Wow, thanks guys a lot of good information here. I had done a coolant flush and fill this spring including draining the block and used distilled water and Prestone extended life antifreeze and did add a bottle of water wetter.

Looks like I have a lot of things to check this weekend to see if I can restore cool running.

 

Hmmmm.........I think you guys have found the problem. after getting the car warmed up with the needle just about to the middle, I popped the hood and the vents are still closed. I am getting ready to check and see if the fuse is popped or corroded. If the fuse is OK, what do I need to check to get this functional?

In the meantime I will just zip tie in the open position.

 

If you're gonna open and zip tie, be sure to pull the fuse.

 

Update. Most of the time the car seems to run just right. It is not until the car has been running for over an hour that things start to heat up. Again, never above the top white line, but getting close to it. Now I did some trouble shooting this weekend and found that both fans turn on, the fans engage when the AC button is turned on, and the cooling vents open to the appropriate 30 and 100% positions when jumpered with a wire on the plug I pin 7&2 and plug I pin 7&1.

Did some further volt/ohm meter testing and found that on measuring pin 1 of plug II and pin 7 of plug I (temp sensor pins) while the engine was cool showed infinate resistance. The value should be around 2000 ohm in a ambient temp garage of about 75 deg. I did not check when warm, but I am guessing that my temp sensor is shot?

This would be the Temp II sensor on the front of the intake, correct? I wanted to check the sensor itself next. It will just unscrew? I then can submerge in icewater and check resistance from one wire to the threads, correct? And then heat up and check the value again?

Would a non-functioning temp sensor keep the cooling flaps from opening to 100%? Because it seems like even when the temp is running around the middle of the gauge a look under the hood shows the flaps not opening past 30%.

Thanks

 

It looks like the radiator cooling temp sensor is bad. This sensor is located at the lower front drivers side of the radiator. This sensor is supposed to turn on the fans when the temp goes above the middle of the temp range. (TheTemp II sensor in the intake manifold is connected to the fuel injection computer and does not control cooling.). The normal resistance of the radiator sensor is about 20 kohms? If it is infinite resistance, then it is probably bad. It has a two-prong electrical connector and is reachable (barely) with a socket. They cost about $50.

Hope this helps. I went through my cooling system recently and had a similar problem.
David

If you are driving along and the temp starts to increase, try starting the fans manually by turning on the A/C. The engine temp should drop. This would indicate that the radiator temp sensor isn't working.

It sounds like everything else in your system is OK.

 

Not to steal a thread, but my1991always runs at the last white line once it's warmed up. Should it be running lower?

 

My foggy memory says normal operating temperature is approx. 195 degrees F which is about at the 2'nd (or last) white line.

 

That is interesting, because my fans do kick on at near the second white line. Maybe I am overreading and the car is behaving normaly.

Just looked a little closer at the WSM and it states that the cooling flaps stay closed until 175 deg F, then they open to the 30% level, at 185 deg they open the rest of the way to 100% and stay that way until the car cools to about 175 deg F at which point it goes back to 30%.

I am still going to have to examine the temp sensor as the ohm meter seems to indicate that it is faulty.

 

please open the flaps and pull the fuse, you can open the flaps manually by turning the wheel at the end of the motor after you remove the rubber motor cover

 

Yes, I have considered doing this, but I would rather restore normal function it possible first. I will replace the coolant temp sensor and see if this makes a difference. If everything is working properly, I don't want to screw things up by forcing the car into a mode that it was not designed for (ie running too cool most of the time)

I do appreciate everyones input. Thanks for your patience with me while I try to sort things out in my head.

 

Your not going to hurt anything by removing the fuse , and your not going to know when the flap system decides to stop working ( IE decides to close ) as it should until the red warning light comes on when your sailing down the freeway.

If you note the later cars are now not equipped with the flap system, as I has caused many other problems if the system isnt working 100% all the time, its usualy either the controller computer or the relay or one of the sensors that give the system false info and with this the flaps will close , I had my set close in the middle of the summer on the freeway with AC on it took only a minute for the coolant to get into the red zone and the warning light to come on.
Remember the car is 20 years old and some of the elex systems arent able to work like they should usually due to bad solder joints or dirty connections between the parts. Pull the fuse

 

Thanks Mrmerlin,
This is the kind of reassurance I needed to make this kind of change. I am thinking that my flap function has likely been intermittant. I just didn't want to do the bandaid thing and ignore an underlying problem. I for sure do not want to someday be one of those "damn POs".
Anyway, thanks for the input.
Steve.

 

As relates to this subject, "one of those damn POs" would be someone who breaks/hacksaws out the cooling flaps.

 

Well Dave, if you look at it another way, pulling the flaps out is really upgrading to the the newer version, IE NO flaps..
I think its just as good to pull the fuse and then screw the motor **** to open the flaps, and then you wont have any surprises. The coolant temp will go up fast once the flaps close and things are at temp as there will be virtually no cooling air being passed through the radiator... BTDT.
I have cleaned the contacts on my 88 and the flaps seemed to work OK for a while then all of a sudden the temp goes wayy up when its usually riding at the lower white line, it only takes less than a minute for this to happen once the cooling air is cut off. Open the hood and sure enough with the A/C on, OAT at 80 deg. and about 1 hour of heat soak in the engine compartment the flaps are closed. keeping the hood open helps while the car cools off and the throttle is run at about 2000 rpm

 

Hmmmmmmm ........... There's an idea. Although I'm thinking I'll make it easy on myself and use a sawzall.