Greetings All,

With a recent spate of 100+F weather, my '02 V6 has been running a bit on the hot side. The temp never climbed very high, but when worked hard, it would briefly hit about 5/8 or 3/4 at the most. Obviously something isn't right.

My first thought was the thermostat wasn't working properly. I changed that last night but no help. With my trusty infrared thermometer, I verified the top horizontal hose (across the front of the engine) was right on the money in the 195-200F range, which seemed perfect for the new 192F thermostat.

However, my scanner shows "coolant temperature" at approximately 225-230F. From what I understand, the early V6 engines use a Cylinder Head Temperature (CHT) sensor instead of a coolant sensor like on most vehicles. I figure my cheap scanner has labeled the CHT value as coolant temperature, as there is no sensor directly reading the coolant. Per my Jaguar training manual, the CHT directly measures the metal temperature, not the coolant, to allow operation of the failsafe cooling strategy even if coolant has been lost.

Does that 30F split seem excessive? It would appear the CHT sensor has started to fail and is indicting higher than it really is. Or do you think the metal of the cylinder head, as read by the CHT sensor, is really that much warmer than the coolant?

FWIW, before anybody asks, the radiator return hose is showing approximately 140F, indicating a healthy 60F drop across the radiator. Also, as best I can determine by temperature, the radiator bypass passage (used for engine warm up) is being properly closed by the thermostat. I'm pretty sure I'm looking at an indication problem, with a false high reading.

I'd be curious what anybody else with an early V6 has for "coolant temperature" (or CHT) on their scanner once warmed up. Also, please check if the hose across the front of the engine reads in the 195-200F range, so I can see if it's normal to have much of a difference between actual coolant temperature and the CHT reading.

Thanks for any help.

 

It was my expectation (but I don't know for sure) that the PCM would convert CHT's reading into an ECT with a different (lower) reading.

It will be ECT that your tool sees, be it a faked value or otherwise.

So, my feeling is it's too high.

Any other 1999-2002 V6 owners who can read their ECT please (any cheap OBD tool should work)?

 

Your figures seem normal to me. But at that CHT the needle should not be more than a few millimeters away from the middle. 5/8 or 3/4 would mean much higher temperatures.

 

For ECT (or similar name as ordinary OBD tools can read)?

You're not using a tool that knows how to request CHT? (Such as WDS or IDS.)

 

Yeah, but I also wonder if the CHT value is deliberately skewed to approximate coolant temperature.

More details about the deliberately misleading gauge here:

https://www.jaguarforums.com/forum/x...e-gauge-62813/


That's a different model, but the behavior is the same on my '02. When my scanner shows "coolant temperature" above 230F, the needle starts to climb from the center position.

Since I'm reading 230F under normal conditions, there is absolutely no reserve. It doesn't take much, such as hot weather or working the engine a little, for the needle to climb.

That's why I've asked what others are seeing as normal "coolant temperature" on their scanner. I'm pretty sure I'm dealing with just an indication problem. Guess I'll know after the CHT sensor arrives tomorrow.

 

Let's hope someone with a 1999-2002 3.0 car will post an ordinary OBD tool's readings for ECT (engine coolant temp).

(They won't be able to post CHT as that is not an OBD sensor. As I posted, I reckon CHT is scaled to become ECT so the OBD tool is happy and so the car meets the required OBD laws.)

If your tool shows anything like 230F then I'd expect the PCM would have the fan(s) on full and might well leave it/them on after the ignition is switched off.

 

You could try a good-used CHT sensor and substitute to verify that yours is not faulty?

bob

 

Nope, just an iPhone app and a Bluetooth module plugged into the OBD II port.

 

Yep, it had been doing that, but only on the hottest days. Must have been teetering right on the limit. Didn't seem out of the ordinary to me, so I was never alarmed about that.

 

The highest I have ever read was around 225 F. That is at 100 F ambient temp either in rush hour traffic or motorway uphill in the Alps. This is CHT, and the needle is slightly above middle.

I do not think there is any recalculation from CHT to the actual coolant temperature.

 

How do you know it was CHT? Were you using a special tool?

An ordinary one should not know how to report CHT and instead report ECT. (Which is internally created from CHT it seems.)

225F in rush hour may be right but seems high.

(The good news is that it's below what kr98664 has seen.)

 

Much happiness to report. A new CHT sensor arrived yesterday. I made some comparisons with the old one. Here's my test set-up on the stove, with both sensors and a thermometer:




Much to my delight, I found the old one reading about 10% higher than the new one at any given temperature. For example, at 190F, the old sensor indicated what the new one did at 210F. Phew, what a relief. If the old sensor wasn't bad, I'm not sure what I'd have done next. There's no guarantee the new one is correct, but the results seem about right.

I swapped in the new sensor, a piece of cake. For reasons unknown, Jaguar engineers located this sensor in a very accessible location, between the coils for cylinders 4 and 6, on the US driver's side. I hope nobody lost their job over this serious breach of accessibility protocol.

On a test drive under nearly identical conditions, my cheap scanner showed "coolant temperature" around 210F, where it had been 230F. The dash gauge needle stayed glued half a hair to the left of the center mark, where it had always lived until recently.

The best part of the whole experience was parking my old pickup at the Jaguar dealer after work. I had just changed an A330 main tire, a very messy job, and was still wearing the evidence on my decidedly blue collar uniform. This was literally the first time I'd entered any dealership without being accosted by a pack of eager salesmen.

 

Hmm, the saga continues, sort of. After more driving, I had noticed the scanner showed up to 225F on several occasions. I got to wondering about the new sensor. I had a spare sensor because after ordering one online, I was able to get one quicker through the dealer and I needed the car.

So I swapped out the new sensor from the dealer with my second new OEM sensor. Much to my dismay, this one read about 7 or 8 degrees higher under similar conditions. The variance was just enough to occasionally go above 230F, the point at which the needle climbs above center. I then swapped back for the first OEM sensor, the lowest reading one of the three. With this one, 225F is about the max I see, but that still isn't much margin below the 230F trigger point.

Just for giggles, I shot my infrared thermometer on the horizontal coolant tube at the front of the engine, just below the throttle body. With a new 192F thermostat installed last week, I'm seeing right about 195-200F, which seems perfect. Can I get somebody else with an early V6 to take a similar reading after a normal drive? I want to be positive I don't have an actual overheat condition. Comparisons with similar models would be a huge help.

In this picture, I'm pointing to the location:




Thanks so much for any help.

 

With age these sensors tend to show higher temperatures than actual so your findings that the oldest one shows the lowest is somewhat unexpected. Why dont you test the sensors in boiling water. That is the only simple way to make sure. Or you could check the voltage but that requires knowing the temperature as well (0.6 volts at 194 F).

 

Bump.

Anybody with an early V6 have an infrared thermometer? Still scratching my head if I've got an indication issue or if the engine is really running warm. Can anybody throw me a bone?

 

An update:

Turns out I had two faults, followed by two new parts bad from stock. For anybody who ever says "Such and such can't be bad because I just replaced it", you should read on.

The first fault was the existing MotorCraft 192F thermostat. After I replaced it (Motorad brand 192F), I had some improvement, but the temp was still showing higher than I'd like to see. After messing with the indication system (the second fault, more later) and still not seeing enough improvement, I tried a third thermostat (Carquest 180F). I decided to go with the 180F to make sure I fixed the problem.

I had enough time to compare all three thermostats. I suspended them side by side in a pot of water on the stove. The original barely opened at 192F. It was clearly bad. Much to my surprise, the first replacement was also bad. It never opened more than halfway, even when I heated the water all the way to 212F. The second replacement was fully open at 180F as designed, so that's the one I installed.

The second fault was with the indication system. The original CHT sensor was reading about 10% higher than the first OEM replacement I tried. I don't have any means to verify calibration. All I could do was compare resistance at a given temperature, using the pot of water on the stove. At 180F, for example, the original gave the same resistance reading that the replacement showed at 200F. Which was wrong? I tried a second new OEM sensor, but it landed between the other two. So I had two new OEM sensors off by 5%. That may not seem like much at first glance, but that's 10 degrees at 200F.

I currently am running the tested-good 180F thermostat and the hoped-good sensor that reads the lowest of the three. All has been good for the past week like this, so hopefully this issue is resolved. But next time somebody swears a part is good because it's brand new, forgive me if I break out laughing.

Also, I think the thermometer reading I requested at the crosspipe isn't of much use. Even comparing the good 180F thermostat with the stuck 192F one, the thermometer reading was about the same. My current hunch is there is too much heat blowing back from the radiator, making it impossible to accurately determine the coolant temperature inside that pipe.

 

180 degrees is well below what your engine is designed to run at.

 

It is, but it's probably (or is it?) better than being too hot.

I understand running cooler will reduce fuel efficiency and increase emissions, but too hot would put the engine at risk of serious damage.

Anyone know more and what the hottest safe sustained temp is?

 

The problem is that the actual running temp is not precisely known. The 255 observed with the new sensor is known to be within limits.

 

Something to keep in mind: 180 degrees is not even 7% cooler than the original 192 spec. In my situation, is this workaround perfect? Not really. Adequate? Yep, so I'm okay with that.

In a perfect world, I could have got another 192 thermostat and tested it before installation. However, I was getting tired of working on the car and so settled for adequate. Maybe the engine is getting a bit tired (275k miles) and so tends to run a bit on the warmer side. Who knows?

It is interesting to watch the temperature display on the scanner. The temp slowly fluctuates within about 15 degrees, based on engine load. Remember, this is the actual cylinder head temperature, not the coolant. The peak I'm seeing now is about 220F, which seems to be a reasonable margin below 230F when the dash needle starts to climb above center.