Elantra coolant leak

Hi all....
I'm having a weird coolant problem with my Mom's Elantra. I believe it's a 96 model.
Over the past few weeks she had noticed the car overheating. I didn't
have much time to work on the car so I just kept filling up the reservoir and the rad with fresh liquid until such time that I was able to spend some time on the problem.
So I got into it last night. I briefly pressurized the system to about 30 PSI (probably too much) and found a small leak on the output of the thermostat. I fixed it by replacing the original hose clamp with a garden hose clamp, thightened it and the leak was gone.
So I topped up the rad and the reservoir with water and off I went for a test drive. The outside temp was about 70 degs at the time. Within about 5 minutes of driving, the temperature gauge sat in the center of the scale. Another 5 or 10 minutes went by and both rad fans came on (stopped to doublecheck), which I found weird since my Saturn doesn't do that unless it's hot out and I'm stuck in stop and go traffic. The needle sat pretty much in the center except for a couple of occassions when it went a little higher, but then dropped again.
When I got home, I let the car cool down and noticed it was missing about a quart of water. Oil appears to be fine, there is no coolant smell in the car when running the heater, and the car doesn't blow white smoke.
Pressurized the system again but could not find any evidence of a leak anywhere.
One thing that I have noticed (not sure if related to the above problem) was that the engine ran a little rough when stopped. The SES light in on constantly except for a couple of times it would flash when stopped at a light. Again, I'm not sure if it is related.
I will be getting a scan tool to check for errors in the next couple of nights but until then I'm confused as to where the coolant might have gone.
Any ideas I should look into would be greatly appreciated.
Thanks Alex
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The flashing check engine lamp will only occur when there is a misfire, so I'm figuring you'll have a misfire code at the very least. As far as the coolant, there are two main possibilities:
1. There was an air pocket in the system and it moved to the top. 2. The head gasket is leaking, possibly contributing to the misfire.
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Thanks for the info Hyundaitech... couple of questions:
1. If the leak contributed to the misfire, would I not see foaming in the reservoir? 2. As above, would the engine misfire all the time or when stopped only? The car runs great when it's moving. There are no misfires and the engine is very peppy. No hesitation whatsoever.
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1. Probably not. Perhaps some bubbling when the engine got hot. A better test is to pull the plug on the offending cylinder and have a look at things. A clean combustion chamber is a sure sign of water/coolant in the combustion chamber. 2. It all depends on how bad the failure is. You're in a high vacuum situation at idle. But, don't dismiss other causes. The ignition system is the #1 cause of misfires, but typically is worst under load. On the other hand, you may have a leaking intake gasket. That'd potentially cause a significant misfire at idle and nearly no misfire off idle.
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Unfortunately (for me) you were right on both fronts. I scanned the computer last night and it showed misfire on #2 cylinder. So I went to take the plug out to see its condition. In order to remove the plugs, I had to take the top cover off but first I had to unscrew the oil cap. Soon as unscrewed the cap, I looked underneath it and didn't need to proceed any further.... saw the light brownish deposit which obviously meant coolant in the oil, which probably caused the misfire, etc, etc....
Now... this is a 4 cylinder Elantra. I guess I'm looking at the head gasket, eh?
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Don't assume the stuff on the oil cap indicates coolant in the oil. In fact, even when severely overheated, Hyundai engines/head gaskets rarely fail in that way. Most frequently, this milkshake-type goop is the result of short trip driving that causes condensation and doesn't allow it to burn off.
Now for the bad news. If your head gasket is indeed leaking, you'll probably need a cylinder head. Very, very rarely do I see a case where a head gasket leaks from overheating and the head isn't warped beyond repair.
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To be honest with you, my Mom driving is pretty much limited to short trips. The oil cap isn't fully coated with the brown stuff and when you inside the rocker cover, the oil appears to have a typical oily color. I guess the best way to really make sure is to simply drain the crankcase a little and make the diagnosis then.
Incidentally, with all the water the car is going through, you would think that the oil dipstick would reflect an increased volume of oil and water, correct?
Also... is it possible that there would be no white smoke out of the tailpipe if the car would be going through a quart of water in a 45 minute trip?

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No. As I said previously, this is not the typical cylinder head/head gasket failure mode on this engine. If you have a head gasket problem, the coolant is most likely leaking into the the combustion chamber, not the crankcase.

Again, this depends on the size of the leak. Maybe.
Once you know what cylinder is misfiring, pull that plug. Rotate the engine so that piston is at the top and look down in with your flashlight. If the piston is clean, you have coolant leaking into the combustion chamber. If it isn't clean, you should probably revisit more typical misfire and cooling system diagnosis procedures.
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Did a couple of things today. 1. Drained some oil from the crankcase. No trace of water in it, so you were right about the cap. Whew on that one.
2. Pulled the offending plug and sure enough she was wet, so this is where the coolant is going into.
Now a million dollar question: head or intake manifold gasket? Didn't have a compression gauge handy so I couldn't check. Will do that tomorrow. I'm also planning to pull the intake manifold tomorrow to check on the condition of the gasket there.
Thanks for steering me in the right direction.
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There's no coolant in the intake manifold, so it won't be coming from there. Unless there's something really weird going on (such as cracked head or block), the issue is with the head gasket. Expect that when you pull the head, it'll be warped beyond repair.
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Bad news indeed.
I don't think I'll bother with it then. The car isn't worth the trouble and/or the expense. Too bad because it ran quite nicely.
Thanks for all the advice and pointers.
Alex
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