This summer I bought an 87 C4, 21K miles. I had a bunch of work done by a corvette restoration shop. Some of the engine work included removing and resealing the intake as well as new valve guide seals. New (reman) smog pump, new water pump and thermostat. They also replaced a heater hose. The shop told me that the coolant system was fully tested, had no air in it etc. I have only put probably a few hundred miles on the car since the work but all has been ok.

I was going to get it ready for winter storage and idled it for a bit before adding seafoam to the gas tank.

I noticed that the exhaust was still putting out some steam even though it had been idling for 1/2 hour and was up to temp but I figured it might be because it is 46F outside. Not a lot, just some steam still floating up from the exhaust tips. I need to drive it some to mix the seafoam in the tank so I was planning on doing that in the next day or so and figured it would go away after driving it enough to really heat up the exhaust.

I randomly took a peek at the coolant overflow tank while the engine was cold, about 3-4 hours later. The plastic one up by the front passenger wheel. There is a very small amount of coolant in there. Well below registering on the stick.

I never actually looked at it when I got it back from the repairs but I assume it was filled to the correct level after the coolant system work.

I am going to call them when they open but I wanted to get other opinions. Is this something to be very concerned about? Obviously it needs to be topped off, I will need to run and get some but, where did it go?

The very little coolant in the overflow tank looks a bit dirty, but the oil on the dip stick looks like good fresh oil to the correct level and the correct color.

 

That coolant overflow tank up front catches excess coolant from the other black resivoir when your coolant comes up to temp and expands. It also allows some coolant to be siphoned back into the radiator as the car cools off and the coolant contracts. We're talking about a very small amount moving back and forth normally..... but after the system has been opened, flushed, new coolant added etc... I think what you're describing is pretty normal. I think it's pretty near impossible to get all of the air out of the system 100% without driving a bit and topping off. So what happens is any air in the system collects at the high point, in that black coolant tank, and then when the engine gets hot and the coolant expands, only air is pushed to the overflow tank up front. However when the car cools down again after your drive, and the coolant contracts, it still pulls a small amount from the overflow tank up front, and probably more so to replace any amount of air that made its way to the black tank at the high point. I believe it's likely this is what's caused your overflow tank to run low, and nothing to worry about.

When I had my water pump replaced and system flushed earlier this year I was advised to top off the upper black tank after driving a bit. REMEMBER, ONLY OPEN THIS TANK WHEN THE CAR IS COLD! My car took about another 1/2 quart of coolant to top off and hasn't lost any in either tank since. The black one should always be full. Assuming you don't have a water leak anywhere, I think it's likely this is what's caused your coolant level to go down in the overflow tank. Just my 2 cents from my recent experience.

 

I wouldn't get stressed about it just yet. You're probably okay. If coolant is getting into the combustion space, you can usually smell it in the exhaust. Top off both reservoirs, and monitor the levels after a few heat cycles. If it's troubling you too much, You might want to have the system pressure tested for leaks.

Live well,

SJW

 

Same here. I also continued to hit the bleed screw after the next several drives just to make sure all the air was worked out.
The steam could be concerning assuming it isn't ambient temperature related. I would confirm all your levels and monitor them before you store it. Definitely don;t want coolant leaking in the engine all winter.

 

I don't see a cause for concern here. At the age, the bottom of the overflow tank will probably have a lot of crud inside. Its a snap to take it out and wash it clean.

Just fill the radiator and the reservoir to the proper levels. Drive it once and you'll see that the reservoir level will be higher when you shut it down compared to starting it again the next morning. That is normal operation.

Wisps of steam from the exhaust when its cold is normal. You'll also see water dripping out the tips if it had sat outside or exposed to real cold overnight.

 

Thanks for the advice.

I checked the radiator coolant level by removing the radiator cap (the engine was cold) and it is up to the top. I dropped it off at the restore shop. They are going to test it for me. Hopefully it was just some air that needed to work it's way out but I figured it's best to just make sure now before I put it away for the winter.

I will update when I hear back.

 

I don't think that it is normal for the expansion tank to be vitually empty. To the point that it doesn't even touch the dip stick.

Hopefully it was just some air that needed to come out, but if the tank was properly filled after the work was complete (I assume it was), that coolant went somewhere. If it's a normal thing that is a result of the work preformed, awesome. I will make sure it is topped up, put the car away for the winter and problem solved.

It is forecast to snow in two days though. There will probably be some usable days left here and there but that means salt on the roads soon, so it's getting time to put it away. If it is a different problem and maybe it has a leak somewhere, I don't want to bring it up to them months from now.

 

My overflow tank is virtually always empty. It's just a dumpster for excess coolant. I wouldnt worry about it at all.

 

with the others....And I'd as that you might give THIS a read. You can idle the car all day and it won't get hot enough to turn the water in the exhaust in to (actual) steam.

 

Sorry, Fauee, that's not the right answer. There should always be some coolant in your recovery tank. (It's not an "overflow" tank.) If your recovery tank goes empty, your radiator will be low on coolant, and air will be drawn into the radiator as the engine cools off. This will promote more corrosion in your engine due to the excess air and oxygen mixing with your hot coolant.

If there are air bubbles in the cooling system after a coolant change, they should automatically be pushed into the recovery tank as the coolant expands. As the engine cools off, fresh coolant will be drawn into the engine to replace the expelled air, so it's important to check this after a coolant change. Some engines have additional bleed valves to purge excess air from the cooling system as the engine warms up.

This is from my FSM:
"Any air or vapor in the cooling system will be forced to the coolant reservoir under the liquid level and leave through the vent on the cap of the reservoir. As the system cools, the extra coolant in the reservoir will be drawn back into the radiator through the vent valve (in the radiator cap). In this manner, the radiator will keep itself full at all times."

This also requires that your radiator cap have the three sealing areas working properly.

 

Thanks for that. I forgot to mention that when I got to the shop I checked the exhaust and the steam had stopped, invisible exhaust.

Hoping to hear tomorrow that it was some air in the cooling system and it just needed to expel it. Will update.

 

 

Hmm, it would seem hard for the radiator to get this air in it. The overflow tank up front only has one connection on it, connected to the highest point of the expansion tank (by the firewall). Even if it pulled air into the expansion tank, the radiator is still FAR lower than that. To avoid sucking air from the fron tank to the back, youd need a lot of coolant up front, and honestly I don't think youd get enough suction to pull the fluid that far from thermal contraction.

 

Hmm, it sounds like we have a communication problem here. The OP has an '87, and I'm guessing you have a later model, since the '87 does not have a tank by the firewall. Here's a link to the '84 - '88 (+?) set-up. https://keenparts.com/pages/Catalog3...&diagram=14535

Does your owners manual or your FSM say anything about keeping your expansion tank (by the firewall) filled with coolant? What year do you have?

 

I have a 92. That would make sense as to why its different! To be honest, I've never looked into it much, it's totally possible its plumbedwrong, my car had a heater bypass and stuff, so it had been messed with.

I was half thinking that mine had been modified and that's why it was different.

 

HRR is right....and even on the '92^, the surge tank (by the fire wall, w/the "radiator" cap) should be totally full all the time. As the system heats and coolant expands, the overage should move into the recovery tank (under the headlight). Then as it cools, it will draw that coolant back into the surge tank, keeping the cooling system totally full and free of air.

It operates just like the older system...only the radiator "side tank with the cap", has been moved up to the firewall...most likely to help get air out of the system easier than the older system, where the "radiator cap" was at a lower elevation the some other parts of the system.

 

Shop said they did a block test and the head gasket is good. Couldn't find a leak. Must have just still had some air in it. I will keep an eye on it next year.

Thanks for the advice!

It was raining pretty hard on the way home and it looks like it has developed a small leak in the passenger door or the roof weather stripping. No big deal, just a few drops but I need to fix it or replace the stripping for next year. Never ends does it?

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If there are no air leaks in a vacuum system, you can lift water about 20 ft. Atmospheric pressure at sea level is about 14.7 psi, which will "push" the water that high..