dyeager535

Have an '88 TPI setup I'm working with.

Trying to keep it as 'stock' as possible.

Secondary fan is on seperate relay, turns on with temperature switch alone.

I can't get the primary fan to work when I think it should. Getting ready to fire up engine for the first time, want to have cooling system up to par.

Manual says that if ECM sees over 223*F the primary fan should turn on.

With key in run, (engine off obviously) if I jumper the coolant sensor and check the scanner, coolant reads 304*. The fan doesn't work. If I ground "B" on the ALDL connector, without the sensor jumpered, the fan turns on. That test I believe proves all wiring is correct. (although I have thoroughly tested the wires, relays, etc for continuity, proper voltage, etc) The wire the ECM grounds for the primary relay in particular has no breaks in it, and is not shorted to ground, etc. I checked the contact for it at the ECM (prior to grounding pin B) nd made sure it was clean/good.

Watching the scanner, the ECM isn't commanding the primary fan on when temp is reading 304*. Interestingly enough, if I jumper the AC pressure switch, the scanner shows that the primary fan is commanded on, but it still isn't running.

Comparing the coolant sensor reading with MAT (no coolant in engine yet) the temp readings are very close in the scans, so I don't see there being a problem in the coolant sensor wiring either.

Not showing any codes from the scans, get the CEL when I turn the key, and it will spit out a code 12.

The manual doesn't state anything about the engine needing to run for the primary fan to work. That's the only thing I can think of though, as to why I can't get the fan to turn on, short of grounding terminal B as the manual states.

I'm not asking this as a cooling system question, just showing all the data I have, in an attempt to get a good answer about whether the ECM looks for the engine to be running for the fan to work.

RBob

iTrader: (1)

No need to worry. That ECM/mask will turn off all outputs unless the engine is running or it is in diagnostic mode. Most of the f-body GM stuff is this way.

RBob.

dyeager535

Thanks for the reply Rbob!

You were right, no need to worry.

Fired it up for the first time today, never got above 204*.

Sometimes "simple" info like this is hard to find. Thanks again.

jac113

iTrader: (4)

Hey dyeager, r u running a cooler t-stat than 195 or r u seeing a temp of 204 while driving? I ask because my with a practically new cooling system my car will warm to 222 and will cool to 214 with fan at idle. I always hear of cars running cooler and I'm kinda wondering how. At the same time I don't know what my car truly runs at becuase my Gage is off. Maybe my car will be cooler with air being forced through the rad while driving. I've always had cooling problems til now so would love to see Gage west of the 220.

dyeager535

I run stock t-stat.

As I recall, your temps sound about right for the stock fan. The manual I believe is wrong at 233* for fan "on", in PROM tuning I believe the actual bin is quite a bit cooler, nearer what your numbers are.

Need to take it on a cruise and see if your engine comes down to the temp your thermostat is rated for. If it does, your gauge isn't off, not sure how you know it is, perhaps it is, I just don't know how you arrived at that conclusion.

jac113

iTrader: (4)

dyeager,
I say my gage is off because when I finished the head gasket job the gage climbed to 230 + at idle and then I shut it off. I have a new rad, 195 t-stat, pump, cts and cap. I run 50/50 coolant. My timing is set right at 4-6 btdc. Prior to the repair the car always ran hot, combo of bad head gasket or having no air dam. Whatever the case I now have new gasket, rebuilt heads and gonna install the dam tonight.
To answer your ?, the gage is off because I put it on a scanner and traced the temp. It peaked at 222 when fan turned on and valleyed at 214 with fan off. The gage was about 20 degrees behind on the warm up and went 20 over when warm. I cleaned the contact hoping that caused the misreading. The gage was fine before because when it read 250 ish the cooland was boiling.

I'll look into a new gage after I run it with the air dam. I did a little city driving without the air dam and it peaked at about 230 which is probably normal, confirmed that by hearing the fan come on. I hope the air dam will get me closer to t-stat temps. Having done the head job myself, I find myself looking at the temp gage a whole lot more often. I also don't like the car running that hot so i'm going to look into changing the switch and therm to keep it under 200.

dyeager535

I hate to say it, but I have so little experience with these cars and their cooling system, I find it hard to believe that GM ran them that close to the ragged edge of cooling that they run that hot with just the air dam missing. But in watching other posts, I realize they can tend to run pretty hot.

Forget about changing the thermostat to keep temps down, it isn't physically possible. If the engine overheats with a 195, it will overheat at anything below that temperature. You are exceeding the capacity of the cooling system (for whatever reason) and the only way to change that is to make the cooling system work better. Thermostat doesn't do that.

There is no way that you could have the wrong waterpump is there? Only reason I ask is that I know on some GM applications different water pumps were available (reverse rotation) and they will make the motor run hot, but surprisingly to me, sometimes not hot enough to boil over.

If you can afford it, run the least amount of antifreeze the bottle shows as a sufficient mixture. I'm not sure how much better it cools when talking say 30/70 mix vs 50/50, but water is a better coolant than antifreeze, so it certainly wouldn't hurt your problem to reduce the mixture next time you were in there. Unless of course you HAVE to have the freezing protection the 50/50 mix provides. Just to prevent a follow-on post, note that the antifreeze manufacturers rate their "boilover protection" claims on testing using 15 PSI. VERY little (percentage wise) of their claim of boilover protection is because of the antifreeze. In a 15psi system the boiling point of straight water goes to approx 257 degrees. If you hit 257*, forget about the antifreeze, if you didn't catch the problem by then, it's far too late for the additional 10-15* a 50/50 mix will get you.

RBob

iTrader: (1)

The air dam makes a big difference in cooling. Not only when rolling down the road, as these cars are bottom feeders for cooling air. But at a standstill they prevent the hot fan air from going forward under the car and back through the radiator.

The other item that makes these cars run hot is debris. Being a bottom feeder they pick up stuff off the road like a vacuum cleaner. Then deposit it between the A/C condenser and the radiator.

Pull the top mounting plate off the radiator (right there on top, just a couple of bolts). Then look down between the rad and the condenser. After about 50 K miles they can easily be 1/3 of the way filled up.

After cleaning it out I placed a piece of round foam pipe insulation between the top of the condenser and the sheet metal. This blocked off the area for debris to get between the two.

RBob.

jac113

iTrader: (4)

thanks Rob and eager, you bring up good points. When I installed the new rad there were'nt any debris behind the condenser that I remember. When I get more time, i'm going to take the car to a car wash and wash out anything that might be stuck between fins.

eager, your comment on cooling is pretty accurate. A cooler therm will only make my car take longer to get to operating temp. I'll be looking into modifying it to turn on the fans sooner and by installing a cooler stat. I'll probably go back to a 180 and look at a variable switch that will turn on at about 195 and off at 185 and stay on for while when I shut off engine. This will only make the fan work more but not a bad trade off for a cooler running engine.

thanks