UAOS and coolant light trouble shoot help please

I have a 99 Cab and I recently had the UAOS installed. If I missed this in the thread I apologize. It is my understanding that the UAOS is tied into the coolant light on the dash. The tech filled the coolant and it was purged so there are no air pockets. However, when I drive the car once the temperature is at about 190 the light starts to blink indicating low coolant, but it is not low and there is no oil in the UAOS. Has anyone else run into this issue? Tips, suggestions, resolution?

Contact skip directly. There was an update on the sensor and logic. Its a pretty easy to replace it u did get an older set up.

Classic air pocket problem. Flip the wire bail on the black pressure vent diaphragm to virticle position, overfill coolant tank by 3/8 inch and drive through a few heat cycles while keeping an eye on the level.. ......the air pocket in the top of the front radiators will cause the coolant level to drop under rpm and temperature...then return to look normal

We have tried that but it is still persisting.

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I have found that the original harness/ logic works just as well as updated version IF the coolant level doesn't drop under rpm/pressure/slosh....

Is your cab a manual or a tip? A tip has some addl coolant lines.

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You " overfilled" the coolant?? By how much???

It’s a manual. I will have to double check the amount it was over filled. I notice that if I turn the car off and turn it back on it goes away.

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Yea, it resets after you turn it off, then back on. The Instrument Cluster has some silly logic to it IMHO... Just overfill the coolant tank by 3/8-1/2" then drive with the wire bail vertical for a few days. I have found that this cures the issue, and the updated harness/logic was unnecessary, the problem was never in the UAOS to begin with but the silly logic in the Instrument Cluster and intermittent coolant sensor activation. But the UAOS has a 2 year Unlimited Mileage Warranty plus a "Lifetime Warranty on the AOS".. and good product support...!!

I think the design is brilliant and I am glad and future owners will be happy to have it. I am glad I have it in and will do it again. I will double check on the amount of over fill.

I had this exact issue - 2003 C2 six speed. When I installed the UAOS, first gen sensor, without the coolant bypass, I lost a very small amount of coolant doing the install, from the AOS coolant hoses. Coolant level looked normal, but every drive, right at the 185-190 temp mark, the light would slow flash. Discussed with Skip, filled the reservoir overfull, kept the bail up, problem went away. Back to normal.. -Tom

I appreciate the feedback.

Developed similar problem recently. 1999 C2. UAOS. Track drain back. Slow flashing coolant light. Coolant level fine. Doesn't occur at cold start, but starts flashing while warming up. No overheating. Don't think it's the UAOS as have the track drain back installed. As suggested above, overfilled a little, flipped up vent on coolant reservoir for a week. Little bit of coolant overflow, but no change in slow flashing light. Unplugged coolant level sensor - flashing stopped. Replaced sensor. Unfortunately, no change in slow flashing light. Interestingly - if car gets up to temp. Turn off and back on - no flashing light. Is there a way to check the coolant level sensor? Maybe I got a bad one out of the box. How about the coolant tank "float"? Engine temp sensor is in place.

Do you have the UAOS plugged into the coolant sensor in the coolant tank? If yes, disconnect it, plug the factory connector into the coolant sensor and then drive the car for a while to see if the light comes on again. If it does, the issue is with something in your coolant system. If not, the issue is the sensor screwed into the UAOS tank. I had a similar issue with my 02 996, except my low coolant light used to come on almost immediately, then shut off for a while and then light up again. Skip worked with me to isolate the issue. It turned out the sensor that screws into the UAOS tank was too sensitive for my car. Even vapors were setting off the coolant light. It took a couple of tries with different sensors and the problem was resolved. Test first then reach out to Skip.

Thanks Joel - will give that a try and report back.

The "slow blink" function is sensitive and has three separate circuits that can cause activation.... 1. the low coolant circuit ( has a float with a magnet attached and a magnetic switch/sensor) 2. the engine compartment temp sensor and deck lid fan ( if the temp sensor has fell out of the intake manifold and is laying on the engine or the deck lid fan is inop can cause the slow blink) 3. the UAOS warning circuit ...( warns of excess accumulation in the Accumulator ) NOTE : the Microprocessor Controlled Infra-red Sensor is very sensitive. If unplugging the low coolant circuit stops the blinking then that eliminates the other two circuits from consideration... The 99 year models had issues with the tank it's self causing "false warnings" and a TSB was issued and the tank was revised, so if it is the original 99 tank then that can be an issue.. As the temp comes up to operating temps and the pressure builds in the cooling system the rubber hoses can expand and cause the coolant level to drop slightly. If the float is not floating well ( heavy) that can cause the slow blink ... The low coolant switch/sensor can be bench tested with a DVOM and a magnet for switching/sensing ...Just check for continuity then place a magnet in close proximity... Since there can be multiple causes on three separate circuits of the slow blink function, you must be very careful and deliberate in the diagnosis process...

I had the same problem with coolant light coming on with the UAOS kit. Skip sent me new harness with sensor and it didn’t solve the problem. I reconnected factory harness to sensor and had no problem with coolant light coming on. Since I have the drain back modification I have eliminated the sensor for the reservoir and just use factory harness to coolant level sensor, coolant light works as it should. Mine is also MY 1999 and I have only heard of this problem on 99’s.

I have two versions of the UAOS Microprocessor Controlled Infra-red Sensors both are made by SST Sensing in the UK... The Stainless Steel /glass tip Sensor is used in the Elite version..( heavy-duty, but is not very sensitive ) The Polysulfone Sensor used in the AL versions..... ( medium-duty ( which is plenty), and is very sensitive) .. I have not had ANY issues with the Stainless Steel/Glass tip Sensors, and the issues with the Polysulfone Sensors seems to be only in certain climates/humidity and only on certain cars...I think the polysulfone Sensor is just "too sensitive" for certain cars/climates... SST Sensing is working with me to customize the Polysulfone sensors for us that are "less sensitive" .. They are sending me some for testing that has a coating on the tip to make it less sensitive to moisture/humidity for our cars.... @Jnelso I have been asked many times if the Sensor/warning circuit can be eliminated when the Track Drain is used....and I know that the possibility is very unlikely that the Accumulator will be overwhelmed with such a large drain on it. But there is still the slight possibility, and the engines are getting bigger and bigger for our cars.. So I recommend that the Sensor/Warning still be used even with the Track Drain... So in keeping with customer support I will send you one of the "new coated tip Sensors" when I get them and you can re-apply the Sensor/Warning circuit... Also like I just mentioned many of the "slow blink" problems have been traced to actual issues in the low coolant circuit and also the engine compartment temp circuit.. I had one issue that "only started after UAOS install" but it turned out to be only activating when sitting in drive-through's at the bank or fast food places, and was due to the engine compartment temp sensor had fell down on top of the engine ...so proper diagnosis is paramount..

Skip is awesome to work with. Talked with the tech who installed mine and got it sorted.

I have had the coolant light come on after warming up on some rides. Sometimes the blinking goes away while driving. Other times I shut the car off and the light does not come back on when I start again. I know my coolant is full. I will have to troubleshoot and see what the issue is. BTW I have the AL version without the drain.

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Thanks man, I've been in "automotive service" all my life life since 1974, it's all I know and I do it the way I would want/expect to be treated...

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The very first thing to do is "overfill" the coolant tank by 3/8" to 1/2" and lift the wire bail on the black "burp valve" on the coolant tank and drive a few warm-up cycles while watching the coolant level before starts.... This is the most common cause of the slow blink with or without UAOS and cures 90% of the cases with UAOS..

By overfill, do you mean to fill above the Max line.

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Yes

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As DeJeeper says,,,,yes .. The air space above the "max fill" line is intended to be room for expansion of the liquid coolant volume after it has raised in temperature ( compressing the air in the space ) ...But in real life on a 20 year old car what actually happens more often than not is the rubber hoses expand during pressure and causes the fluid level to actually drop instead of rise,,, you get a little compression of the air space along with and a little expansion of all the 22 hoses .... Couple this with ANY air pocket and you will sure nuff get the slow blinking...

Bumping an old thread� I had my local Indy install the UAOS on my 99 996 and sure enough first 20 minutes or so I had the slow blink� found this thread and even though they topped up coolant the reservoir was nearly dry! The car was running cool / normal but I did not need to pull up on release valve on tank, just needed to add more coolant and problem solved. I will go out for a few more drives and keep an eye on the level but I�m so glad to have the UAOS with track drain back package to protect my 3.8 stroker! First time my shop had ever installed one and they were really impressed though they took more than the 4 quoted hours� I am glad they did it and I needed a few other things addressed while the intake was off.

Glad they were impressed ,,the word is slowly getting out there !!!

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✅😎👍🏻 I wanted to follow up in case any 99 996 owner install the UAOS. I have put about 300 miles on the car since topping up and going just over the max mark on the coolant reservoir and everything is back to normal. I will post some follow up pics soon but it felt good to eliminate some old lines and now have the ability to change the AOS diaphragm in minutes.