Changing to a 194⁰ Aftermarket Coolant Thermostat

mikeyk101 · February 6, 2023

I recently changed out my coolant thermostat on my 2016 5.4L 6 speed after experiencing problems that suggested my stock thermostat was sticking open. I verified with an OBDII reader that I was having undercooling problems. I saw a recommendation by @16LT4 that he used the Motorad 194⁰ instead of the stock 207⁰ thermostat. I did a bunch of searching and saw that I wouldn't have to change any tuning like I might have if I went to a much lower temp thermostat. I also liked the idea that coolant would start fully circulating at a slightly lower temperature. I figured I would give it a try. The install couldn't have been any easier. Swapped it out in no time and the dash temp gauge went up to 210⁰ mark and stayed solid. I didn't verify with the OBDII the actual temperature but I know that although not completely accurate, it would show larger changes and it wasn't moving so it worked.

When I was searching, I kept looking for more information about thermostats and cooling especially when towing as that is important to me. I wasn't finding much. I am assuming that getting the coolant fully flowing slightly earlier could only be a benefit. Most of the time when towing my 25' toy hauler (6200lbs loaded) I had no cooling issues and travel mostly flat or slightly hilly areas. But when climbing some extreme grades last year, I did see the coolant temp, oil temp, and trans temp rising significantly. I'm aware that trying to race up grades is a bad idea and also use tow/haul mode as well as proper gearing. I did change the trans thermostat to the updated 170⁰ one after this. (Ooops, I meant the updated 158⁰ one...) Now I have the 194⁰ coolant thermostat installed.

I'm hoping that the updated trans thermostat change out as well as the newly installed coolant thermostat can only help with providing more efficient overall operating cooling when towing? And by changing from a 207⁰ to a 194⁰ coolant thermostat, is there any other benefits that I may see?

Edited February 6, 2023 by mikeyk101

16LT4 · February 6, 2023

I monitored ECT with scan tool after making the change, and it stayed right at 195-197*F. The T-stat opened up as it is supposed to, and the fan was on. I went with the lower T-stat not because I care much about ECT, but rather its affects on plastic components, and the ability of heat to plasticize rubber seals. My BMW has ran at 220-230*F for the last 200k miles without issue, other than heat-hardened gaskets.

Within 10 miles of driving, I did notice the on-board display of average fuel mileage increase by nearly 20%, and that's with nearly 100 miles on the current trip odometer. The truck has a smoother idle too, now that it isn't running fat. Fuel trims had indicated over-fueling, so after a few more miles I'll pull that data.

Edited February 7, 2023 by 16LT4

mikeyk101 · May 28, 2023

I had a weird thing happen today. I was getting ready to head out this morning and temps were right around 60. I did remote start for my son who was getting in while I was still finishing getting ready. It probably only idled about 2 minutes before I jumped in to head out. About a mile down the road, I happened to glance at my dash gauges and saw that coolant temp had risen to the first hash mark above 210. Very unusual. Since I changed the thermostat, it will normally rise to the 210⁰ mark and hold steady. It did finally drop back down to the 210⁰ after several more miles. About 10 more miles down road, I made a quick stop to grab some breakfast for us and head back out. I ended up plugging in my OBDII device and monitoring the true coolant temperature. During the drive, I never saw the gauge move up again but the actual temps were running between 205 and 215. When accelerating, it would jump a bit but then drop back while running a steady speed. We got to where we were going and truck sat parked for about 2 hours and while heading home, gauge stayed steady at 210⁰ and actual temps also stayed pretty much between 205 and 210⁰.

So what would have caused the coolant temp to spike like that? I don't know what the actual temp was when that happened but I know that it had to have gone a little north of 220⁰. I wasn't running hard and the truck had sat all night. I think I'm going to have to monitor this much closer now for a bit. I put a OBD splitter harness so I can keep running my Range AFM delete and my BAFX OBDII reader.