1990 C4 Automatic, Base Model

For about three months now, I get the Low Coolant light on the climate control screen. When I check the coolant, the level has gotten low. The coolant is going somewhere. I did a pressure test, and it stayed at 17PSI for about 25 minutes.

I checked the plugs to see if any were discolored or wet. All plugs looked the same, light tan, dry, and not fouled. I ran my finger around the bottom of the tail pipes and the tail pipes are clean with a small amount of soot in them, but dry. I put a white box under the car at night to see if any coolant (or oil) makes it's way down to the white box. None detected.

Has anyone had this problem, and if so, what was your fix? I top off the coolant every 50 miles or so.

 

Well, If it is not being burned in the engine it is leaking somewhere. I had this exact same thing happen to me and it was a seeping leak in the radiator that never dripped. I would start by removing the radiator and taking to a shop to be pressure tested under water. How much are you adding every 50 miles? Dan

 

Today, I did more testing. For instance, I filled the system, and I pressurized it with my kit. I pumped it up to 19 PSI, and I left it sit and monitored it for just over one hour. Interestingly, the pressure did not drop at all.

I looked around to see for evidence of leaks or residue from leaks. I saw one unusual thing. There was some residue on the coolant fill container, the black container with the radiator cap.

I made the presumption that the radiator cap was letting water pass by and leaking out. So, I replaced the radiator cap, and I will check the fill each day to see if the coolant is still there or still leaking out somewhere. After letting the pressure test extend for over one hour, I was convinced that it is not a head gasket or a leak in the radiator or hoses.

 

I wonder if having the system at operating temperature would encourage the leak.

 

I do not know if having the system operating at temperature would encourage a leak. I will monitor it having a new radiator cap, and if the system normalizes, I will presume a fix, if the coolant decreases in volume, I will look at the next possibility.

 

Have you pulled the oil dipstick? I would do that and make sure you don't have what looks like chocolate milk for oil! You could get some UV dye for the coolant....add that to the radiator and run it up to regular operating temperature, to get it circulated through the system and hot. After cool down, pressurize the cooling system again with your tester, 19 psi is more than plenty, a pound or 2 over the cap rating is enough. Let it sit overnight. To see the UV dye, you'll need some yellow safety glasses and a black light, you can find yellow safety glasses at home improvement store/Walmart, etc...Hobby Lobby has a nice little black light led flashlight in the kids science projects section (by the toys and models) for $3.99 and they work awesome ($2 glasses and $4 flashlight, instead of a "UV dye detection kit" at the parts store for $40+) After sitting overnight, crawl all around the car above and below, looking for the florescent dye. What is the pressure, after sitting overnight? Also, check the carpet on the floor boards, especially the passenger side....wet? Lastly, you were asked previously, how much coolant are you adding every 50 miles? Good luck, it's going somewhere, and it is possible for a head crack to expand/open when hot and shrink/close when cold, but this doesn't last long as the crack usually grows with heat cycles! Could be a soft/freeze plug (sneaky ones on the back of the block)! You'll find it👍

 

1990 C4 Coolant
I changed the oil a few days ago, it is was not dirty. The old oil had about 2000 miles on it, maybe less. It did not show signs of contamination. I purchased the UV dye for the oil and for the coolant. I replaced the radiator cap and will monitor to see if it makes a difference.

I will pressurize the system and leave it over night. I have the UV glasses and light. I will check for leaks or UV residue the next day. I have been checking to carpet for moisture from the heater coil leaking. When I add coolant, it is after the light in the temperature cluster comes on. I usually add about one gallon of water when I do add. Yesterday, Monday, the light came on, and I added one gallon after it cooled down.

Now, I drove the car a good distance on Monday after adding one gallon of water and installing the new radiator cap. I tried to open the radiator cap after I returned home, and the container was full. I will drive and see if the light comes on, and see how much water it takes, if it requires any.

 

OMG!!! A gallon every 50 miles? I can't believe this is not easier to find. Dan EDIT: was the white plastic overflow tank overflowing?

 

The white overflow tank was not overflowing, but, it was full when I opened it. I do not think that my system is pulling that water out. I think, now, that there is where my water is going.

Again, I do not think that the system is pulling that water out of the overflow bottle. What is causing water to be there in the first place, and what is keeping it from returning into the cooling system. It was full to the top.

 

When the system expands it is very easy for water to bypass the radiator cap and flow to the overflow tank. When it is time for the system to suck back the fluid when it cools down this is harder. The system has to suck by vacuum so any small leak will break this vacuum. Check all the lines from the pressure tank to the overflow. A small leak will not stop the coolant from flowing from the pressure tank to the overflow but WILL stop it from being sucked back. Dan

 

Okay, Dan,

I will check the soft line from the overflow to the pressure tank. I have a new radiator cap and will see if that is the solution.

I purchased dye for the radiator and for the oil. I will put it in the radiator first and see, with UV testing equipment, if I find dye coming out somewhere, including checking a quart of so of oil, again, checking for dye in the oil, or anywhere else on the engine or hoses..

 

Update,

I cleaned the engine well, top and bottom. I put some UV dye in the coolant and drove the car a few times. The oil is fresh from being changed a couple of weeks ago. I used my UV glasses and blue flash light to check around the engine, under the engine, and I removed a few tablespoons of oil. I checked the oil for dye. No dye was found in the engine oil. I measured my refill and put in about a quart when I see the coolant light come on.

No dye was fond anywhere outside of the radiator. Any idea of what my fix is?

 

Have you tried putting coolant into the reservoir and not the radiator

 

Try checking your passenger side footwell.

 

BET VETTE, I will try putting coolant in the reservoir. It is full of coolant right now. I am waiting for the system to withdraw it.

CA-Legal-Vette I have been feeling for wet carpet since I learned that this situation existed. the cabin, the passenger side in particular, the floor carpet, the foot area or firewall is not wet. it is bone dry, and there is no smell that suggest that water/coolant is leaking inside the cabin.

 

I will repeat myself. If the radiator will not suck back coolant as it cools down you have a vacuum leak in the line to the reservoir or a bad radiator cap. Dan

 

Thank you, Whaleman, please do not let this frustrate you. It's not that important

The radiator cap is new, just purchased it within the past week. I will go back in to see if there is a vacuum leak on the reservoir lines. I did not find any issue when I checked them, about a month ago.

 

Also check for a small crack in the pressure tank where the cap installs. Maybe get a cheap hose and jumper from the pressure tank to the reservoir. maybe a crack in the reservoir where the tube connects. Something is breaking the vacuum. Dan

 

This was the problem I had in my '90 when I couldn't figure out where I was losing coolant. I installed a replacement tank from Rock Auto and haven't had a problem since.

Reason it took me so long to figure out where the problem was is because you couldn't see anything actually leaking. I dunno if it was just vaporizing as it leaked or what. Probably was...

 

Which tank did you have to replace Natty? Dan