160 deg. thermostat -- where ?

[mark henicle]

good news then we hope

I did finally fine the location in the manual of the sending unit and see about where it is. Oh my. No way with my size hands I can change it. Book says take the intake off. Not sure that would be enough either. Guess I will change the stat like you did. I still can't believe that is it. I am not going to attempt it for a couple of weeks, so if your symptoms come back can you let me know? Thanks

 

[mark henicle]

happened again today

temp about 39 on the way to work, around 15 minutes into the trip the gauge dropped to minimum like a rock.
P0128 set, fan came on again.
Drove for 12 minutes today at lunch, MIL didn't come on, gauge got to about 165.

 

[xlrlist01]

temp about 39 on the way to work, around 15 minutes into the trip the gauge dropped to minimum like a rock.
P0128 set, fan came on again.
Drove for 12 minutes today at lunch, MIL didn't come on, gauge got to about 165.

When the PCM sets a fault code, it does so based on an algorithm that suggests what might be wrong. There is a very high probability that something is wrong, but the one thing the PCM does not know is what is wrong. It does not have perfect knowledge, it is "guessing" based on a set of rules.

P0128 is a warning that the thermostat might be stuck open. It might also be that the temperature sensor is defective. Because the PCM does not know what is wrong, it is taking actions to protect the engine from damage, which in this case is a risk of overheating, hence fans commanded on. Fans on is a precautionary measure.

If it is very cold outside and you are running a thermostat that is opening at too low a temperature, you could get this code. You could get this code if the temperature sender unit is failing. You could get this code if the air temperature sensor is failing and there are problems with the cooling system (possibly wrong thermostat). You could also get this code if the PCM is failing, (though you would probably have other codes too). The key thing is that fault codes are diagnostic aids, they are not a description of the defect.

So, the question is, what is going on? Do you have one of those touch-less thermometers? It would be useful to know what temperature your engine (eg radiator hose) is at. Combine that information with what the Tech2 indicates the temperature sensor is reporting (and check the air temperature sensor while you are about it) and you have more information to help with the diagnosis of the real fault.

HTHs

 

[mark henicle]

well said. Matches the service manual

I do have a infrared temp tool. I will check it next time. I also do have heat in the interior when it happens. I don't have a Tech2. Appears to be an invaluable tool to have. Temps here today records setting, around 64. Doubt it would fail if I drove it today. Thank you. Mark

When the PCM sets a fault code, it does so based on an algorithm that suggests what might be wrong. There is a very high probability that something is wrong, but the one thing the PCM does not know is what is wrong. It does not have perfect knowledge, it is "guessing" based on a set of rules.

P0128 is a warning that the thermostat might be stuck open. It might also be that the temperature sensor is defective. Because the PCM does not know what is wrong, it is taking actions to protect the engine from damage, which in this case is a risk of overheating, hence fans commanded on. Fans on is a precautionary measure.

If it is very cold outside and you are running a thermostat that is opening at too low a temperature, you could get this code. You could get this code if the temperature sender unit is failing. You could get this code if the air temperature sensor is failing and there are problems with the cooling system (possibly wrong thermostat). You could also get this code if the PCM is failing, (though you would probably have other codes too). The key thing is that fault codes are diagnostic aids, they are not a description of the defect.

So, the question is, what is going on? Do you have one of those touch-less thermometers? It would be useful to know what temperature your engine (eg radiator hose) is at. Combine that information with what the Tech2 indicates the temperature sensor is reporting (and check the air temperature sensor while you are about it) and you have more information to help with the diagnosis of the real fault.

HTHs

 

[xlrlist01]

I do have a infrared temp tool. I will check it next time. I also do have heat in the interior when it happens. I don't have a Tech2. Appears to be an invaluable tool to have. Temps here today records setting, around 64. Doubt it would fail if I drove it today. Thank you. Mark

Any information you can add will be useful. Do remember that the temperature displayed on the DIC is not the temperature as reported by the temperature sensor, it is some value the PCM and other computers between them have decided to display. Under nominal conditions it should be the sensor's value, but as there is no direct connection you can't assume that it is always so. The way you report the value rising to start with suggests that the fault might not be the sensor, maybe that is a 60/40 sort of probability.

P0128 is all about your XLR taking too long to warm up (ie reach the reported water temperature of 160 degrees). How do you drive? If you are in very cold conditions and you are close to (but above) idle for a largish proportion of your journey then just possibly this code could set without there being a defect in your XLR (other than a fault in GM's P0128 algorithm). Seems a bit unlikely to me as if so others would get this.

 

[mark henicle]

better today

Temperatures were in the high 50's today. Drove it two times for at least 20 minutes each trip.
Temp on gauge appears to be around 190. After getting home used the touch less temp unit and checked the how water exit to the radiator and it was around 185. I guess I have to wait until it gets cold again. I do drive like a normal person, my wife's foot is heavy and she takes a shorter trip. to work is only 4 miles. Not sure how many out there are driving their beautiful cars when it is less than freezing out there. I do. Perhaps the old cardboard in front of the radiator is next. Will the tech2 store all of the important data just before the MIL light comes on? My light doesn't come on until the next start after the trip the gauge went to zero.
Thank you very much for your comments and education.

 

[xlrlist01]

From the description you have maybe got water getting past the thermostat. 185 is a bit low, the thermostat should open at over 190 and you should get closer to 200. Although, they way you are measuring the temperature and the accuracy of the touch-less thermometer do come into play, and how long it is since you switched off too.

A small clarification, for this use, the Tech2 is not storing any data, that would be the PCM. However, what is of interest is to compare what the PCM is reporting the temperature as being (as measured by the sensor) and what the touch-less thermometer is reporting. If they are within a few degrees, then I am suggesting that the problem isn't in the sensor circuit.

As you are driving normally, your XLR should be at a decent temperature within two to three miles. If you are driving slowly it might take a little longer. I have been out well below freezing and have had no difficulties with the operating temperature. Indeed, it is part of the joy of open top touring to have the heaters on max, the top down and outside temperatures far below freezing. To those who haven't done it, well you have gotta try it! Don't attempt to raise or lower the roof in low temperatures though.

Maybe somebody else could jump in here as I use a Tech2. I'm guessing that a reasonably standard code reader will be able to see the temperature the PCM is reporting. What I don't know is if a universal reader will display the sensor value as reported to the PCM, or if it displays the value the PCM has decided to report. Easy to check though, if you can borrow one and give it a try.

HTHs

Temperatures were in the high 50's today. Drove it two times for at least 20 minutes each trip.
Temp on gauge appears to be around 190. After getting home used the touch less temp unit and checked the how water exit to the radiator and it was around 185. I guess I have to wait until it gets cold again. I do drive like a normal person, my wife's foot is heavy and she takes a shorter trip. to work is only 4 miles. Not sure how many out there are driving their beautiful cars when it is less than freezing out there. I do. Perhaps the old cardboard in front of the radiator is next. Will the tech2 store all of the important data just before the MIL light comes on? My light doesn't come on until the next start after the trip the gauge went to zero.
Thank you very much for your comments and education.

 

[lextoy]

does this tstat also fit the base model XLR ?
mr gasket 6367

 

[mark henicle]

more on my 0128 code

The sensor is located on the back of the passenger side head. It's a tight squeeze between the head and the firewall, but you can reach it and unplug the connection if you have small hands. It's probably the thermostat though. I just had the same problem and picked up a new stat to put in this week.

I finally changed my thermostat, and I don't think that fixed it. First the 3 bolts that hold the stat cover on were slightly rounded, bet someone has been here before. Pulled stat out, it has some kind of rubber on top and bottom of the "valve" of the stat. Some of it is missing, guess in the radiator or system somewhere. I don't know what temp the stat is, only markings are STC and 1
00. Anyone have any idea the make and temp of it? I put a AC delco in that has a 180 degree spec. After idling for a half hour the temp barely gets to 160. I drove it a couple of cold days, and I really don't think it fixed it. I didn't get 128 code but temp gauge never got to 180. I guess I will see next year when temps get below 20 again. I really don't want to change that sensor, what a place to put it!

 

[hdduane]

If I read all of the posts correctly the 160 degree thermostat will make the XLR-V run better. My question is will it make the XLR Base run better? and do I need to have the ecm values changed If I go to the lower degree thermostat?

 

[lextoy]

its not necessarily going to make a stock car run better. its just gives you more room to stay cool when under heavy loads, like full throttle runs etc.
when you start adding high performance mods this becomes more important. as you are in AZ, it might benefit as you are driving in hot conditions alot more than lets say someone from montana. but beware. the northstar engine is designed as a hot running engine. running too cool can do damage.
it is best to bring the engine to operating temp BEFORE any hard driving. the aluminum block and steel sleeves will expand at different rates when heated, and were designed to perform best when both were properly heated up.
a Tstat probably isnt warranted on a stock car unless you are driving it really hard for prolonged periods in hot weather. if you go ahead and put one in, make sure its at operating temp before flogging it.