HarryK

Well, changed out the replacement last night. Took the first Katech 174 out and it was marked at 79 degrees C. New one arrived was identically marked. Installed new one and did static test in driveway last evening..ambient about 80 degrees in shade. Put the OBDLink MX on the plug and monitored the temperatures. Also put my hand on top radiator hose and waited for hot water to flow. At about 168F, hot water began to flow through the top radiator hose and continued to increase in temperature. Cleaned up and put everything away for the next day. Next morning, ambient 73F, cold start and also opening at 168 degrees F. Easily 10 or 12 degrees hotter than the previous Katech 174. This was about 10 minutes into the start cycle (AC off no fans). Two minutes later it was down to 160F, two minutes after that it was at 168F, two minutes later at 172F. A lengthy road test (about 10 or 15 miles) through light city traffic and also 45 to 55 mph zones , keeping AC off, revealed ECT going from about 165 to 180 degrees but mostly between 170 and 178 for the majority of the time. Line at Drive-thru showed temps increasing to 200+ with fans coming on to bring temp down to high 170s. Again, efficiency of this radiator with the V6 with air flow is impressive. I sent the previous one back. I think I'm done changing thermostats (but then I remember I still have to do the 6L80 one with my Surecool kit). Dan from Katech said they would refund my first purchase and test the return out. Hope it works out. I'll just call it the correct $150 thermostat installed with free labor...(shipping twice here and once back)....LOL Oh well...Happy engine....

Yes, absolutely. (Really like your setup). Remember though, if it is a 174F then then it should open right around there,maybe fully open a little higher (Katech lists +7 degrees as a tolerance so I don't know if it means it starts to open at 167 and fully open at 174). When I first changed to the factory OEM 207, the top radiator hose would get hot right there at 205/206 or so....the stat in question on the truck now starts to open at 156/158F. I would keep the one I have (which I really think is the 160) but I bought the 174 so the ECM wouldn't trip the P0128 and put my fans on full. I believe it will do this after too many <168 degree drive cycles. With a 160 thermostat, and no change to the electric fan schedule, the coolant may reach over 200F while stationary, occasionally taking care of this problem. However, in the winter when you're idling and the coolant doesn't reach past 168 for a few cycles the computer thinks your stat is stuck open. With a 174 it should be fine. We'll see what the changeover brings...

Interim update: I did two more tests. One was in the driveway cold start while monitoring temp with the OBDLink MX and keeping my hand on the upper radiator hose. At about 156 to 158 degrees, the hot water started flowing in... Second was at 50 to 55 mph for 5 to 6 miles after warmup. Temps fluctuated but always trying to get back to about 165 +/- I called Katech and talked with Dan who was very helpful. He said that sometimes in applications the cooling system is so large and efficient that it overwhelms a thermostat but mine is stock Silverado 4.3L. But it is possible I received the incorrect one. I ordered a new one and will send the old one back in when I do the job upon new arrival. Katech was very accommodating but I had to order a new one ($91), then they will credit me when I send the old back in. This way truck is not down for 2 weeks. Shipping is very high ($18) for small item even though well packed, still small box. Even express mail would be less and it is sent regular UPS. Oh well...will let you know...thanks for commenting/helping out.... By the way, it's still great to open the hod and feel the immense difference in heat when the engine is running 40 degrees cooler. As pokismoki said, there's no way that 210 degree coolant system is good long term for all the parts under there, no matter how engineered they are Thanks!

Pokismoki, yes you're correct, if the transmission thermostat remains, the fluid goes out to the radiator cooler at 192F and even if it is cooled and returned, the transmission stat will keep it at 192. But it's better than the transmission sending it out at 192 into a 207 degree coolant enviornment and actually raising the temp for the fluid's return to the transmission. At least I think with the coolant about 175 (and lower on that side of the radiator, it won't raise the transmission temp as the factory set up would. Hope to know more about my Katech this week.

That's a comprehensive chart GB. Remember, the temps I'm typing up here are for the engine coolant I'll deal with the transmission bypass shortly by installing the Sure Cool kit when this is figured out. As for the transmission thermostat, yes the pill contents are interchangeable with the new 158 degree replacement from GM bu the actual thermostat is not. The housings for the 2014 and I believe some 2015s have different fittings for the transmission lines (C clip vs. a bolt pressing in a bracket.). So you can't just swap out your thermostat for the new one unless you buy the new lines if you have these early build Silverados. You are correct though that you can take them apart and replace the new guts into your original housing. As I have the Sure Cool kit waiting, I won't have to buy a new trans thermostat to do that (Each lowers the temp in it's own way, with GM I believe using an actual element inside and the Sure Cool kit using a pressure system which I believe equated to about 160 degrees with a fail safe. So much stuff to know for this thing. Hope to verify my coolant thermostat this week and then attempt the Transmission one. GB thanks for the chart..impressive work.

I'm currently in south FL and the heat becomes oppressive here. We have a couple of cool days now before the run up to the summer. I did read that the transmission stat opens at 192F. But before, with the stock 207F coolant thermostat, that 192 would get pumped into the 207F coolant. (Although I have the V6 4.3L so the transmission cooler lines go to the passenger side radiator tank (cold side) so the coolant temp may be a bit lower there where the trans cooling lines are inside.). Anyway, the Sure Cool delete kit for the trans stat arrived a couple of weeks ago. As I mentioned though, one thing at a time and I wanted to do the Katech 174 first. As for the updated TSB on the trans stat, I believe GM changed the fittings in 2015 or 2016 that go to the transmission thermostat. My 2014 has C clips going into it and the updated GM thermostat (which is rated at 158F) will not swap in. I would have to buy the entire line set with it. I hope to get the truck out this week for the testing that GB recommended. I did check the packaging today and it was marked as the 174F coolant thermostat. Thanks for the info...If you have thoughts on the ECT sensor right next to the coolant thermostat housing let me know. I was going to change it out.

Interesting, thanks GB, I'll let you know as I run some road tests. I believe the P0128 trips after a certain amount of drive cycles not reaching 168 degrees (from what I've read). Makes sense now for my last couple of years ,most likely had thermostat failing slowly...(had truck for 4 years..bought it with 178,000 miles...dash temp was always around 11 o'clock/11:30 lately). With the new OEM stat installed, It seems to hang steady at the 210 degree 12:00 o'clock position. Again, from everyone's input and my observations with the OBDLink, , it seems to be programmed to hang there for a 30 or 40 degree range, presumably to not panic people about normal fluctuations. I will say though that I love the coolness of the engine compartment compared to before...feels good to not subject everything under there to such high heat. An added benefit would be that the trans fluid gets cooled down now when it goes through the radiator instead of heated (it's already at 192 when the trans stat opens (I know,,waiting to install sure cool bypass...one thing at a time). On to my testing...

Thanks..no offroading...just reliability as second vehicle at this stage in my life (close to social security age)...wondering on what you think about the Katech and how to see if I received the correct one..

Hi all, I read through all of the coolant/6L80 discussions I think...quite a bit of research and some very knowledgeable people spent a lot of time on it. My high mileage 2014 4.3L 1500 4WD didn't light the MIL but the fans stayed on full even after engine shutdown. Dash coolant temp gauge was pinned left at 160. Got new thermostat from GM, installed it and reset P0128. What a difference in the heat the engine was giving out (When ambient air was about 88 degrees and high humidity. Never felt anything like that before. Put OBDLink on it and it was pretty steady holding the ECT at 208...dash gauge was at 12 o'clock...Found out new OEM stat is 207 degree. Ordered a Katech 174 and installed it. Some findings: (all temp readings by OBDLink plug in.) At idle in the driveway, while checking for leaks, the temp goes to 212 (takes a while) at which point the fans turn on and it cools it down to 185 +/-. Fans appear to shut off about 210 or so.. Few days later, ambient is 62 degrees, test drive brings the temp down to 158 and steady there. Side roads about 5 or 6 miles. 30 to 40 MPH. Sometimes goes to high 170s. At idle in store parking lot, temp rises very slowly to 200 or so and more. Didn't wait for 212 this time but turned on A/C to bring fans online and temp began to lower almost right away..goes down to 170s or so while parked..this tells me that the radiator is extremely efficient with air flow going through it. Now wondering if the ECT sensor next to the thermostat is a factor in this and needs to be changed because it became 'lazy' or is just malfunctioning. Shouldn't temperature be holding about 178 +/-? Will take some more readings but I'm wondering if they sent me the 160 one instead..I thought it was stamped with '79' but not sure...... ......just starting the post with some basic info here...appreciate any thoughts or recommendations..Thanks! Note: Going by remote OBDLInk MX and referencing the dash temp coolant gauge, the first small mark on the left past the 160 correlates to 125 degrees, the next one correlates to 150 degrees, the next one to 168 degrees and when it reaches 12 o'clock (dash 210) the OBDLInk reads 185.