Engine hot - A/C off

[onalaska]

Left the house and got this message in the DIC about 5 miles down the road. Checked the gauges and the temp was on the left peg showing no temp at all. The engine fan running at high speed, but the radiator hose had no pressure on it at all and the engine was not hot. Checked the engine temp sending unit connector and it looked OK. Plugged in my scan tool and the engine temp. Was reading normal. Cranked it back up today and immediately had the same message on the DIC. Engine cooling fan on high. After running about 10 min the message went away and noticed the temp gauge was reading normal again. Engine fan turned off and it has been normal since. What happened? Loss of comm? From the ECU? Scan tool was showing normal temp. but the ECU thought it was hot even though the gauge showed it was cold. At least I know I didn't overheat the engine.

 

[ald42]

engine hot??

Left the house and got this message in the DIC about 5 miles down the road. Checked the gauges and the temp was on the left peg showing no temp at all. The engine fan running at high speed, but the radiator hose had no pressure on it at all and the engine was not hot. Checked the engine temp sending unit connector and it looked OK. Plugged in my scan tool and the engine temp. Was reading normal. Cranked it back up today and immediately had the same message on the DIC. Engine cooling fan on high. After running about 10 min the message went away and noticed the temp gauge was reading normal again. Engine fan turned off and it has been normal since. What happened? Loss of comm? From the ECU? Scan tool was showing normal temp. but the ECU thought it was hot even though the gauge showed it was cold. At least I know I didn't overheat the engine.

looks like the electronic gremlins want to let you know there still there!! I get crazy popups every now and then that just go away?? OH you ARE in coldspring.

 

[GizmoQ]

There have been at least a dozen threads over on cadillacforums STS-V forum about this issue. The fix for 90% of the folks was to replace the thermostat.

There's supposed to be a TSB on this.

 

[onalaska]

Thanks for the suggestion Giz. I read that the ECM checks the coolant temp. over time and will set a DTC if the engine does not warm up as quickly as expected suggesting a thermostat that is stuck open. Strange message in the DIC for a thermostat that is stuck open "Engine hot - A/C off". The engine was definitely not hot. I even got the same message on a cold start the next day. Then as strange as it appeared it just went away. I guess it fixed itself.

 

[xlrlist01]

Thanks for the suggestion Giz. I read that the ECM checks the coolant temp. over time and will set a DTC if the engine does not warm up as quickly as expected suggesting a thermostat that is stuck open. Strange message in the DIC for a thermostat that is stuck open "Engine hot - A/C off". The engine was definitely not hot. I even got the same message on a cold start the next day. Then as strange as it appeared it just went away. I guess it fixed itself.

Classic failing thermostat. I don't think it is an easy job (happy to stand corrected) hence schedule when convenient as probably not urgent. Excessive low temperature will block out converter lock-up too.

 

[onalaska]

Thanks for the suggestions. Thermostat makes sense. I changed the coolant in the engine and CAC last month and made sure everything was topped off correctly, but in years past it seems that the thermostat usually goes whenever I have done that on other vehicles as well. Does it make any sense to put a lower temperature thermostat in place of the factory 192 degree one? Does that confuse the computer with the engine running at a lower temperature? and do I have to get retuned to operate better at a lower temperature?

One thing I discovered while changing the coolant in the CAC was that my coolant pump was not running! The connection to the pump motor is loose and moving the wiring around got it running again. That' the first time I have noticed the pump running after shutting off the engine. I wonder how long it has been out! I am probably going to replace it since I don't trust it now. Just bought a Tech2 so I can check things like that since there is no indication that IAT2 temps are higher than normal, but it did feel like the performance was off when it was hot.

 

[xlrlist01]

Does it make any sense to put a lower temperature thermostat in place of the factory 192 degree one? Does that confuse the computer with the engine running at a lower temperature? and do I have to get retuned to operate better at a lower temperature?

For the first question, in a word, no.

Basically Cadillac know how to get the best out of your XLR and running a lower temperature thermostat will not do your XLR any favors. It will hit the economy and will increase wear, as well as causing problems to do with not getting hot enough. There are reasons to drop the thermostat temperature, but those who would benefit know what they are doing and why and thus wouldn't need to ask about it. (They will be involved in extensive track racing, not the odd track day. Even then, it wouldn't be the first modification to make.)

The computer will not be confused as such, although if the temperature is too far out it will result in a fault code or two. If the service engine light is on, it means there is an emissions related defect, which is not a good situation to be in. Why would you want a retune? Cadillac have spent a huge effort getting the correct cooling for your XLR, they really have. The best thing you can do is trust them and keep your XLR fully maintained, including keeping the cooling system performing as intended.

If you are suffering over heating problems, the better solution is to diagnose why and fix it. Lowering the thermostat temperature is not fixing the fault, only the symptoms, if that.

HTHs.

 

[xlrlist01]

Waterless coolant

There is another solution to overheating and that is to use a waterless coolant. I have no connection with Evans and haven't tried this product, though I am considering it for a 1955 machine that has always overheated when caught in traffic.

On the face of it, this shouldn't work, because there is no liquid like water for having a high specific heat capacity (ie its ability to absorb energy) and to retain a very low viscosity (ie be very runny).

However, water boils at 212 degrees unless steps are taken to modify this, using both additives and pressure.

Suppose there was a fluid that didn't boil until it reached a much higher temperature and was nearly as good at holding energy (as heat). If that were the case, it might make a very good coolant. Such a fluid exists, made by Evans, it is available on EBay. The downside is cost. The upside is it gets out of a whole host of the problems associated with using a water based coolant.

You can read up about it here:
http://www.evanscooling.com/ and
http://www.evanscooling.com/products/coolants/automotive/

It is necessary to flush the water based coolant out very thoroughly using their flush fluids, this adds to the cost. Also, it freezes at -40, which could be a problem in some places. I don't know if it expands on freezing.

They quote Jay Leno as endorsing the product, apparently Jay has fitted it to several of the cars in his garage. Watch the video.

 

[MarkSki]

Red Line Water Wetter claims to do the same and you don't have to jump hoops or buy other products to use it. I've tried it in an L98 engine and it didn't lower my coolant temp at all.

A remap of the ECU and a 160*F thermostat DID lower the temp. I was not having a problem, I wanted to run cooler engine temp, introduce a cooler air charge so the ECU would supply more fuel hence more kick in the pants!

You said Cadillac spent a lot of money to make our XLR's run at top form and to maintain the engine as it is, then you type a message about dumping the water out of the system and replace it with an additive.

 

[V Happy]

-Engine-hot-A-C-off

Guys
Talking about the different solutions that claim to lower your temp. I know nothing about them. One thing I do know is your engine was designed to run at the temp of factory stat. I was in the radiator business for 30 years. I read article after article how the wear on an engine was drastically increased with a 160 degree stat. Racers use them a lot because they can get a head start on the overheat and also the denser air. What I am saying is if you are not serious about speed stick with stock.
V Happy

 

[Stella]

When I purchased my car acouple years ago I wanted to change all the fluids in my car so I knew the conditions,etc. After doing a coolant flush I added two bottles of water wetter to the system. My gauge never sees 220. I never had any problems I just used it extensively in my 2stroke racing years and it made huge differences in them. Markski is right cooler operating temps. means denser air charge which the computer compensates fuel delivery. If your driving your car in the winter months yes you wouldn't want to put a lower thermostat in. Your engine would have a tough time getting to optimal temps. Driving your car in the summer months with the lower thermostat won't harm anything. That's exactly why they put intercoolers on superchargers and turbo engines cooler denser air.

 

[xlrlist01]

Red Line Water Wetter claims to do the same and you don't have to jump hoops or buy other products to use it. I've tried it in an L98 engine and it didn't lower my coolant temp at all.

A remap of the ECU and a 160*F thermostat DID lower the temp. I was not having a problem, I wanted to run cooler engine temp, introduce a cooler air charge so the ECU would supply more fuel hence more kick in the pants!

You said Cadillac spent a lot of money to make our XLR's run at top form and to maintain the engine as it is, then you type a message about dumping the water out of the system and replace it with an additive.

Fair point. I could write a long and boring description of automotive design to give more background to this topic and where I am coming from, but unless there is a significant groundswell request, I'll give it a miss. Please note though, that the product I described (which I have not used as yet) is not an additive, it is an entirely different product and one of its key features is that water must not be added to it. Those 'wetter' products work in an entirely different way (and also have their place).

 

[onalaska]

Took a drive the other day and it was slow to warm up like the thermostat was stuck open. Picked up a 180 degree thermostat at Auto Zone. It looks like two bolts and a little coolant and it is in. The intercooler coolant pump ran for 3-4 minutes after shutting the engine off which was a surprise. I have never heard it running after shutting the engine off before until I took it apart and found a loose connection around the brush connection. I guess that is normal.

 

[standby-V]

Coolant

These cars take a special coolant, hope you didn't add normal coolant.

Took a drive the other day and it was slow to warm up like the thermostat was stuck open. Picked up a 180 degree thermostat at Auto Zone. It looks like two bolts and a little coolant and it is in. The intercooler coolant pump ran for 3-4 minutes after shutting the engine off which was a surprise. I have never heard it running after shutting the engine off before until I took it apart and found a loose connection around the brush connection. I guess that is normal.

 

[PTpro]

Engine hot - A/C off..Manufacturer bulletin to dealer to fix ECU bug! .

Left the house and got this message in the DIC about 5 miles down the road. Checked the gauges and the temp was on the left peg showing no temp at all. The engine fan running at high speed, but the radiator hose had no pressure on it at all and the engine was not hot. Checked the engine temp sending unit connector and it looked OK. Plugged in my scan tool and the engine temp. Was reading normal. Cranked it back up today and immediately had the same message on the DIC. Engine cooling fan on high. After running about 10 min the message went away and noticed the temp gauge was reading normal again. Engine fan turned off and it has been normal since. What happened? Loss of comm? From the ECU? Scan tool was showing normal temp. but the ECU thought it was hot even though the gauge showed it was cold. At least I know I didn't overheat the engine.

I had the same problem with my 2006 XLR-V and drove it to my dealer. The Service Manager told me it was a common ECU bug they were made aware of by the manufacturer. I'm glad checked out the problem myself first and drove my V to the dealer rather than having it towed like many others have had their V towed to the dealer when this happened! I asked them why they didn't fix my ECU the last time I was there for maintenance service and they told me they only update the ECU when owners have a problem. That kind of attitude really upsets me!

 

[David XLR-V]

Left the house and got this message in the DIC about 5 miles down the road. Checked the gauges and the temp was on the left peg showing no temp at all. The engine fan running at high speed, but the radiator hose had no pressure on it at all and the engine was not hot. Checked the engine temp sending unit connector and it looked OK. Plugged in my scan tool and the engine temp. Was reading normal. Cranked it back up today and immediately had the same message on the DIC. Engine cooling fan on high. After running about 10 min the message went away and noticed the temp gauge was reading normal again. Engine fan turned off and it has been normal since. What happened? Loss of comm? From the ECU? Scan tool was showing normal temp. but the ECU thought it was hot even though the gauge showed it was cold. At least I know I didn't overheat the engine.

Hey man, so glad you posted your experience with the engine hot - ac off DIC alert. THE EXACT SAME THING JUST HAPPENED TO ME. Detail for detail down to the 10 minutes after restarting the car after the first ocurance and the warning disappearing AND the temp gauge working again... Anyway, had to share. I have a 2006 xlr v (black, sick as heck!), and I'm hoping that is the last of that warning. Did the warning ever come up for you again?

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[PTpro]

Hey man, so glad you posted your experience with the engine hot - ac off DIC alert. THE EXACT SAME THING JUST HAPPENED TO ME. Detail for detail down to the 10 minutes after restarting the car after the first ocurance and the warning disappearing AND the temp gauge working again... Anyway, had to share. I have a 2006 xlr v (black, sick as heck!), and I'm hoping that is the last of that warning. Did the warning ever come up for you again?

Sent from my SAMSUNG-SM-G935A using Tapatalk

Read the original thread. This is a common occurrence. My 2006 XLR-V started to happen once a year since 2007. Many say it's an engine thermostat that sticks open occasionally and the sensor gives this erroneous message because the engine doesn't warm up fast enough. They say they changed installed a new thermostat and the issue went away. If mine doesn't disappear on its own, I have my mechanic reset the ECU code and it's fine again for a year or so. I'll have the thermostat changed if it starts happening too often. Don't let anyone tell you it's a bad sensor. That's a 6 to 8 hour job because of where it is located and extremely expensive to replace, especially when that is NOT the problem. Many dealers make huge money changing sensors when actually it's the thermostat.

 

[David XLR-V]

Read the original thread. This is a common occurrence. My 2006 XLR-V started to happen once a year since 2007. Many say it's an engine thermostat that sticks open occasionally and the sensor gives this erroneous message because the engine doesn't warm up fast enough. They say they changed installed a new thermostat and the issue went away. If mine doesn't disappear on its own, I have my mechanic reset the ECU code and it's fine again for a year or so. I'll have the thermostat changed if it starts happening too often. Don't let anyone tell you it's a bad sensor. That's a 6 to 8 hour job because of where it is located and extremely expensive to replace, especially when that is NOT the problem. Many dealers make huge money changing sensors when actually it's the thermostat.

Thanks for the advice, especially concerning the dealership potentially falsely diagnosing the problem as a sensor for a financial gain. As long as there is no harm to the engine. I'm not tripp'n on an occasional alert. I will still of course double check everything if I see this message.
Love this forum...

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[onalaska]

Hey man, so glad you posted your experience with the engine hot - ac off DIC alert. THE EXACT SAME THING JUST HAPPENED TO ME. Detail for detail down to the 10 minutes after restarting the car after the first ocurance and the warning disappearing AND the temp gauge working again... Anyway, had to share. I have a 2006 xlr v (black, sick as heck!), and I'm hoping that is the last of that warning. Did the warning ever come up for you again?

Sent from my SAMSUNG-SM-G935A using Tapatalk

Replacing the thermostat fixed the problem. Haven't had that message since the thermostat was replaced back in 2013. Replacing the thermostat is about a 20 minute job. One of the easier things to replace on the XLR. Have a new gasket and some Dexcool antifreeze handy to top off as you will loose a little coolant in the process of replacing the thermostat.

 

[Jerry11j]

Hot engine ac off

Just bought a 2006 V and got this message driving home. Found this webs and the forums and this issue. Changed my tstat and fixed it! Thanks for the guidance! Also found a thread suggesting to check the sc fluid. Wouldn't have known that. It was very low. I think the sytem is not dedicated and sc drained with the tstat.

Only difficulty was the radiator hose clamp. Googled a hose clamp tool and it helped a ton.

Great site guys!