The engine in my signature rig never gets above about 165 F. I replaced the T-stat with an OEM Ford part with no change. I've verified my guage's accuracy using an infrared thermometer. I understand it's not good for the engine to run so cool, but I have no ideas how to proceed. A search yielded no help.

 

 

I have had the same results by aiming an infrared gun at the thermostat housing.

We don't really concern ourselves with coolant temperature - we are more concerned with Engine Oil Temperature. So much so that there is no coolant temp sensor feeding the PCM on automatic trucks - but every rig has an oil temp sensor feeding the PCM.

 

I installed the OEM 193 F. t-stat.

As for the Oil temp, if it feeds the PCM, I should be able to bring it up on my Scan Guage.

Thanks to both of you for the replies. I'll follow up after I check on the oil temp!

 

I'm disappointed to learn my Scan Guage, apparently, doesn't read oil temp. Any other advice y'all?

 

I don't understand why anyone wouldn't be concerned with the low coolant temp, I would be.

Has it always run cold or something that suddenly started?

 

Since these rigs don't have a coolant sensor attached to the PCM, there are all kinds of methods to get the coolant temperature that end up being inaccurate - so I don't scream for the hills at the first sight of a thread with high or low readings. That engine oil temperature is the gold standard because of the dubious nature of coolant temp.

No engine oil temp on your scan gauge? Let us know make and model (or app), and one of us may have the setting that works.

 

Whether the PCM sees temp or not, the gauge and infrared thermometer both indicate it's running cold. What am I missing here?

What I've read is that the coolant and oil temps should be pretty close to each other if everything's right, but they can be very different if there's a problem so knowing one is up to temp while ignoring the other doesn't seem to make sense.

 

The thermostat holds the coolant back until the right temperature is reached - and idling doesn't always allow the engine to reach full temp. Put that bad boy in second gear and run it up to 2800 RPM while driving down the road, and you will see that temp reach what it's capable of. It won't blow up the truck - I've done it many times to cycle the thermostat when flushing the cooling system. People who tow heavy also reach those RPMs in a lower gear to climb hills for extended periods of time. One of the tests in the Ford manual is to run the engine up to full throttle in neutral for 2 minutes... so Ford feels you can't hurt it at high RPMs either.

Aiming the gun at the top of thermostat housing is aiming at the cold side of the thermostat... aiming at the water pump yields the temp on the hot side - assuming it's not insulated with grease. If the water pump is not circulating the water, or if the coolant is super low - you can get an artificially low reading on the coolant temp. I've pulled one of these engines apart, and I've filled the coolant system more than once. The pump blades are metal, and the cooling system holds 8 GALLONS. If you are that low on coolant, or the pump isn't turning, and you don't notice either... we need to talk.

 

Tugly,
Right now I'm tied up working on a slide out on my 5th wheel. I will get back to you on the model of my scan guage, etc soon as I can. I appreciate everybody's help here, thank y'all.

 

OK, I'm back. I was wrong about my Scan Guage. It CAN be programmed to read additional data through it's XGuage feature. Engine oil temp is one of those that can be programmed in. You can find the numbers needed to add to your list of readings at their website. Soon as I get the time, I'll be doing that and will let y'all know.
BTW, I'm afraid I can't say for sure if this is a new problem or not. It's been a long time since I last used the truck regularly, and my old fart memory just doesn't want to cooperate. I wish I knew too!

 

OK, I got my ScanGuage set up and took the truck for a spin today. Not towing, but drove about 7 miles in 2nd gear in 90F ambient. While my water temp guage read the same, about 165 F, the oil temp was running right at 200F. I then took my IR meter to the t-state housing. I was getting really inconsistent readings, some parts showed right at 180F, or so, others as low as 165. Multiple readings of the same spot were inconsistent The highest reading I got with the IR was at the aftermarket coolant filter outer case, right around 190. I trust this reading the most because it's reading through relatively thin metal, and it's fed straight from the top of the block, right next to the thermostat. Perhaps the readings around the t-stat fluctuated more than at the filter was due to the effect of the fan????

So all that said, It looks to me like my analog guage or sending unit have started lying! Anybody have the knowhow of troubleshooting this? The guages are Auto Guage, Pro Comp(?) Ultra Lite(?) I have trans oil temp, exhaust temp, and water.

Anyway, it just occurred to me I can check the accuracy of my tranny oil guage using the XGuage feature.

Any comments appreciated

 

That's excellent news that your engine isn't running cold - all those temps sound normal for a warm day. I knew that ScanGauge would work because so many people use those, but I couldn't guide you through it since I use Torque Pro and other apps.

 

Rich is right about the unreliable results of external measurements, even when using high quality IR guns. For the IR to accurately read the temperature, the metal surface needs to be scrubbed clean and painted black for optimum heat transfer through the metal to the IR sensor. Dirt or grease will screw up the reading because they change the efficiency of the heat transfer. Heck, even a fresh coat of high quality white paint will give you false readings just because white does not transmit heat as well as black.

 

Be aware that your scan gauge is also going to read a higher transmission temp because it uses the internal temperature sensor that the PCM uses and most gauges use a sender placed at a test port. The temp reading in the test port is usually 10-15 degrees cooler, so don't freak out.