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I have a 1995 Neon DOHC with 165k miles. The current problem is that significant coolant overflows to the overflow bottle on almost every trip and it is never recovered back into the coolant system. After about 20 minutes of driving, there is so much overflow that the overflow tank fills up and coolant is lost from the overflow tank to the ground despite the overflow bottle starting nearly empty; also in about 20 minutes enough coolant is lost that the heater core no longer outputs heat (it does output heat normally during the first 20 minutes) and if I keep driving, then the car will eventually overheat due to loss of coolant. The system does not recover coolant back into the system when it cools down. Typically there is still positive pressure in the system even after letting the car sit overnight. So I have to keep topping off the coolant level in the radiator daily to keep the coolant system full.
I have tested the coolant system with a pressure tester and it holds 16 psi reliably (16 psi is spec). I also tested the cap several weeks ago and replaced it because it was defective. I performed a block test (combustion leak test) on the coolant system, which tests for exhaust gasses in the coolant system and the result was negative. I replaced the thermostat three days ago, but the symptoms remain. I have run the car at idle with the coolant pressure tester attached and observed that as the car warms up, the pressure continually rises. I watched it rise from zero to 19 psi and it was still rising, but I shut the car off, not wanting to blow a coolant seal.
Repair history:
1. Car overheated a few months ago due to loss of coolant from bad water pump.
2. Water pump was replaced with AutoZone water pump.
3. After a few weeks, the AutoZone water pump also leaked.
4. I replaced the AutoZone water pump with a factory water pump and replaced the upper coolant hose (I also tried to replace the lower coolant hose, but the NAPA part didn't fit so I put the original lower hose back on the car)
5. Car still leaks coolant- I bought a pressure tester and determined that the radiator cap was bad (only held about 8 psi, whereas it should be 16 psi). Replaced the cap.
6. Car now leaks coolant out of the coolant reservoir.
7. Replaced thermostat.
My current thought is that the radiator may be clogged to some extent. I have noticed that typically when I do a pressure test on the coolant system, the coolant level after the pressure test will be lower than before.
What do you think?
Answer -
Hi Nathan,
I had one other suggestion. If I am correct and there is a leak between the cylinder chamber and the cooling system at the head gasket area, I have in the past had success in avoiding removing the head by just retorqueing the bolts. This works if there is not a frank break in the gasket but rather a leak due to the head bolts not being evenly torqued and thus allowing a leak. If you want to give it a try, just untorque the bolts to less than step 3 of the torque pattern (just under 50 foot pounds) using the pattern that is the reverse of the tightening sequence, then torque them to 50 foot pounds, and then give them a 1/4 turn (but because the gasket has already been compressed I would begin with an extra 1/8 turn and see if that stopped the leak, and if not then add another 1/8 turn provided that the torque is not excessive to add it). In suggesting these torque values I am using those for the 2.0 SOHC and 2.4 DOHC; I am not familiar with your 2.0 DOHC engines torque specs so if they are different, use those.
I have stopped leaks in a BMW 1.6L and VW 1.8L using this approach. No guarantees but if it works you save a lot of work!
Roland
Hi Nathan,
I am thinking that with the pressure situation being so acute and so quickly after starting the engine, and that you didn't mention concomittant evidence of high temps on the gauge when the pressure is rising rapidly, and that the system doesn't draw fluid from the overflow back into the cooling system...that you have a head gasket leak. Despite the test you did, I wonder if it was done with a working echaust gas test unit. If the system were tight it would suck coolant back into the cooling system when it cooled. Do you see and white smoke from the exhaust, or is the oil cloudy or milky? Those too are manifestations of a head gasket, if the part of the gasket that broke is between the coolant cavity and cylinder chamber area and oil return tube, respectively. That is my hunch just based on how you describe the symptoms and the history. At the mileage you have recorded the gasket going would not be unusual after an overheat experience. I doubt it has to do with the radiator unless you have high temps (steam) coming out the overflow bottle rather than just pressurized warm water. When a break in the gasket occurs between the combustion chamber and the coolant passageway, the engine compression is 'felt' by the cooling system.
Roland
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Roland,
Thanks very much for your prognosis!
I believe you are correct! i.e. that it is indeed the head gasket. After your reply, and a subsequent attempt to drive it, the Neon lost coolant and overheated even faster than it has before. After coming back home, I opened the radiator cap and idled the car. Lo and behold I found little bubbles continually coming out of the coolant. I presume these are exhaust bubbles due to the head gasket leak.
I tried retorquing the head bolts. When I opened the valve cover, I noticed some milky oil coating the bottom of the valve cover though I had not previously noticed any milky oil on the dipstick.
The block test that I mentioned earlier was not done with an electronic gas tester, but with a blue liquid style block tester where the liquid is supposed to turn yellow upon contact with exhaust gases at the radiator cap outlet. Since this test was negative before and I'm positive that I hadn't seen bubbles before, I can only surmise that the head gasket leak was not as bad before and perhaps only exhibited a leak at higher RPMs and resultant higher cylinder pressures; so I didn't detect the problem at idle.
I also am assuming that the pressure test of the coolant system was okay because the gasket may have held 16 to 19 psi, but not combustion head pressures. I was going to attempt a cylinder leak down test and see if I got bubbles or higher pressure in the coolant system, but after your reply I saw bubbles at idle so I didn't bother.
Currently the cylinder head is being pressure tested and resurfaced at a local machine shop. I also found a small 1" long crack in the exhaust manifold. The machine shop advised me to replace this since it could leak air that would affect the oxygen sensor reading. Do you think this it is necessary to replace it?
AnswerHi Nathan,
I am sorry that I was correct, but happy that I hit the mark. On the exhaust manifold, I agree that it will be only a matter of time before a repaired exhaust manifold begins to leak in the same area and then you will have problems with mixture control (O2 sensor thrown off of accurate assessment), gas mileage, and NOX levels preventing you from passing smog, when it happens. You might be able to find one at a local salvage yard and if it is the kind of place that lets you remove it yourself, at a pretty low price compared to new. So good luck with the engine after you get the machine shop work done and reassemble it. Please let me know if anyother fine points come forward that I might be able to share with others. Be sure to clean the surface of the head thoroghly but not so vigorously as to scratch the surface, and vacuum up the crud from the piston tops. Of course follow the manual in all aspects.
Roland
