p0128 Engine temp below thermostat temperature/ strange O2 sensor values

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bhullIT

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2004 Escalade with the same issue.

Just changed the thermostat because engine was not heating up. Now the temp does rise, but it takes a while and does not reach 187F (dash gauge remains below the middle mark between 160 and 210 and cabin heat delivery is poor).

Many posts suggest the dash gauge should read 210F but the OEM operating temp is 187F. Would someone be able to clarify?

Why does the cooling system even matter if the engine temp is lower than the thermostat set point? I'm assuming that the thermostat remains fully closed until the temp rises & until then the cooling system is not at play (the thermostat, and only the thermostat, regulates the engine temp). The fans and other parts of the cooling system just ensure cooling capacity, but not access. What am I overlooking here?

Does the thermostat always allow some flow (significant enough to cool)? Is there another pathway to the cooling system?
 

Doubeleive

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A good wild a$$ guess, well done.

But the propane system is perfect adjusted to the engine and at least it is technically very simple. The normal PCM is used, no tune at all.

The fuel injectors signal is just routed over the propane controller, and this controller decides, based on if i drive on fuel or propane, if the signal is just passed to the fuel injectors, or converted and send to to the propane nozzles. It must be converted, because the amount of propane is different to fuel, so the opening time for the propane nozzles differ from the calculated fuel injectors time.

The PCM does not know anything of the propane system, so to speak.

The PCM use the O2 Sensors, the mass air flow sensor and all other engine parameters like running on fuel. If i drive on gas, i can switch just with a push on a button to propane and opposite. My car behaves exact the same. You feel no difference.

And also the temperature behave, does not change at all.
I would try a old school fix and place some cardboard over 1/2 of the radiator, then go drive it and monitor the temp, if it starts to get too hot instead of normalizing in the center then you can remove some cardboard to get it right. that will also confim if it is "cooling system" related.
 

Doubeleive

Wes
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2004 Escalade with the same issue.

Just changed the thermostat because engine was not heating up. Now the temp does rise, but it takes a while and does not reach 187F (dash gauge remains below the middle mark between 160 and 210 and cabin heat delivery is poor).

Many posts suggest the dash gauge should read 210F but the OEM operating temp is 187F. Would someone be able to clarify?

Why does the cooling system even matter if the engine temp is lower than the thermostat set point? I'm assuming that the thermostat remains fully closed until the temp rises & until then the cooling system is not at play (the thermostat, and only the thermostat, regulates the engine temp). The fans and other parts of the cooling system just ensure cooling capacity, but not access. What am I overlooking here?

Does the thermostat always allow some flow (significant enough to cool)? Is there another pathway to the cooling system?
should start your own thread, but normal operating temp is around 195-200 roughly it is always flucuating a little bit not enough to see the gauge wiggle but the gauge should normally remain stationary for the most part once it has heated up. different conditions can make the gauge move, elevation, towing, engine load, etc.
I would suggest maybe watching some youtube video's on it to get a better understanding. the sensors need to be a certain temperature to provide correct data to the computer to calculate air+spark+fuel for economy, otherwise stuff just doesn't operate as it is was intended.
 

bhullIT

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2004 Escalade with the same issue.

Just changed the thermostat because engine was not heating up. Now the temp does rise, but it takes a while and does not reach 187F (dash gauge remains below the middle mark between 160 and 210 and cabin heat delivery is poor).

Many posts suggest the dash gauge should read 210F but the OEM operating temp is 187F. Would someone be able to clarify?

Why does the cooling system even matter if the engine temp is lower than the thermostat set point? I'm assuming that the thermostat remains fully closed until the temp rises & until then the cooling system is not at play (the thermostat, and only the thermostat, regulates the engine temp). The fans and other parts of the cooling system just ensure cooling capacity, but not access. What am I overlooking here?

Does the thermostat always allow some flow (significant enough to cool)? Is there another pathway to the cooling system?
Thanks to all the helpful advice and suggestions! Forums are awesome & those who share make them awesome!

As mentioned above, the OEM rad has a flow restrictor in the overflow port but an aftermarket one may not. Apparently there is a TSB on this.

So, although the thermostat remains closed, there is some flow through the rad to the overflow reservoir and back. In cold weather, this 1/2" unrestricted line flows enough to keep the engine cool, but too cool.

When a vehicle runs too cool either the thermostat is stuck open, or there is another path for coolant to reach the cooling system (thus cooling the engine).

It's only for overheating that one would also consider other components of the cooling system including the water pump, sensors, and fan etc.

My initial solution was to install a faucet cone washer/restrictor in the 1/2" line near the reservoir inlet, BUT although it helped, the temp did not rise fast and high enough for my liking as it's going to get much colder.

My next solution seems to work fine. I drilled a 1/16" hole (quite a small hole but, from what I read, it's what the OEM rad uses) through the sealed end of a 1/2" plastic alloy PEX plug and inserted it INTO the line. I was quite pleased that the OD of the head of the plug was a perfect fit for the line.

Now the engine heats up in reasonable time and remains just below 210 on the gauge.
 
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2015TahoePPV

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I have the problem since the beginning and i don't now if the cooler was replaced by the former owner..
I can’t fathom the thermostat sticking “open” causing the engine to never get to temperature. I think it would get there eventually. In my case, the gauge was showing no movement whatsoever, and I drive 75-80 for half an hour each way to work. I also had hot heat in the cab, so I’m confident the engine was actually at its normal temperature range.
 

rockola1971

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I can’t fathom the thermostat sticking “open” causing the engine to never get to temperature. I think it would get there eventually. In my case, the gauge was showing no movement whatsoever, and I drive 75-80 for half an hour each way to work. I also had hot heat in the cab, so I’m confident the engine was actually at its normal temperature range.
Thermostat sticking does just that, overcools the engine and it never gets to its roughly 200deg normal operating temp range. This is the magic number roughly that is required for the engine to warm up too before the PCM will go into closed loop where it actually pays attention to the various engine/exhaust sensors. The engineers figured out after many years that most engines can perform better for emmissions and MPG if they are ran around 200deg. You get more complete combustion because the cylinders are hotter than the OG setups. My old vehicles I had many years ago with Gen 1 sbc would run around 185 or so. If they got to 200deg, there was a problem and better be finding a place to park and figure it out before you cracked a iron head or the block!
 
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nonickatall

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So, I've finally gotten around to taking care of this problem.

Yesterday I built a orifice that I installed in the hose to the cooland reservoir. With the recommended diameter of only 1.5 mm. This made no difference at all on two longer trips. Which means, I assume this isn't my problem.

Of course, I don't mean to say that this isn't the problem in other cases, but I looked at the exit of my cooler and there is a narrow orifice in there, that has a maximum diameter of 4 mm. I couldn't measure it that precisely. But with a really small passby it makes absolutely no difference.

Based on human judgment and the way the cooling system is designed, this can actually only be the thermostat.

I'm surprised that I had this problem with the old thermostat. Then I installed a new one and the problem hardly changed. Of course it could be a coincidence that the other, new thermostat is stuck in the same way as the old one.

I have now simply ordered a new thermostat and will replace it again.

I will report...
 

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2015TahoePPV

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So, I've finally gotten around to taking care of this problem.

Yesterday I built a orifice that I installed in the hose to the cooland reservoir. With the recommended diameter of only 1.5 mm. This made no difference at all on two longer trips. Which means, I assume this isn't my problem.

Of course, I don't mean to say that this isn't the problem in other cases, but I looked at the exit of my cooler and there is a narrow orifice in there, that has a maximum diameter of 4 mm. I couldn't measure it that precisely. But with a really small passby it makes absolutely no difference.

Based on human judgment and the way the cooling system is designed, this can actually only be the thermostat.

I'm surprised that I had this problem with the old thermostat. Then I installed a new one and the problem hardly changed. Of course it could be a coincidence that the other, new thermostat is stuck in the same way as the old one.

I have now simply ordered a new thermostat and will replace it again.

I will report...
was the old thermostat actually stuck open? I’m still having a hard time imagining GM designing a cooling so efficient that the engine won’t reach operating temperature if the thermostat is stuck open. GM is famous for underengineering things, and I’ve been wrenching on them for over 40 years, so I’m confident in my skepticism, lol. I’m tempted to take the one I just replaced and gutting it and trying just to satisfy my skepticism.

Have you changed the coolant temp sensor? Mine always ran between 165 and 210, exactly in the middle between the two. This year then the winter hit, it didn’t read anything. Sometime it was intermittent (you could see the needle moving). These are mechanical thermostats, you’re not going to get a variance like that while you’re driving down the road.

It was <$20 for a Delphi one, might be worth a shot.

Good luck!
 
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nonickatall

nonickatall

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So now I finally fixed my problem.

Today I received my new thermostat. It is a Motorad which was one I could get in Germany without ordering at Rockauto, with this always extended shipping cost to Germany.

First when I removed my old thermostat I took both and put them into a pot of cold water on the oven and heat it up, until it reached 100 degrees Celsius which are around 210 Fahrenheit. I saw that both thermostats open mostly at the same time, so i put some cold water into the pot to lower the temperature. And I saw that both thermostat's start to close, the new one a little faster, than the other one.

So I finished my car with the new thermostat and made a test drive. The temperature raised fast, but stayed below a quarter, which you can see on the photo. The only difference was, that the temperature now was stable below that quarter.

But still much to low.

So I thought about my next step and i thought probably I should change the temperature sensor. I knew roughly where it is located, so I wanted to check for corrosion first, so I removed the connector and put it several times back on the sensor.

Then I started my engine and look at that my temperature. No it was 2 mm below middle.

So finaly, I changed two times my thermostat, thought for hours about, what can be the problem, for this corroded connector in the sensor...:emotions122:

Aaaaarrrrrghhhh

But anyway, that means my engine never was to cold, it was just the temperature sensor which gave me a wrong temperature at the gauge.

It seems that this temperature sensor is also used by the ecm, what explaines the error I received, recently about the too cold engine temperature.

I think when the engine temperature is not measured correct, the values of my fuel injection must as well be a little bit apart.

But let see it positiv.

I learned a lot about the cooling system of my truck. I now have a thermostat which keeps the temperature more stable and the bad feeling, that I do something not good to my engine, while driving with a too low engine temperature is gone... And probably someone in the future will help this, before loading the part canon...

:cool:
 

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