If I want to instal a second coolant temp gauge, if I put the sensor in the upper radiator hose should it ready almost the same temp as the factory sensor in the head?
By cutting the hose in half and putting a āTā fitting in it.
I donāt know, I have not purchased one yet. I was just thinking that last summer when using a laser thermometer I dont think I ever got temp readings of the head anywhere close to 222 even when thatās what the gauge read. Iām just wondering if there could be an issue with the new sending unit or gauge. If the scan tool reads 222 degrees but my laser thermometer at the head reads 200, is something wrong?
What would be a better option, to put an adapter in the upper radiator hose, to use a ātā fitting and use the same plug hole for the factory sending unit and the new sensor, or drill and tap a new hole?
While the truck was idling yesterday in 68 degree weather at the dealership with the AC on, the scan tool read 197 degrees.
I dont have a scan tool, but today while idling in the same 68 degree weather with the AC, my laser thermometer consistently took these readings:
Upper radiator hose- 165
Lower radiator hose- 135
Intake tube directly at the coolant temp sensors - 175-179
So, either my laser thermometer is wrong, both coolant temp sensors are wrong or there is a huge difference between the temp of the coolant and the temp of the outside of the tube at the same location. Is it possible that even with new sending units, both are reading too hot? What could cause this other than trapped air at the sensorsā ports?
I purchased this gauge and ordered the adapter on eBay to plug the sensor into the upper radiator hose. This sensor will only be about 5" down the line from the factory sensors which are located very close to where the upper hose clamps to the radiator. I should have everything hooked up by next weekend, then memorial day week I will be taking a 6 hour round trip in the truck to pick up some weightlifting equipment, so it will be a good test.
That looks like a nice little setup
In the event that overheating is continuing you still might consider:
Vacuum test for a partially clogged exhaust.
At near 200k miles maybe the engine is getting a bit weak and struggling a bit with a load.
Any chance that brushguard on the front is blocking or disrupting airflow? Sometimes the small things can create an aggravating major problem.
Some years ago one of my sons hit an animal on the highway and knocked the small airdam off of his Camaro. With highway use, the engine temps would run 30-40 degrees hotter because of this missing piece of plastic.
My other son has a 96 Camaro RS with an F1 bodykit and some years ago he bought a specific for the car bra. After the bra was put on, the car would overheat on the highway although not enough to worry a lot about.
After looking at it, I found that a couple of small ports in the front airdam were partially blocked by the bra. Removed the bra; no more overheating.
The bra manufacturer swears the blockage is not a problemā¦ 
I finally got my mechanical gauge installed. It was a chore getting the 3/4" fitting through the firewall, but I finally got it.
It was 83 today and on the hwy at 65 mph with the AC on it hit 196 degrees. Thatās warmer than I expected. Iām going to load down the truck on a warm day this week and see how it runs.
Gauge
Well after driving he truck on the first warm day I have nothing but bad news. The mechanical gauge works great though. At 65 mph, 2600 rpm and 90 degree air tempā¦
The average for the trip was 210 and the factory gauge looked like thisā¦
Going up slight inclines without even changing the rpm averaged 215
With no AC on the truck averaged 200
The factory needle starts its upward climb at exactly 204
Here is the 215 pic
My vote is still for the use of a vacuum gauge to determine if thereās an exhaust restriction or a high miles engine that is just getting tired.
How sure are you that all of that hardware on the front (brush guard, winch, lights, etc) is not disrupting airflow through the radiator?
That looks like a ton of airflow restriction to me.
Iām sure it restricts it SOME, but itās not the cause of this issue since it has all been on the truck for 7 years and this issue started last summer.
Iāll see if I can rent a vacuum gauge.
They are pretty cheap. You just need the different tips to hook it in to the system. Sorry, I have kinda lost track, did you check timing and compression?
I checked timing but have not done the compression check yet.
I couldnāt see the radiator but if it is original it may have to go. Most radiator shops would have told you to get a new one if there were fins missing. Look on the back side of it and you will see if any are gone.
Your temps are high but not crazy high, so even if the radiator looks fairly good you should consider getting a new one. Look carefully, if most of the fins arenāt smooth or if they are generally in ratty shape like parts of them missing, you need a new one. If running the heater full hot and full speed cools things down, replace the radiator. It should cool things down even with a good radiator but if more cooling is good, maybe ditch the radiator.
Looking at the picture of the truck, there isnāt enough air getting to the radiator. That shouldnāt affect the performance at idle, and a missing air dam under the radiator should only affect a truck in motion. So I think a new radiator will still help.