Fans not running - radiator/GM

RnR

Joined
Dec 16, 2005
Messages
563
Location
Michigan, Thumb's Up!
As of late I've detected that my '99 Grand Prix's supplemental radiator cooling fans are not running at high system temps. Might there be a common failure mechanism that I should check first in troubleshooting this symptom? Thank you!
 
Joined
Mar 24, 2007
Messages
10,008
Location
Upstate NY
Checked the high-speed fan relay yet? Also, are you going by the dash gauge that is nothing more than a glorified dummy light, or the actual water temperature? The dash gauge's "normal" varies a lot. Could be it cooled down and your fans don't need to come on as much.
 
Joined
Oct 11, 2002
Messages
22,187
Location
Colorado Springs
How high is the temp gauge going? The older GM gauges are pretty accurate actually; they aren't dummy gauges. Older GMs are programmed to run pretty hot. We've had several GMs with 3.8Ls, and the low speed fan setting goes on at about 220, while the high speed setting kicks in at about 230. Do they turn on when the A/C is on? If you idle the engine when it's up to temp, even in cool weather, they should turn on after a bit as the needle on the gauge gets well past 200.
 

RnR

Thread starter
Joined
Dec 16, 2005
Messages
563
Location
Michigan, Thumb's Up!
My glorified guesstimate is based on the dash guage... and the last test indicated about 230F with zero fan activity. (The gauge seems to settle pretty darn close to the thermostat's 195F trigger during normal highway driving if that helps provide any assurance that the guage is tracking properly.) Fan relay (where might that be?) has not been checked, nor whether the A/C has any impact - I don't use that as the Freon is long gone!
 
Joined
Jan 7, 2008
Messages
137
Location
TX
I have an older 3.8L series II, should be similar. First, I'd locate the relay for the fan(s). Usually can find in the back of the owner's manual. Mine is under the hood, passenger side. There should be a few like relays which makes swapping easy while troubleshooting, just make sure you know what they do. Your coolant temp sensor (in intake manifold) should send the voltage to activate the relay, and thereby activating the fan. If the voltage isn't there when hot - it's the coolant sensor, or corrosion on the sensor leads. If it is there and the relay doesn't activate - it's the relay. If it is passed to the fan - it's your fan. Can't remember if the coolant sensor throws a code or not.
 
Joined
Oct 11, 2002
Messages
22,187
Location
Colorado Springs
 Originally Posted By: RnR
My glorified guesstimate is based on the dash guage... and the last test indicated about 230F with zero fan activity. (The gauge seems to settle pretty darn close to the thermostat's 195F trigger during normal highway driving if that helps provide any assurance that the guage is tracking properly.)
That is exactly how our Series II runs, except the fans turn on low at about 215 degrees and the temp then settles back to 200. Runs at 200 when on the highway regardless of ambient temps. So there is for sure a problem with yours like a fan relay.
 
Joined
Sep 8, 2005
Messages
15,229
Location
Canada
I just recently had to replace the radiator fan motor on my 2002 Cavalier 2.2 OHV. Thought it was just the thermostat not opening to click it on, so replaced that, but engine still nearly overheated. Checked the relay, it seemed to be fine. Electric fan motor was burned right out.
 
Joined
Mar 24, 2007
Messages
10,008
Location
Upstate NY
Time for a multimeter! Also, there are lots of ways to get your fans to kick on sooner. The automatic, if sorta spendy, solution is to get a reprogrammed engine computer and a 180* F thermostat. The fans will kick in at 186* F then. I did this to my Buick LeSabre with the 3800 SII. Works like a charm! Highest coolant temperature I've seen since then is 195* F, climbing a very steep, long hill at low speeds with a fully-loaded car.
 

RnR

Thread starter
Joined
Dec 16, 2005
Messages
563
Location
Michigan, Thumb's Up!
My vehicle has (2) fans - neither of which are activating. So, I think that relay is the prime suspect if it is receiving an appropriate voltage from the coolant sensor. So, I'll first look at the wiring and see if there is anything obvious amiss - then start poking around for the relay. Thanks, gents!
 
Top