When you measure the coolant temperature, check it at the upper radiator hose, not at the radiator. It should be around 195 there.
'I also check the Coolant Temperature In the radiator after it has been running for a while with a thermometer and it was also only reading about 160°f"
Clearly, OP already checked the temperature in the radiator, with a separate thermometer.
I’m going to “go out on a limb” here . . .
it’s apparent that the engine really IS NOT getting up to proper operating temperature
Therefore, P0128 is not a BS code. it’s being generated, because the engine really isn’t getting up to proper operating temperature in a timely manner. In fact, it seems it’s not getting up to proper operating temperature at all
This vehicle doesn’t have some unusual cooling system configuration, right? I’m assuming it is the same as most cars.
It sounds like you’ve done all the rights tests so for. And your friend is correct, that was a good test they suggested. The coolant it isn’t supposed to circulate through the radiator with the engine cold. It only circulates through the engine then. As the engine warms up the thermostat is supposed to open and maybe 5-10 minutes after starting a cold engine and then idling it, hot water from the engine will start to pour into the top of the radiator. The radiator cooling fan often comes on about this same time, so watch your fingers!
Depending on how the cooling system is configured, once the engine gets hot, often you can look into the top of the radiator (with the cap off) and see the coolant pouring in from the top hose. Suggest to repeat your friend’s experiment, only this time monitor to see if hot water starts to flow in at the top hose on the radiator after 5-10 minutes of idling.
If you can’t tell for sure by peeking through the radiator cap hole, you can remove the top hose from the radiator and put the end in a bucket. When the engine is cold, no coolant should come out from that hose. Next see if hot water starts pouring into the bucket after 5-10 minutes of idling.
I’m presuming your engine has a radiator fan, that only is supposed to spin when the coolant gets to a certain temperature. From what you say, it does this using a fan-clutch gadget. However it works, visually check to make sure the radiator fan isn’t turning when the engine is cold.
Besides checking the thermostat in a pot of hot water to make sure it opens and closes correctly, there’s a couple of other things that cause car owners grief about thermostats. First, there are two different kinds of thermostat. The normal kind, and the bypass kind. In most cases either will fit, but only one will work correctly. The type designed for your car in other words. Second, it isn’t uncommon for diy’ers to install the thermostat backward. The wrong orientation in other words. I’d guess this would cause overheating, not under-heating. But probably a good idea to get a second opinion on whether you’ve got it facing the correct way or not. At the same time, make sure all the proper holding brackets and gaskets are there so coolant can’t leak around the thermostat edges.
The O-ring seal must be missing from the thermostat if coolant is getting passed it at less than 195F.
While thinking about this I feel I’ve gone off on a tangent and retract my remarks. I might present the following theory though.
This is on the assumption that the thermostat is operating properly and opening at 195 degrees. It’s also predicated on an unknown as I’m not familiar with interchange on this model, belt routing off the top of my head, etc.
On small block Fords it’s possible to have the water pump operate backwards on an incorrect pump application or improper belt routing. This pushes the coolant back through the radiator and against the thermostat instead of vice-versa.
So. Any chance there’s a pump difference due to a change at one time or the pump drive belt is not routed right?
This engine uses an automatic belt tensioner, as far as I know
In my experience, if you’ve got the belt routing wrong, you won’t have the correct tension, and you’ll know it immediately
Either WAY too loose, and you’d be a 100% fool to think it’s okay
Or so tight, that you can’t even get the belt over all of the pulleys
I believe this particular engine used a serpentine belt setup, right from the start. Therefore, I think there were no changes, in regards to water pump direction of rotation
You’re quite likely correct. I’m just throwing something out there without researching the parts history and since the truck apparently had some work done on it. The thought of someone making alterations to belt routing, removal of the A/C part of it, or whatever came to mind.
It would be odd to get that many bad thermostats in a row but they’re easily checked as mentioned with a pan of water and thermometer on the stovetop.
I’ve tried to think of an oddity involving the possible use of an incorrect head gasket which could affect coolant flow but that is grasping a bit also.
Did tou check to see if the surface the thermostat flange mounts against is damaged or perhaps as was suggested earlier an o-ring is missing.
Someone could have put in a larger radiator. On my Chevy you can have 2, 3 or 4 core. If you look in the cap you can count the holes across from front to back. If you put your year and engine size in a parts supplier it should give you the correct radiator and hopefully a description.
The sensor I replaced was the ect sensor that is located I. The water outlet pipe just besdie the thermostat housing. I have asked autozone if there was a second sensor that controls a part of that system but they are telling me that ,the ect sensor is the only one I have. I will check the temp of the Coolant in the upper radiator hose today and I’ll let you know what I find out. I really appreciate all the help and advice I have received so far! Thanks
Just for the hell of it you could try blocking of half of the radiator with cardboard, to see if that brings the temp. up.
It’s a pickup so it has a larger radiator than a car would. So maybe don’t try to determine the size of the radiator. I hate to say there is a chance that things are normal, but you’ll never know until you check another S-10 of about the same type. The heater seems to be normal so I’m guessing that the rest of the truck is OK. It’s only a guess.
If you got your ECTS at AutoZone, that could be part of the problem. On some GM models, there were two ECTS available, one with a plastic tip around the sensor and one with a brass tip. The plastic tipped ones are known to cause issues. You should use a brass tipped one and you may have to go to a dealer to get one.
There are brass tipped aftermarket sensors as well and they should be OK, but the plastic tipped ones tend to predominate the aftermarket. GM also sell plastic tipped ones so if they try to sell you one, refuse it. I think you can specify a brass tipped one at RockAuto.com.
Re: Coolant temp sensors an engine might sport
I can’t speak to OP’s particular vehicle, but my early 90’s Corolla has 4 separate sensors that screw in and are immersed in the coolant path and measure the engine coolant temperature.
- used by the engine computer (called the ECTS);
- used for the dash temp gauge (called the dash temp gauge sending unit);
- used in conjunction with the cold start injector to inject extra gas on cold starts (forget what that one is called, “thermal sensor time unit”, something like that); and
- used in conjunction with a relay to turn on the radiator coolant fan when the coolant gets too hot (called the radiator fan temperature switch).
Newer cars tend to replace all four of these with just one sensor, and let the computer do the rest of the work. On a 99, you probably have the first two, I doubt you’ll have the third, may or may not have the 4th.
I could only find temp sensor that feeds the ECT and PCM.
Yes coolant does circulate even when the thermostat is closed, it passes from the engine to the heater core and then back to the radiator.
Late on this thread but I’m getting the same problem on my 93 Toyota pickup 3vze. Did you end up figuring this out? Sounds to me like you had faulty wiring going to the coolant temperature sender(sends the signal to your dash temp gauge) if everything else was replaced properly.