ednja

I have a theory that the programming in the GM 3.4L PCM sets the cooling fan turn on temperature too high for the engine to cool properly. The thermostat is rated at 195 deg F, so the operating temperature shouldn't be much higher than 195 deg F. As far as I know, GM doesn't give a specification for the turn on temperature of the fans, but I've read from one source that low speed fan turn on is 208, high speed fan turn on is 230, and fan turn off is 203. When the gauge needle is pointing straight up (half way), the the temperature is about 212 deg F. When the air conditioning is turned on, both fans turn on at high speed. When the fans are in low speed, both fans turn on with low speed, but it's not enough to stop the temperature from getting higher, so to get both fans running at high speed, the temperature has to climb up to 230 deg F before the high speed kicks in and then it takes time for the temperature to drop down to the turn off temp about 203 deg before it begins its climb back up again. At about 225 deg, my transmission starts to act up by having jerky shifts from the excess heat, especially on uphill.

In the winter time, the engine coolant temperature on my van regulates very well constantly between 195 and 200 deg F. In the summer time, with the air conditioner on, it also regulates very well constantly between 195 and 200. But in the summer time, with the air conditioner off, it goes to the higher temperature. What would be wrong with the temperature regulating between 195 and 200 with the air conditioning off in summer? By my logic, there'd be nothing wrong with it. I think this could be another design flaw by GM that they dare not admit to because it's all about money. Meanwhile, the professional mechanics likely won't consider that the GM may have programmed their fan turn on temperature wrong. They'll change the defective parts, charge the big bucks for their labor and move on to the next one.
I haven't read anywhere on the internet about this idea, so hopefully I'll be seeing some feedback soon. Maybe my idea is completely wrong. But maybe it's not.

Ed

sergeimoskva

Hi !
Most likely you have a thermostat or temperature sensor is not working . Temp sensor is located by the thermostat follow the top radiator hose .
Read here ...Engine Cooling System - 2001 Chevy Venture

ednja

I changed both the thermostat and the temperature sensor, but still does the same thing. Do you own a chevy venture?
I like the link you shared. I've already been there and there's a lot of good info there. On that link, it's said that the low-speed fan on temperature is 220 deg F, hi-speed fan on temperature is 230 deg F, and fan off temperature is 220. That spec is even worse than the one I mentioned in my original post, and there's no hysteresis allowance for on/off. It's more evidence that GM may have their fan off/on temperatures too high above normal operating temperature.

I think you may have misunderstood my original post. I was presenting a theory about the GM 3.4L engine based on my observations of other people's problems with it and what I've experienced with my own 3.4L. According to the link you shared, the fans don't even turn on until 220 deg F and then switch to high speed at 230 deg F. My coolant temperature peaks at about 230 deg F, so it's temperature is normal according your link. However, other vehicle makes have the fans turn on at lower temperatures, so the engines don't run as hot as GM engines do. If the low speed fans don't turn on until 220 deg F, then for most of the year where I live, the fans won't even turn on during normal operation.

sergeimoskva

Hi !
Your first message I did not read carefully.
Now I understand what you mean.
I have a car Opel Sintra.
Car body and suspension - the same.
Is why cars Chevy Venture(1997-2004),Pontiac Montana(Trans Sport)(1997-2004), Oldsmobile Silhouette(1997-2004), Opel Sintra(1997-1999) - are similar
The engine of Opel Sintra 2.2l Ecotec 16V
In Sintra the thermostat now opens at the temperature of 92 C (197,6F)
Low fan speed is activated at a temperature of 102 C (215,6F)
The high speed of the fan is activated at a temperature of 112 C (233,6F)
For engine (3.4l) temperature 195F - this is good because the engine is designed and calibrated to run on a 195 and your gas mileage will be less.
If the needle on the scale did not reach the red line - the engine is operating normally and you do not worry.
Sorry for bad english

VentureForum

My analysis is that the ECU is programmed to run hot when the AC is off.
I measured this by reading the temperature off the ECU as well as separately measuring actual engine temperature and measuring the engine thermostat readout and watching how the system cycled.

This design to run hot is likely to improve the results of smog readings as these are typically taken with the vehicle entirely dependent on the fans for cooling.
Almost all smog tests would cause the engine to run near 130F during the test.
Running hotter would improve the smog readings in many cases.

The problem is that the engine then runs unnecessarily hot for many hours if your driving situation requires radiator fans for extra cooling.
This damages components, electrical connections, the ECU (which is under the hood fitted to the air intake for cooling) and anything not made out of metal.
All these components bake for some time after the engine is switched off, particularly the ECU.
This excessive heat could likely be the cause of much of the unreliability some people report.
Others may have a driving situation that mostly keeps the temperature down, i.e. cold environment and highway driving.

Fitting an override thermostat may violate smog requirements.
Adding after market fans with their own thermostat could be fine.

rce54

It looks like a switch could be installed for the driver to activate the fans at a lower temperature. The switch would just ground the dark green wire going to cooling fan relay # 1. That should operate the fans at slow speed.

VentureForum

Sounds right (I didn't verify you are correct). One step further would be a simple circuit to measure the temperature sensor and do the same thing. With a little processor, fancy things could be done, like adding an audible alarm if temp is out of range. I have a 1999 Venture to recover from heat damage causing it to fail smog. Other car makers doing the same trick. I helped my mechanic diagnose a Toyota V6. The problem was that the plug in connectors that get hot were all crumbling due to over temperature, turning into powder. The current components can't take this excessive temperature for long periods. This was a taxi, about 200k miles, think 2013 model so lots of slow driving and getting hot a lot. This is building unreliability into cars.
It's particularly bad for a Venture as the ECU is under the hood and also gets cooked. Other cars have the ECU inside the drivers cabin to run cooler.