and I like to do my own stuff anyways so right now thats the plan.

I very much appreciate all the work you document here, and am interested to hear more on your shift point/lockup experiment you are doing now and how it affects your transmission.
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Old 01-27-2018, 07:31 PM   #4
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What I did for changing out the trans fluid shortly after the purchase 4-5 years ago was to drop the pan and change the filter and just refill with that amount. Then at each oil change after that I would just drain the trans pan with the drain plug and refill. I did this four times for a total of five drain outs. I figure I'm good to go at this point.

I'm not particularly keen on 100% flush outs, for some weird reason.

My trans and coolant temps would climb quite rapidly in the mountains pulling a one ton trailer. I recently did a preventative replacement on water pump and belt tensioner and replaced the apparently defective fan clutch. The clutch would not engage when the temps went up. The idler pulley and belt were replaced on the last trip as the pulley bearing froze. We'll see how that works out but I noticed the fan being somewhat more engaged so far in the little bit of driving I've done lately. Hopeful.
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