jtmarten

I took my '96 K2500 to the dealer to have the intake gaskets replaced. They replaced the thermostat as well, and she runs much hotter now, usually right at/below the 210 mark, so I'm assuming they installed a 195* t-stat. Previously she ran much cooler. The added temp caused some problems this weekend with the tranny. I drove from Colo Springs to Detroit to pick up my new boat and had no issues. After picking up the boat I started having trouble with losing OD. I'd stop for gas and get OD back after just a few minutes of cooling. Ended up having to run at 55 instead of 65 and was able to keep it cool enough to finish the trip without problems. Boy was Sammy Hagar right! Driving 55 sucks! Fluid level was fine, no bubbles on dipstick indicating boiling, fluid a nice pink/light red.

What are the best options for cooler t-stats? 180, 160? I'm leaning towards a 160, which I think it had before. That'll keep the tranny fluid 30*+ cooler going through the rad cooler. I'll also sh!tcan the original trans cooler and install a heavy duty aftermarket cooler (j cAT you were right!!! ). I also have a programmer so the 160 would be beneficial for increasing timing.

2000CAYukon

In my experience, the 160 can be an issue in the winter. It is like turning down the temp on your water heater. You will find that you need to run the heater on higher temps to get the same level of comfort in the cabin. You can always run 160 in the summer and 180 or 195 in the winter (like the old days).

//2000CAYukon

jtmarten

Finally had a reason to drive the beast after installing the 180* superstat. Temp now reads just over the first large hash mark (about 1/4) instead of at or just under the 210* mark. Hopefully no trans issues from now on.

MagicRat

I humbly suggest that unless you are towing ALL the time, consider putting the higher temp stat back in.
Your ECM is likely designed to work with the 195 stat in order to produce the lowest emissions and get the best fuel economy.
It may interpret the lower coolant temp produced by the 180 degree temp as being too cool and may be richening the fuel mixture slightly trying to warm it up.
Therefore, the 180 stat may increase fuel consumption slightly, not only due to the richer mixture but also because a slightly warmer engine is more thermodynamically efficient.

Also, one of my auto service textbooks demonstrates that a 195 stat reduces engine wear over a 180 stat, because (up to a point) a warmer engine and engine oil experiences less wear.

Imo unless the engine actually boils over, a lower T-stat is not the best way to correct for an overheating trans. Get the biggest trans cooler that you can find. Also consider installing an electric transmission temp gauge. The sensor part screws into the trans in place of one of the fluid pressure test ports in the side of the trans.

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jtmarten

Actually I saw just the opposite for the fuel economy. I was getting 13.3mpg highway prior to the t-stat, and only got 11.7 on my trip to Detroit. I normally track mileage so I'll be watching it closely with the cooler t-stat. The cooler t-stat will also benefit ECU programming changes.
It has the factory trans cooler, which is fairly large, but I'm not sure how efficient it is compared to some of the aftermarket coolers I've looked at lately. I'm not sure if I should replace the factory cooler, or install an additional cooler after the factory cooler. Some I've seen have fans so they could be mounted just about anywhere and still cool. I've been looking at trans temp gauges too and will be installing one.
I was kind of suprised the tranny got a little too hot since the boat weighs about 6800lbs, and the Sub is rated for 10Klbs.

j cAT

If your vehicle could not keep the temp at 195deg f when towing you need a transmission cooler larger than what you now have...also you never tow in 4th gear...this can damage the transmission by over heating..

the proper temp is required for proper engine management of engine controls....if this were 1965 I would not say this...

jtmarten

The temp held great, never went up beyond the point the gauge showed without towing.
I've been following the guidelines in the manual for towing. Use OD unless it has to downshift/upshift frequently. It pulled the load with no issues, couldn't even tell the boat was back there most of the time. If I still had my K1500/4L60E I'd leave it in 3rd for towing.
The trans had to be just a deg or two over because a 10min fuel stop cooled it down enough to run normally again. It was not hot enough to show any bubbles on the dipstick.
I'll be towing it tomorrow about 85mi to the lake so I'll see how it does.

j cAT

when a vehicle engine overheats the transmission fluid needs changing especially when it occured in a towing situation...

towing or hauling heavy loads in OD is damaging to the transmission...this is common knowledge.....

jtmarten

Overheats??

j cAT

with towing this load your surprised the tranny got hot....your kidding I hope...

remember boat 6800lbs plus you and other items carried is what is closing in on the max load ....then the mountain climbing....
its know wonder the tranny shifting was altered.......

jtmarten

Not suprised it got hot, just suprised it got just hot enough to lose OD. No mountain climbing here. This was on flat land from Detroit through Illinios.
Roughly 65mph, 2600-or-so rpm, and cooler weather, some rain to help cool things down.
Even when getting to Colorado and some hilly country, no issues while maintaining 55mph.
It'll be around 80* this weekend when I tow it to the lake. I may install a temp gauge this week to monitor.
I may just add an additional cooler w/fan to be on the safe side. Cheaper than a new tranny!
When I go to Blue Mesa reservoir in Gunnison for the July 4th weekend, she'll be in 3rd, maybe 2nd, while trucking through the mountain passes.

Why the general assumption that Colorado automatically means mountain driving? I take cycle cruises and carve up some of the canyon roads every summer, but that may be the only mountain driving I do all year. I think I've towed a boat to a mountain lake once in 9 years of boating. Water is just too dang cold! We have rolling hills, but lots and lots of flatland. My house is at 7300ft, the lake in Pueblo is around 4600. But that elevation change is made over an 85mi trip.

j cAT

I've never been to colorado but I have seen many pictures of the state with white mountain peaks every where...

even in massachusetts we have hills that are steep that put extra work on the drive train...the highest peak in my area is 1000ft....but most of the land has rolling hills of 100ft at most..no long grades changing thousands of feet...in elevation...

you do need a larger cooler with your boat towing load ,, plus equiptment, regardless of any grade climbing....your near the max..

changing of the drivetrain fluids would be a good way to ensure a trouble free season...

jtmarten

Absolutely a total fluid change will have to be done before I start towing every weekend. Fluid is still a nice light red color.

Would you suggest replacing the factory cooler with a more efficient one, or add an additional cooler?

j cAT

I would measure your cooler then look at the aftermarket coolers available...then decide if your cooler should be replaced..

I used a 10,ooo lb rated cooler and found the engine/tranny ran very cool on the hottest days a/c on and towing..

when mounting remember to keep a 1/4-1/2 inch space between the cooler and the a/c condenser...

since I last responded it came to me that your running hot may be due to insuffecient coolant pressures...If your system does not run at 15psi the coolant at high elevations will cause the coolant to boil at much lower than 212deg F....

check coolant system [pressure test] then replace the coolant pressure cap....see if that is the problem...

Elbert

1 180 degree thermostat from a 95 Z28 will work, have the same in a 1999 5.7 Yukon engine, I assume you are talking about a 5.7 gas engine?. Don't know how heavy the boat is or how low geared you truck is....it may not to be the best thing to run in OD.

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Elbert Clarke