View Full Version : coolant fans

Harry Yarnell
03-15-06, 07:14 AM
At what temps do the two coolant fans come on? I got up to 222 the other day, and no fans. I shorted out the dk blue and dk green leads to the PCM, and the fans ran at high/low.

03-15-06, 03:38 PM
224-225 for me.

Rob Benham
03-15-06, 05:25 PM
As per my thread "94 SLS losing streak" I found out today that my fans do come on just a tad over the book figure 223-225 I think. You may have just missed it.

It then went to 255 and A/C compressor shut-down.

I have never let my engine get over 213 before, and having just fitted a new rad, I'm @#$% off!!

I'm interested in the way in which you caused your fans to come on by shorting the wires, could you give a description of just where you located the wires, and if you shorted them to ground / each other or whatever?

I know where the relays are.

It has been my intention for some time to be able to turn the fans on to low without the A./C running all the time. I'll do it now if I haven't wrecked the most beautifully smooth engine I have ever owned. Thanks


03-15-06, 05:29 PM
224 is what our old guru always said.

Harry Yarnell
03-15-06, 06:05 PM
The vehicle is a '97 Deville; I will assume others are similar (I've gotten in trouble before making assumptions... but I digress). There are three fan relays sitting on the bottom of the radiator rail, and the leads are accessible at this point. The fans run at two speeds; BOTH fans are placed in series for low speed, and both fans are placed in parallel for high speed. The PCM grounds the dark green lead for low speed, and grounds the dark blue for high speed.
I'm also thinking of tapping these two (or one) leads, and bring them into the cockpit for a manual switch.

Rob Benham
03-15-06, 06:11 PM
If i still have an engine, I'll do that mod. Thanks.

Harry Yarnell
03-15-06, 08:30 PM
BTW, these dark blue and green leads are about 20 ga. wire. They are the smaller wires in the bundle going to the relays.

03-15-06, 11:33 PM
No no no do NOT do that. Get yourself a remote switch so you don't have to drill your firewall. I've done it on 2 Cadillacs now (the remote switch and relay unit) and it's great. Never done it for fan, but it would work.

03-16-06, 10:51 AM
If the system is operating properly there is no need to override the fans. If not, overriding them is just a band aid and buying time til it gets worse and must be fixed. If you are overheating, find the problem now and fix it.

03-17-06, 12:22 AM
I agree. Some people will come up with idiotic rigs until they day they die though, it does no good telling them otherwise.

Harry Yarnell
03-17-06, 02:25 PM
OK, looks like 224-5 is the cut-in for the low speed; what's the temp for high speed, and does the A/C use high or low speed.?

BTW, checked that indeed the fans do kick in at an indicated 224

03-17-06, 07:46 PM
AC I believe steps up the speed. If fan off, AC starts it on low, if on low, AC moves it to high speed.

03-17-06, 09:22 PM
High speed is 230 degrees, give or take a degree.

Rob Benham
03-17-06, 10:35 PM
There was a discussion some time ago about keeping the temp within a narrow range. Bobinski I think it was, said let it do its thing. Another poster said why, if you can maintain the temps at a lower level would you let them go as hi as 230.

I did not contribute, but thought that I would keep my temps as stable as possible. I visualized the expansion cycles, in particular on the head as associated bolts, and joined the conservative band. Well, I owned an old car that was sweet, why not keep its parts as static as possible?

At traffic lights, I would turn the a/c on just for the fans...which on mine by the way, come on full with a/c.

There is a great deal of difference between a young enthusiast (of any age) and an old git that can't stay bent under the hood for more than a minute at a time. Any engineering I do now has to be fun, not a long slog.

The one thing that we try to do with aircraft engines, is keep their temps as stable as possible...piston or turbojet. It pays in the long term, even if there are a whole list of exceptions to the rule.

I like the idea of the remotee, good call, but I think that I have a couple of redundant wires anyway...and all of this is academic if my head gasket's bust!