Hello all!

I just received and installed my UG for my 98 Disco I with 182K on it. I've just installed a 180F tstat and drilled the 1/8" weep hole, located it at 12 o'clock. With my IR temp gauge, I'm seeing 185 - 190F on the outlet of the tstat neck, up to about 195 - 200F at idle.

After plugging the UG in and setting it, I'm seeing about 20F lower on the UG than the hand-held IR temp gun. When the UG says the temp is 165F, the tstat neck is 185F by the IR gun. I've unplugged the coolant temp sensor, and watched the UG show -40F immediately, so it seems the CTS is working properly.

Am I being too much of a worry-wart, or is there something I need to look into a bit closer?

The background reason for the UG and tstat change was the engine became "warm" (just over half way on Disco gauge) when pulling a steep dirt road just outside of Jacob Lake in northern AZ coming back from UT. We were pulling our offroad Adventure trailer (~1,000 lbs) and stopped to let everything cool down. I've adjusted the electric fans to come on at 170F and full on by 180F. I just want to make sure that I'm not overlooking something that will cook the engine!

 

With my 180F stat I'll make 183 at idle on my D1. I could not get the IR thermometer to produce reliable results at various spots, I took this to mean it was being thrown off by air movement. The 165 reading should be the stat warming up when started up. If you are seeing that at other times, the thermostat may have slipped down in the housing, and there is an open arc of space. This allows the stat to behave like no stat installed. Would think just before cold start IR and UG would agree.

Your electric fans are after market? My oem ones come on with the AC and stay on.

 

I have experienced the same results as the op, seems the aluminum is hotter then the coolant inside?

 

That would be true, but 165 on the OBDII port is pretty close to a "no stat installed" situation.

 

Buzz, I agree, that's what has got me confused a bit. After reading your first post, I checked the IR against the UG at start-up, focusing the IR right at the intake where the CTS is located. They were within 5F of each other. Drove into town today, the UG read 165 - 170F most of the way, topping out at 174F w/ A/C on a slow grade. If this is true, great. Even if it IS 20F low, this is still good, as 194F peak is alright with me!

When I got home, I rolled the right front tire up on a ramp and left it running, thinking that I might have a left-over airbubble in the system. Opened up the overflow cap, very little pressure released, squeezed the top hose a few times, only got solid fluid up. No bubbles. Checked the IR against the UG again, and got some very differing reading from the IR, just like you had said. The UG reads a steady 168 - 170F at idle.

It is possible, but unlikely, that the tstat is out of place, as I've had it in/out 3 times. The first time it slipped and was drooling coolant onto the valley cover... learned my lesson there. The second time the temps were in the 200F+ range, so out it came and into the boiling water. Bad tstat! Learned another lesson! The second one was boiled first and read with the IR gun, opens at 178 - 180F multiple times, so in it went. I "stuck" it with a tiny dab of gasket sealant to keep it in place while installing the neck. Using a small flex mirror and a light, I can see it in what seems to be a correct position. No leaks this time. Using the IR gun, it opens at 185 - 190F at idle.

I've replaced the radiator 6 years ago with a new one and installed Flex a Lite 295 dual fans - Flex-a-Lite Fans - Dual 13" Electric Fan Models 295/298 - Truck Customizers. I went with the most airflow I could find that would fit - 4,600 cfm. The fan is wired into the stock A/C fan lead, so operates as the stock A/C fans would. The fan thermometer is set to come on at 170F at 60% airflow and ramp up to 100% flow at 180F. When I put it up on the ramp, the fans were on steady in their "slow" mode.

Can the CTS suffer a "slow death" where it gradually starts reading low as it begins to fail, or does it die a sudden death?

What are your thoughts on this additional info?

 

I would guess that the coolant sensor could become "coral coated" with scale, and you could remove it and sand off any build up. Also not unreasonable for sensor to be bad, or to have a bad connection making sensor read different than it should.

 

Solved some of the mystery of the difference between the Ultra Guage and the IR handheld thermometer.

I read on another thread that the coolant temp sensor will have a resistance of about 300 ohms at 85C, or normal operating temps. After driving into town today, I pulled the connector for the CTS - the ohms were 305 at a temp reading of 175F, which sounded normal. I turned off the engine and checked temps with the IR gun, and found the following range of temps, shown in the photo:



After putting the connector back on, I wiggled the wires, along with the harness that runs just in front to see if there were any loose wires or if the temperature on the UG moved at all. Voila! The temp went from 170F to 100F, then back to 135F - 155F. The idle also increased from 700 - 730 RPM to 1300 then 1500. The pre-trouble code alarmed with P0116 on the UG - coolant temp performance. After returning the harness to its original position, everything went back to normal - idle and temp. The pre-trouble code still alarmed. After shutting off the engine, I looked at the underside of the harness, and it looks like there might be some chafing, which would explain several things!

Here's what I found:



I could alter the idle speed and temp readings on the UG just by rotating this section of the harness. So now I will open it up and check for chafing...

On a positive note, I now trust the UG and CTS more, as it seems to be in line.

 

Also, the cone of detection for the IR thermometer is larger than the laser pointer, and more like a flashlight. Plus air blowing on face of sensor can cause changes.

 

An update on the temperature differentials between the UltraGuage and the IR temp gun. Buzz is correct, the air movement from the fan will distort the temp readings on the IR gun. After I had driven it a couple of days, I burped the radiator again - not too much air, about an inch or so - and re-checked my readings between the two. They were within 3 - 5F of each other. Good enough! I did notice the UG seeming to "stabilize" after the first few days, as the initial readings seemed a bit low.

Meanwhile I was reading some older threads on radiators/temperatures/etc. and saw a post about washing or flushing the space between the radiator and condenser to remove lodged dirt/bugs/debris. I've replaced the radiator about 6 years ago and keep the engine pretty clean, but peeled off the rubber airflow strip at the top of the rad and peaked down. Some accumulation of bugs and a light coating of dirt. I loosened the screws on the top retainers of the rad and tilted it slightly back to allow access for a garden hose and went to work. I saw some slightly dirty water come out, nothing too impressive considering I live in Arizona and do a lot of back-country dirt roads, and haven't flushed it like this since the new rad went in. Allowed everything to drain, re-did the top rad mounts and fired it up. Once the temps came up and the fans came on (electric - Flexalite 295 @ 4,600cfm full on) there was a noticeable increase in the airflow through the rad with the top air strip off. Took the grill off to feel the airflow there, and again a very noticeable increase in airflow. All in all, this took 30 minutes to do, easy and will help keep the old girl alive longer!