I feel like an "idiot" about this, but it's fitting...
September 5th, 2016, 12:44 PM
#1
Got wood? I do! (an '89)
Thread Starter
Join Date: Nov 2010
Location: Southeast Michigan
Posts: 310
I feel like an "idiot" about this, but it's fitting...
1989 Custom Cruiser.
307 cu. in. V-8.
Hyperactive "Idiot" lights.
So she sits most of the year--and has an all-new cooling system including radiator, hoses, fluid, etc., circa last season--but despite never activating the red "LOW COOLANT" light EVER, as in forever never, she does now despite having fresh coolant all around and a brand-new (not "rodded" or rehabbed or whatever) replacement for everything cooling-related.
Pop off the radiator cap and it's fresh, green and clean all the way to the line, and the overflow tank is at the right mark "cold" and "hot". I would roll the dice on it like the red "OIL/CHOKE" light that comes on at a stoplight or the amber "SERVICE ENGINE SOON" one that pops up for a few seconds at a completely random time and for no apparent reason it all (save for 176k miles without EVER touching the motor), but without knowing why, I gotta ask.
Between her nap from Dec. to, well, this week--I had just started her weekly and kept her fluids checked. But yesterday's "full" workout started with a lit "LOW COOLANT" red lamp that steadily (and silently) glowed for no obvious reason as her cooling system was overhauled last summer.
My massive B-Body factory manual lists--as you'd expect--low coolant as the culprit, but as I've said, that seems unlikely as she's properly filled, doesn't leak and is (mostly) new there.
1989 wasn't that long ago, so why are all the controls so cryptic? Counting the flashes to decode the pre-OBD II system is one thing. Trying to decode the reasoning behind an idiot light coming on when all the "necessary" conditions are met is another...
307 cu. in. V-8.
Hyperactive "Idiot" lights.
So she sits most of the year--and has an all-new cooling system including radiator, hoses, fluid, etc., circa last season--but despite never activating the red "LOW COOLANT" light EVER, as in forever never, she does now despite having fresh coolant all around and a brand-new (not "rodded" or rehabbed or whatever) replacement for everything cooling-related.
Pop off the radiator cap and it's fresh, green and clean all the way to the line, and the overflow tank is at the right mark "cold" and "hot". I would roll the dice on it like the red "OIL/CHOKE" light that comes on at a stoplight or the amber "SERVICE ENGINE SOON" one that pops up for a few seconds at a completely random time and for no apparent reason it all (save for 176k miles without EVER touching the motor), but without knowing why, I gotta ask.
Between her nap from Dec. to, well, this week--I had just started her weekly and kept her fluids checked. But yesterday's "full" workout started with a lit "LOW COOLANT" red lamp that steadily (and silently) glowed for no obvious reason as her cooling system was overhauled last summer.
My massive B-Body factory manual lists--as you'd expect--low coolant as the culprit, but as I've said, that seems unlikely as she's properly filled, doesn't leak and is (mostly) new there.
1989 wasn't that long ago, so why are all the controls so cryptic? Counting the flashes to decode the pre-OBD II system is one thing. Trying to decode the reasoning behind an idiot light coming on when all the "necessary" conditions are met is another...
Last edited by auto_editor; September 5th, 2016 at 12:57 PM.
September 5th, 2016, 02:22 PM
#3
72 Olds CS
Join Date: Jun 2011
Posts: 6,657
There is probably a low coolant sensor maybe located on the over tank that is unplugged or malfunctioning
I just looked on rock auto, standard fls38 is the low coolant sensor if yours is not unplugged it's likely its nfg, $18 on rockauto, prolly $30 at your local store
I just looked on rock auto, standard fls38 is the low coolant sensor if yours is not unplugged it's likely its nfg, $18 on rockauto, prolly $30 at your local store
Last edited by RetroRanger; September 5th, 2016 at 02:25 PM.
September 6th, 2016, 06:07 AM
#5
Registered User
Join Date: Jul 2013
Location: Mo-Ray-Al, K-Bec.
Posts: 1,815
As a rule on older vehicles, when a problem can have either an actual source, or be caused by a failed sensor .. I always wager on the sensor. Seems like they keep putting more and more sensors into cars to detect failures, and more and more the only failure they detect is their own.
September 6th, 2016, 01:55 PM
#6
Administrator
Join Date: Oct 2009
Location: Poteau, Ok
Posts: 40,561
As a rule on older vehicles, when a problem can have either an actual source, or be caused by a failed sensor .. I always wager on the sensor. Seems like they keep putting more and more sensors into cars to detect failures, and more and more the only failure they detect is their own.
September 7th, 2016, 08:00 AM
#7
Old(s) Fart
Join Date: Mar 2007
Location: Northern VA
Posts: 47,311
You all realize that this system is completely explained in the CSM, right? The coolant level sensor is simply an on/off switch. It is normally open when dry and closes to ground the sensor wire when it is wet with coolant. The sensor plugs into the chime module, which in turn triggers the light. That circuit is simply an inverting circuit - when the sensor is grounded it opens the wire to the light and when the sensor is open, it grounds the wire to the light.
Here's the simple test. With the key on, pull the wire off the sensor. The light should be on. Now ground this wire. The light should be off. If this works, replace the sensor. If not, there's either an open in the sensor wire or the chime module is bad.
FYI, this sensor requires a ground path on the threads. If the original brass radiator has been replaced with one having plastic tanks, guess what?...
Here's the simple test. With the key on, pull the wire off the sensor. The light should be on. Now ground this wire. The light should be off. If this works, replace the sensor. If not, there's either an open in the sensor wire or the chime module is bad.
FYI, this sensor requires a ground path on the threads. If the original brass radiator has been replaced with one having plastic tanks, guess what?...
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