After replacing all coolant system components and switching over from OAT coolant to green coolant I have been getting a P0128 (Coolant Temp Below Thermostat Regulating Temp) trouble code. I think the coolant temp sensor is calibrated for OAT coolant and not green coolant. Has anybody had this issue? Can I recalibrate the coolant temp sensor with a GAP tool?

 

Wha?? Temperature is temperature. I would suspect a stuck open t-stat or faulty sensor. And why go away from recommended coolant? Did you do a water flush? Most green coolants gel up when mixed with the wrong coolant.

 

"Ethylene glycol possess superior heat transfer properties due to a higher viscosity and a high boiling point whereas Propylene Glycol carries a low toxicity."

https://www.alsglobal.com/en/News-an...low%20toxicity.

OAT is fine if you do not miss a service interval. If you miss a service interval, OAT will cause damage to the engine (Dex-Cool Lawsuit). Also, out on the trail or in remote locations, it might be difficult to find an OAT coolant.

Yes, I did a double flush with Prestone flush and one with just water before adding the new green coolant.

 

The t-stat maintains a set temperature by varying how open it is with a set rating for when it begins to open. So the coolant will not be the issue even if it "cools better". This will really on benefit a large engine under high stress and heat or something like a generator operating outdoor in a really warm climate. For a tiny 4.4 automobile engine, it will have zero affect. So again, temperature is temperature. Did you replace the coolant crossover tube housing? Like the entire thing which would include new sensors and t-stat? Because that is an often replaced component and only OEM is recommended for that due to cracking of aftermarket ones.

Also that is all old news and not even valid about the lawsuit anymore due to all the reformulations since then and even before really. OAT is easy to find as Dexcool and Prestone is carried all over the place. But I dont disagree that the green stuff, while potentially harmful to the Jag 4.4, is easier to find and some tiny corner gas station 200 miles from civilization. I just prefer to use fluids that match the required specs. And FYI, green coolant if not changed will cause issues too of course. The whole idea of fancy coolants is to prevent electrolysis of intermixed metals in a closed system, to prevent corrosion. The AJV8 is primarily aluminum in nature. But the fuel pump and coolant pipes are not all 100% aluminum. When green stuff breaks down electrolysis will uptick and the block will begin to corrode. Like you said though, it is all about maintenance. If people dont do fluid changes when they should, that is on them. But just want to point out, the green stuff is defiantly not safer at all in an engine that requires OAT. And frankly, it would still take some pretty stretched out coolant chance intervals to really be an issue.

 

The trouble code started almost immediately after replacing all coolant system components (except for the expansion tank) and switching to IAT coolant.

Ethylene glycol (IAT) has better heat transfer properties than propylene glycol (OAT). Obviously, the LR3's engine ECU is calibrated for OAT. I think this could be the issue.

 

So you did NOT replace the housing. And again…… temperature is temperature. Good luck.

 

Once again, all coolant system components with the exception of the expansion tank were replaced. Yes, this includes the thermostat housing assembly.

Different compounds have different properties, ethylene glycol (IAT) has better heat transfer properties than propylene glycol (OAT).

 

My manual says "Texaco XLC" which is orange, and ethylene glycol
I use spec and have 185k trouble-free miles (I do keep up on maintenance)

School me:
Does Texaco XLC = DexCool because "orange"?
You seem to want ethylene glycol, and DexCool is that - is it not?

I usually trust the spec because an LR engineer I am not
(Besides, I think the DexCool "issues" were a problem with the GM engine, not the coolant itself)

Does the CEL happen soon after startup?
Is your thermostat stuck open?

I wonder what would happen if you re-flushed and used the recommended spec?
Would your CEL persist, or vanish (if not a thermostat issue)?

 

Yeah, as stated previously, temperature is temperature regardless of coolant chemistry. A properly functioning thermostat is going to open at it's designed temperature, no matter the liquid it's circulating.
Even if a different coolant is 'better at cooling', after initial warm up, the engine will not (and should not) operate below the thermostat's opening set point unless the thermostat is stuck open (disregarding some sub-freezing weather edge cases).

But if your thermostat is stuck open then that's all beside the point. That's a fairly easy thing to check, as is the temp sensor. If you changed the thermostat housing, I'd guess you installed the new temp sensor they typically come with, so it could be either. Even if you didn't change the temp sensor, the old one could still be the issue too, of course, as it would have been disturbed during the t housing change over.

Ditto on going oem only for that housing by the way. Others have been known to be problematic, even more so than the oem one. Even oem parts can be defective out of the box, though, especially these days.

 

I've been running green coolant for 2 years since I got my LR3. No issues. The previous owner had switched to green. Maybe one day I'll switch it back but it's working fine.