: Cooling fans running

11-22-10, 02:58 PM
Ok - this one's complicated. Or I may be over-complicating it.

I swapped the "new" engine into the car. It's out of a Caprice. I accidentally broke the engine coolant temp sensor (ECT) on the Caprice engine (actually my brother did it...just sayin'). I swapped over the original ECT sensor from the Caddy. I also swapped over the engine coolant temperature SWITCH (for the idiot light).

Before the engine swap, I never saw the secondary fan run at all. I was starting to think maybe it was broken. According to the manual, the primary fan comes on at 225 degrees and the secondary fan comes on at 232 degrees.

With this "new" engine, BOTH fans run all the time once it's warmed up (this is important: they do not run when you first start it, only when it reaches operating temp). Complicating matters, I had the PCM reflashed to eliminate certain emissions related checks. The guy that reflashed it said that he put the cooling fan triggers at 198 and 205. I guess the first question is, can the engine run this cool with the stock thermostat? I'm imagining that it could since the stock thermostat appears to be 180 (at least according to NAPA - is this right?).

So, if we assume that the fans can bring the temp down below 195 (particularly at this chilly time of year), then why are both fans running? Bad thermostat in the new engine? I don't think it's running hot - it's not boiling over or anything.

Or...the PCM flash guy said that the PCM will go into a self-protect mode and run the fans constantly if it senses that both knock sensors aren't hooked up (they are) or if the MAF is unplugged (it isn't). I don't have any codes stored.

So what would you do? Swap the thermostat?

Is there any way to see what temperature the car is actually running at without taking it to the stealer?

Oh yeah. During my research, I found this little tidbit in the service manual. Note the diagrams and the labels (hint: location of primary and secondary fans). It's no wonder people go insane trying to do DIY repairs:

http://turbojimmy.4t.com/Fleetwood Cooling Fans - Section 6E.jpg

http://turbojimmy.4t.com/Fleetwood Cooling Fans - Section 8A.jpg


11-22-10, 04:11 PM
that's an interesting problem. I did read how to test a thermostat in my FSM. It said to put some coolant into a pan and put it over the stove. put your thermostat in there and also put a thermometer to see the temp. that way you can see when thermostat is opening etc...

Not sure if that helps you or not, but you can also check your coolant temp in the climate control thing.

11-22-10, 04:16 PM
Not sure if that helps you or not, but you can also check your coolant temp in the climate control thing.

This would help immensely. I almost spent $135 on a scanner today....just to see the coolant temp. I know the Devilles do it, but didn't know I could do it on the 'Wood. Is there a link somewhere with instructions (the search feature sucks).



11-22-10, 04:43 PM
198 and 205 seem a little low. I have a 195 thermostat and a coolant gauge that ranges between 210 and 225 during normal operation, so your engine is probably surpassing the 205 temperature mark, which is turning on both fans.

Think about it this way, the primary fan, which was set at 225, used to come on periodically, which means the engine reached that temperature periodically. If you changed nothing about the way the engine runs, except the parameters in the computer, then the engine is still going to periodically reach 225. Normal operating temperature for that engine is probably around 210, so I would say to have the ECM re-flashed to set the triggers around 215 and 222.

11-22-10, 04:50 PM
look in the RWD FAQ thread. It'll tell you, there's a video at the bottom of that post and I believe it shows it.

11-22-10, 04:55 PM
Okay - so maybe I am over-complicating it.

I was just outside adjusting the headlights (right one is pointed at the ground for some reason). Started it up cold. While searching for the appropriate Torx screwdriver, the fan came on. Yes, singular - "fan". The primary fan came on by itself. So both fans are not coming on simultaneously, so it's not a PCM protect mode event.

I guess it is getting warm. I didn't let it run long enough for the 2nd fan to come on but I assume it would have at some point. I think things point to the thermostat at this point?

Now I've read thing about bleeding or burping the coolant system. I did no such thing. The manual said that it takes 14 quarts. It took every bit of 16 quarts (4 gallons) due to the rear heating. While filling it, I removed the bleed screw from the thermostat housing neck, but that's it.

Further research required....

11-22-10, 06:25 PM
Wow. So I CAN see the coolant temp through the HVAC controls. Awesome.

Of course, I can't duplicate the behavior. Sitting in the driveway I could see the temp climb steadily to 180, saw the temps steady when the thermostat open, then I got bored and went in the house for a beer. Fan didn't come on.

Next time both fans come on I'll trigger the HVAC coolant temp readout thingy.

11-22-10, 07:31 PM
cool man. good luck tracking it down. keep us posted

11-22-10, 08:01 PM
So I got to my dad's house and both fans were running. Temp was 182. Something not right. I'm thinking it's the way the PCM is programmed. Once I get a good inspection sticker I'm going to swap it out for the stock PCM and see what happens.

11-23-10, 10:47 AM
So the plot thickens....

When I got into the car this morning it was 45 degrees outside. The car had been sitting all night. When I started it, I noticed the blower motor was running. Evidently the PCM thought the car was warm enough to provide heat (it wasn't). I checked the coolant temp and it said 100 degrees. Impossible. If the PCM doesn't think the coolant gets any colder than 100 degrees, this is going to start to affect the warm up cycle as the weather gets colder.

Yet when the car is fully warmed up, the 180-182 degrees that it shows seems to be accurate. And, the second fan is running at 180 degrees (still don't know when it turns on) despite the PCM tuner guy's assertions that the second fan doesn't come on until 205.

On the cold start this morning the primary fan was running, but I think it will come on if the A/C is running (it was).

I'm thinking it's something the PCM tuner did. If it were bad information from the coolant temp sensor, the second fan wouldn't running at 180 degrees. I ordered a new temp sensor anyway just because the $25 was burning a hole in my pocket.

Good news is that it passed emissions inspection today. I have the old, stock-programmed PCM here now. I'm going to let it cool down and pop it in. That should be the definitive test.

11-23-10, 11:40 AM
cool. I'm intrigued by this problem. Can't wait to hear the final verdict. :D

11-23-10, 12:05 PM
The blower motor will run, along with the AC, at start up if its on defrost. Any other setting, it waits to warm up before coming on.

11-23-10, 12:14 PM
The blower motor will run, along with the AC, at start up if its on defrost. Any other setting, it waits to warm up before coming on.

Thanks. It was on AUTO, set at 72 degrees.

11-23-10, 02:32 PM
Well, the problem is my "tuned" PCM. When I put the stock PCM back in the fans don't run at all. This time of year, with around-town driving, temps stay at around 180 degrees so the fans don't need to run. Not sure what the guy did, but both fans are coming on way too soon. The car runs great otherwise, but the PCM will need reflashed to correct this fan thing.