Question: Low coolant light comes on but levels look ok

[k2bob]

Hey Guys,

Thanks for all of the help with the warm start problem and fan issues. My mechanic was hesitant about some of your thoughts and suggestions but it turns out that you both were right. Anyway, I spent a lot of $$$$$$$$$$$$ to revive this awesome car so now some of the
-I hope-little things I hope to do myself.

Yesterday the low coolant light came on for the first time. So I stopped and checked the fluids in the radiator and the reservior. Both were good and the coolant looked like new.

First of all could this be a contaminated sensor or is it telling me that there is not enough coolant in the engine prior to thermostat opening? It did the same thing today and stayed on for a 50 mile trip. Coolant temps stayed at 175-177 on the highway and got up to 186 in town then back down to 177 on the highway. Return trip, no light.What do you think? I'm thinking it is a bad sensor.

I plan to open the radiator cap tomorrw morning and let it idle until I see a drop in the radiator level. If no drop occurs after 195 degrees I assume the engine is filled to capacity. If it drops, I'll add some more coolant until the level in the radiator stabilizes to insure there is now low coolant.

Is there anything else I need to look for?

 

[Schrade]

Air in the system.

A few drive cycles will bring the air up top. I don't think I've ever used the air bleed outlet on a car...

Mechanic was hesitant huh? Send him an email with a link here, because I accept his diagnostic 'challenge'. And I never got a nickel for gettin' a wrench-on either nope

 

[G Winter]

It could be air or the sensor which is basicly a grounding device. I doesn't take much crud on it to cause a problem.
It could even be the connection on the probe.

Glenn

 

[k2bob]

Yeah the mechanic was a little hesitant because he had other codes come up and wanted to eliminate the little things first because the car sat for so long and was not properly maintained. Our "ah ha" moment came when we were able to do the injector ohm check when the engine was warm. He became a fast believer in the articles and comments from CAC to start with your suggestions first.

Anyway, the low coolant light came on again this morning. So I watched the coolant rise up in the radiator starting at about 150 degrees. It kept rising so it overflowed slightly. I put the cap back on and the next time I started it up the light was off. I am pretty sure there is no thermostat in place, otherwise I should see a brief decline in coolant temp when the thermostat opens for the first time. Right? But that does not happen. The temp keeps rising at a very steady pace and evens out at about 177 when on the higway with 70 degree outside air temp.

Thanks Glenn, now I just have to figure out where the ^%#@&() probe is located so I can check it out. Remember, I'm still kind of new to this Vette thing but am learning fast thanks to guys like you.

 

[Schrade]

Some fluid sensors use the fluid as a conductant, and measure the conductivity of the fluid itself. I don't know if vette coolant sensor is like this or not.

BUT, if it IS, then when the coolant is off of the 2 wire electrodes of the sensor, there's no conduction - open circuit - and the DIC says low coolant. IF this is the way it works, it is probably calibrated for perfect coolant mix - electrochemically speaking. Not only could low coolant be the problem, but possible a bad mix could be the problem; but I'm not certain the vette coolant is like this.

Some other vehicles' fluid sensors ARE like this...

 

[k2bob]

Thanks, I forgot the conductivity part. Is there an electolite test I can do or should I just replace the coolant? The coolant looks and smells brand new. If the conductivity is too low does it affect anything else? In the mean time I'll keep researching and learning.

 

[Schrade]

I don't know for a fact that what I said is actually how vette coolant level sensor works. Many newer vehicles are like that. Someone else here will confirm or deny.

Check FSM too Vol I sec 6B

 

[G Winter]

Just checked my electrical supplement . The low coolant is shown as a switch closed with low coolant not sure how it closes.
location is shown as , RH rear of engin compartment at bottom of coolant reservoir. This is on a 90 L98.

Could just be two probes in the reservoir with one to ground.

hope this helps.

Glenn

 

[Schrade]

Just checked my electrical supplement . The low coolant is shown as a switch closed with low coolant not sure how it closes.
location is shown as , RH rear of engin compartment at bottom of coolant reservoir. This is on a 90 L98.

Could just be two probes in the reservoir with one to ground.

hope this helps.

Glenn

Did the supplement give a range of spec values for the sensor, or just an 'Open/Close' switch function???

If the former, it is conductance measurement. If the latter, it is also conductance, but only as an 'On/Off' reading, as in 'immersed (in coolant), or NOT immersed.

Where's that HibH guy - I bet he would know...


Edit:
DUH. Stop thinkin' so much uh huh. 'Tard. Pffft.

Yesterday the low coolant light came on

What does the sign say? It doesn't say 'Check' Coolant; it says 'LOW' Coolant.
No wonder I never got a check for wrenchin'.
Quittin' time. Ugh...

 

[G Winter]

The drawing just says close with low coolant so there has to be another part . I will look in the service manual this afternoon after work for more info. Headed out to work now.

Glenn

 

[k2bob]

Hey guys,

Just a follow up to let you know what I found.

Mine was a loose wire connection on the sensor which is located on the passenger side of the radiator about 1/4 down from the top on my 89. It was good to see all the theory and science used to help sort out the possible solutions. Fortunately mine was easy.

 

[Randys88Vette]

88 had same problem

Hey there...my 88 does the same thing STILL, on some days. I have found that when this happens, it is letting me know the reservoir is empty. I replaced the radiator and the sensor, which is located about 2" down from the filler neck, about 2 years ago and the system is doing fine. But every once in awhile, during a hard run on the highway or horsing around on the street, i lose some coolant somehow. Havent figured that out yet, but since the sensor is so clsoe to the top of the filler neck, whenever the coolant level drops below that sensor, the light comes on. If the reservoir is in band (between hot and cold level markings on cap/stick), then it will fill the rad back up when the level starts to drop by suction. Same for when it gets overly hot and it flows back into the reservoir. Helps to protect your system from overpressure and overheating!

It doesnt take much for the level to drop to set that sensor off.

 

[vetteoz]

The drawing just says close with low coolant so there has to be another part .

Sensor is just a copper terminal that goes to ground through the water.When exposed to air it goes open circuit and the light comes on.
Relying on the heat/ cool oveflow bottle method may not get air completely out of system.Only sure way is to burp.

Warm engine to get thermostat open, remove radiator cap and give moderate revs.
The level in the radiator will usually drop.While holding revs pour in as much water as you can and put cap back on .

 

[G Winter]

Sensor is just a copper terminal that goes to ground through the water.When exposed to air it goes open circuit and the light comes on.
Relying on the heat/ cool oveflow bottle method may not get air completely out of system.Only sure way is to burp.

Warm engine to get thermostat open, remove radiator cap and give moderate revs.
The level in the radiator will usually drop.While holding revs pour in as much water as you can and put cap back on .

It says " closed with low coolant" The copper terminal opens the ground with low coolant.

Glenn

 

[ken mohr]

I had the same problem. Wound up taking it to the shop for a pressure test. Found that the cap wasn't sealing. They tried 14 caps and couldn't get it to seal. The short of it was a change of radiator and end of problem. My advise get a pressure check done looking for a leak. Have it done on the car. Mine was fine when submerged in tank.

 

[vetteoz]

It says " closed with low coolant" The copper terminal opens the ground with low coolant.

There is a "low coolant module" that works on the resistance it sees from the sensor to operate the coolant light.
<10K ohms ; level OK
>50K ohm ;low coolant

 

[tonybabb]

Hey Guys,


Yesterday the low coolant light came on for the first time. So I stopped and checked the fluids in the radiator and the reservior. Both were good and the coolant looked like new.

First of all could this be a contaminated sensor or is it telling me that there is not enough coolant in the engine prior to thermostat opening? It did the same thing today and stayed on for a 50 mile trip. Coolant temps stayed at 175-177 on the highway and got up to 186 in town then back down to 177 on the highway. Return trip, no light.What do you think? I'm thinking it is a bad sensor. QUOTE]

I bought my 89 coupe new and remember there was a little slip of paper that came with it saying that occasionally the low coolant light would come on and not to worry, just monitor the temp and the light would go out. So, seems like it's a design/ manufacturing problem that GM never fixed...sigh. My low coolant light comes on occasionally, mostly after I've added/ replaced coolant, this happens for a few days/ weeks then it stops happening. That said your temps sound too low to me, it should have a 195f thermostat and the engine will run at 195 or thereabouts. Certainly mine runs at around 190 - 195 on a nice 70f day.

 

[CorvetteArchives]

Hey Guys,


I bought my 89 coupe new and remember there was a little slip of paper that came with it saying that occasionally the low coolant light would come on and not to worry, just monitor the temp and the light would go out. So, seems like it's a design/ manufacturing problem that GM never fixed...sigh.

Apparently GM still hadn't solved the problem by 2000 which was the LAST time anyone in our family bought a GM car! For no logical reason it did that on my father in laws 97 cavalier, our 98 sunfire and another 2000 cavalier. GM must have sent all the faulty vette sensors to the J body cars!
By then English had been replaced and it looked like a glyph of "sailboat" that we'd hear my sister in law constantly complaining about. From what I recall it actually was recalled and then still didnt work right!:W
And people wonder why GM whent bankrupt?:bash

 

[tonybabb]

Apparently GM still hadn't solved the problem by 2000 which was the LAST time anyone in our family bought a GM car! For no logical reason it did that on my father in laws 97 cavalier, our 98 sunfire and another 2000 cavalier. GM must have sent all the faulty vette sensors to the J body cars! ?:bash

I just came across the slip of paper - it was definitely from GM, not the dealer. Basically it said the low coolant light might come on especially after changing coolant. It went on to say that you should drive it through five (5) cycles of driving it and then letting it cool down completely - ie overnight. If the light was still on then take it to the dealer. I just put new coolant in mine - along with new cylinder head gaskets, water pump, valve job etc. Sure enough the low coolant light came on the first two days I drove it and hasn't come on since.