Please don't turn this ugly because I really want to find out why us LT1/LT4 owners complain of too hot temperatures. Or in that some have a problem with it and some don't. I may either be on to something or just blowing smoke, but I want to find out if my hypothesis is right by returning some things to stock and trying a different approach.

It always makes me wonder how some can say they don't see it as problem or feel it as a problem when others including myself felt it an unlivable situation.

Here goes...

Does the Hypertech programmer have the ability to adjust the fans on/off temps independently of anything else? Meaning you can change the fan control and nothing else along with it?

Reason I ask is because I'd like to experiment for myself with the fans at stock settings. Because like I said in other posts my digital gauge always read much lower than my analog gauge. When the digital was at 230 the fans did come on but the analog was pegged! That’s too dam hot for me. Something about this always seemed wrong but I figured that was because the senders were in different places.

I could never understand why GM engineers wanted to wait until the temps were at 260 on the analog gauge to turn the fans on. Why they didn't use that sensor's (analog) location and data to control the fans since it was always higher than the digital? Through some reading about the system I found this to NOT be the case at all. They did want the fans to come on at 230 and the digital gauge should actually read (if it's working properly) higher than the analog gauge. Causing the fans to come on BEFORE the analog gauge got to 230.

The reason for is that the analog gauge is essentially reading cooled water directly from the radiator. The digital gauge reads not only water entering the system but also water mixed in from the bypass which would be hotter than the head water directly from the radiator and nothing else.

So the engineers did get it right, they wanted to turn the fans on before the head temps were 230.

I really didn't think 230 in itself was too hot (maybe a little) to turn the fans on but the heat emanating from the engine compartment was unbearable, working on the thing hot was impossible because you'd be knocked over from the heat. Comparing that to my other cars was like night and day, they are also newer GM cars and they didn't exhibit the same hellishly hot symptoms or gurgle when you shut them off. So figured I needed to do something or this car wouldn't last long. Therefore I did the 160 t-stat and fan reprogramming routine.

Through another long thread about all this a light came on about these sensors not being accurate. But it was too late in that thread to explain these thoughts because the bash fest had begun and nothing was getting solved except me taking a verbal beating.

With the Hypertech maybe I can return the fans to normal operation, reinstall the 180 t-stat, check the temp readings with a new sender for the PCM, the one in the water pump. Then see if the gauges more closely resemble each other, or the digital reading just a bit higher than the analog. If they do and the fans come on when they're supposed to I could probably live with it and let the system operate as intended by the engineers.

If it turns out to be the case that these senders are just getting way off maybe we can put this whole LT1 cooling issue/debate to rest.

 

ALLT4,
I can't answer your question about programming just the fans but I have not had my coolant gurgle in the overflow tank. Your sensors could possibly be out of calibration and sending or not sending false info. You may want to take your car and have the system checked to see if the sensor, guages and fans are working properly together. Let us know what you find as I feel sure that others would want to know if possibly their sensors make not be working too. Good luck!
Bernie

 

From what I remember, yes. But there are set on/offs for the 160* and 180*.

Why not just purchase LT1 Edit, then you will have the ability to set the fans on/off at any temp. Also, as much work as you've done and probably will do to your car. LT1 Edit would come in handy on the retunes.

 

The problem with me and testing these things out on my car is it's OBDII, things are not easily changed from stock and then back to stock many times for tests.

I don't have the cables, software or even the Hypertech which is still like $400.00

That's a lot of money just to try something. I could buy a new (on the WP) sender and see if it shows higher temperatures than what I'm used to seeing on the digital gauge.

That would be the only way I would know how to verify if the sensor is out of whack. The PCM temperature sender uses a two wire sensor, and I think the PCM assigns temperatures to different voltage outputs from the sender. I also believe it's a 5 volt reference.

Unless I could find out what temperatures the PCM assigns to different voltages from the sender and what voltages should be output by the sensor in relation to actual temperature I'm in the dark.

All I know is that the two senors shouldn't read temperatures THAT far apart, a few degrees I could see but not a 30 degree difference.

And that's exactly what happened with me and it sounds like others also have the same dilemma.

If it wasn't so dam cold out I'd take that sensor out and see if it has a build up of corrosion on it. I'm thinking since these cars are aging this might be the case, maybe the build up is insulating the sensor from sensing the correct temperature. Causing it to read lower temperatures than what they really are.

It's all speculation at this point but it would explain a lot things, certainly why a lot of us think 230 is too hot. It probably isn't too hot when functioning correctly but the heat we feel and observe tells us differently.

 

??????They didn't!! at least not on a 1996 LT4 or LT1..........where did you get this idea....it is INCORRECT!

Also the digital and analog gauges on my LT4 agree quite well....the analog gauge is difficult to read with any degree of accuracy....

 

Geeze, read the rest of that paragraph. I know they didn't want to wait that long for them to come on.

Here's the rest of that paragraph...
With the system operating incorrectly that's what one would be led to believe. If I had never looked at the ECT temp and only the analog gauge I would have believed the engineers designed a system to start cooling at 260. Again, I know this now to NOT be the case.

Thank you for confirming my suspicions though, your ECT sensor and gauge read pretty close to each other. Mine are way off, I believe my ECT sensor reads too low in relation to actual temperature causing the fans to come on too late, so late that the analog gauge is at 260.

BTW, I did find in the service manual what the resistance of the ECT should be at different temperatures. When I get ambitious I'm going to pull it and check its resistance readings at different temperatures against my Fluke's temperature probe.

 

It is important to keep in mind the LT1/LT4 is a "reverse flow" cooling system.
The coolant, from the radiator, goes to the heads first (where the analog sensor is) and then down through the block (picking up more heat) back to the water pump (where the digital sensor is).
Since the coolant is the coolest coming from the radiator and going to the heads and this is where the analog sensor is, how could the analog gauge read higher than the digital reading?
I suggest you get a infrared temperature measurment instrument and measure the temperature at the head beside the analog sensor and then at the digital sensor in the water pump. There should be "no way" that the analog gauge temperature is higher than the digital temp -- unless you have air trapped in the system and there is really an air pocket trapped in the heads instead of coolant. Or, your sensor/gauge is defective. As a previous post said, the analog gauge is not really that accurate and it is non-linear.

In fact, the advantage of a "reverse flow" cooling system is the fact the heads are cooler than the block preventing detonation in the heads while keeping the cylinder bore hot for decreased ring friction.
I'm not trying to start an argument, but this is a known fact of reverse flow cooling.

Tom Piper

 

My analog guage has read ~10* higher than the digital gauge, since the car was new.

 

http://www.theherd.com/articles/lt1_cool.html

One other thing:
Never, ever, ever run an LT1/LT4 without a thermostat or with a thermostat out of a conventional small block -- that is counter productive in an LT1/LT4.
I've seen where some have done this in an attempt to lower temps.
This may work with other engines, but not with the LT1/LT4.
The reason is the "two way" thermostat mentioned in the link above.


Tom Piper

 

The correct fan operation for a 1996 per the GM Service Manual..

"the PCMwill cammand low speed fans ON at 219F and OFF at 207F and, high speed ON at 228F and OFF at 214F"

also the fans in essence run always when the A/C compressor is on...

 

I didn't like waiting for the auxillary fan to kick on in stop and go traffic in the hot summer at that high temp. Even though my '96 LT4 has the stock 180 degree thermostat by programming with my hypertech to 180 setting changed temp aux fan came on to 213 which seems perfect so under normal driving conditions the aux fan never comes on. My digital and analogue gauges always seem close.......the LT4 Hypertech 3 manual says stock cooling fan temp "Fans on/off at 240f/225f the 180 setting 213f/205f and the 160 setting 192f/185f..........

 

Review of this forum will find many threads focused on this topic. It's obviously an issue for many, as it was for me, until I fixed it.

My Hypertech III manual says that it can indeed address ONLY the fan temps but when I tried this, my car ran very poorly and even backfired when I tried to start it. So I had to load the fully Hypertech Tuning Program and was sweating the time until I started the car and it ran smoothly. I suspect my car had a custom tune in it already and the Hypertech overwrote that with a true stock program based upon the VIN and the car didn't like it.

I see that many think that a 160 thermostat will force the car to run at 160 but this is not the case. The thermostat only just begins to open at 160 and is not fully open until 175 degrees. The car runs about 10 degrees hotter at 185 (PERFECT!!!). According to the Hypertech manual, a 180 thermostat starts to open at 180 and is not fully open until 200. I believe if the rest of the cooling system is strong, the 180 should keep the car running around 200 - 215. Which is ok to me but my car ran much higher. Now, the 160 keeps it where I am more comfortable.

The Hypertech manual says the fans cut on at 176 and go off at 166. Can't say much for the theorists but from experience, this simple mod made my car run cooler --- much cooler....

By the way, I bought my Hypertech III on eBay for $97.

Billy

 

I'm interested in your comment on LT1 Edit to modify the fan settings. Can you tell me more about this? Thanks....

Billy

 

Yeah Tom, I fully agree with all you said, I know all of this and it's the reason I'm starting this thread. Mine acted completely opposite of what it should act like. So bad in fact the analog would be at 260 then the fans would come on because only then was the digital or ECT sensor at 230.

I have a feeling more LT1 owners are experiencing the same condition while their cars age thinking the cooling system isn't working correctly. Really it isn't but it doesn't have anything to do with the thermostat being too high for the car or the radiator clogging. The fans are just coming on way too late because the ECT sensor is falling way out of calibration. It'll just get worse and worse with time.

If all you ever look at is the analog gauge you will think "those dumb engineers, waiting until 260 to turn the fans on"

I have an infrared temperature sensor but I'll have to wait until this summer to try all this out. The car is stowed away, I can get it out but would rather wait for warm weather.

I have NEVER seen my fans come on at a lower temp than 230-228 when stock, if they were supposed to then I have another problem to look into. They would run if the AC was on.

 

Personally, I never look at my analog gauge; I just read the digital temperature gauge.
I don't trust the analog -- either in resolution or actual reading.

The ECM reads the digital sensor and so do I.

If the analog temp gauge stopped working, I probably wouldn't know it for about a month.


Tom Piper

 

If you have a 1996 this is the correct operation........not the same for ALL C4's

Also if you have a huge descrepency between analog and digital readings you have a problem....

Good luck....

 

Yes you can, That is all I did to mine just to get the temps down a bit. I forget what the settings I could choose were? But it runs at about 200-210 now vs 230 range.

 

Yeah, no kidding. I wish I had known a little more about the system when I first bought the car. This would have thrown up red flags right away.

I had dam near a 30 degree difference, the ECT being the lower of the two. You can see how this would cause high temperatures.

BTW, I installed a new radiator right off the bat thinking it had to be bad but it changed nothing, and bled the hell out of the system with no change.

Personally I kind of like it, with that one you know what your head temp is, sort of, because it is a little unlinear. If I had never kept an eye on that one I'm sure I would have blown a gasket. When it used to go to 250 I'd turn the AC on in an attempt to bring the temp there down.

 

The CTS (Coolant Temperature Sensor), I think this is what you mean by ECT, is in the coolant pump. It is a thermistor that the ECM and digital readout use for sensing the coolant temperature.

Your statement tells me you believe the analog gauge is correct, but the digital gauge is incorrect.
I'm not saying you are wrong; but, on what do you base that assumption?

If any gauge is wrong, I believe it is more likely the other way around -- the analog gauge is wrong and the digital gauge is correct.

If both gauges are correct and you are interpreting the analog gauge correctly (which I can't because it is non-linear and not highly accurate), you have to have a problem in your cooling system, because the heads get the coolest water first and the CTS gets the coolant after the coolant picks up heat from the heads and the block.

Tom Piper

 

99% chance that you have a bad sensor and/or display. The other 1% is that you have a serious cooling system problem.

Reprogramming fans or changing to a cooler thermostat will fix neither problem, it will be at best a band-aid.

Which I think, after all the verbiage, is what you said.