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1994 Nissan Altima Overheating Issue

My husband and I are experiencing a problem with our 94 Altima that we just can’t seem to get to the bottom of. Here it goes:



-The trouble began a few months ago when the fan started running after the engine is turned off for a minute or two. We didn’t really think anything of it, but are starting to think it might be related to the other issues, so keep it in mind.



-About two months ago my husband was driving it and the car stalled a few times while he was driving, then it started to smoke from the hood. We took it to our mechanic who found that our coolant was low and filled it up.



-A week or so later, the same thing happened, and we took it back. The coolant in our radiator was gone but our overflow tank was full and had not began emptying at all. He checked it out for leaks, etc, but couldn’t find anything. He said we probably had an air bubble when he filled up the coolant. So, he filled it again and we checked the coolant regularly. The car was fine for while.



-This past weekend, we were getting ready to take the car on a long trip (6+ hours). My husband checked the fluids before we left, and the coolant appeared full. However, as we were drving for about 20 miles on the freeway, we started to notice the temperature guage go up. We pulled over, let it cool down, opened the radiator and checked the coolant. Full. Overflow tank, full. We continued driving it about 1.5 hours and decided to stay the night at his parents’ house instead of driving all the way. We had the car checked out by his parents’ mechanic the next day, and they said that we had some leaks in the bottom of our radiator and would need it replaced. The coolant was leaking out the bottom, which is why it had appeared full from the top.



-We got the new radiator and they replaced all of the hoses as well, and that we day drove it another 5 hours. The car was fine all weekend, except the fan was still running after we turned off the car. We thought this was odd since we just had the radiator replaced.



-On the drive back, it started to overheat again about 5 hours into the trip. Keep in mind that we are in Washington State and had driven it over the Cascades there and back without a problem. It was after we had driven over the Cascades that the car started to overheat. We blasted the heat until we made it back to his parents’ house. We checked the coolant level when it cooled–both the overflow tank and the radiator were nearly dry.



-So, we frustratingly took it back to the same mechanic the next morning (that was yesterday) and he checked the system for leaks and there was absolutely no leaks to be found. He said again that it was an air bubble. He filled it back up for us and we drove it home without a problem. The coolant is still full.



So, now that you have all of the history, here are my questions:



1. Why is the fan still running after the car is off? Should it concern us?



2. It appears that only one of the fans is running. Is that a problem?



3. It seems odd to me that an air bubble could cause the coolant to completely drain in only about 14 hours of driving in cool weather. Is there another explanation for this?



3. The mechanic mentioned that if it wasn’t the air bubble, there is a slight possibility that it could be the beginnings of a head gasket issue. However, he is very doubtful since there are no symptoms. It seems to me, though, that the coolant has to go somewhere, and since it’s not leaking out, is it possible that it’s leaking in? Can we know before it’s too late? Should we cut our losses and start looking for a new car?



Thanks for any help you can give. As you can see, it’s been quite the experience for us. Thanks for reading.

  1. The fan is running because the temperature sensor in the radiator is telling the computer that the coolant in the radiator is too hot, and the computer turns the fan on. That’s how it should work, and occasionally it’s OK if the fan comes on after you park the car because the heat from the engine continues to be absorbed by the coolant.

  2. Some cars run one fan to cool the radiator and both fans come on when the AC is on. Open the hood and, with the engine running, turn on the AC. Both fans should run.

  3. An air bubble is just an air bubble. There shouldn’t be air in the cooling system, but if there is it won’t cause the rest of the coolant to disappear.

  4. The coolant can’t go too many places. It can leak out somewhere, in which case you should be able to see it. It can boil over into the overflow reservoir, and maybe onto the ground, but, again, it’s visible. Or it can go through the engine and out the exhaust pipe. This is what happens when a head gasket fails.

Nowhere in your post did I read anything about a mechanic installing a thermostat or a new radiator cap, both of which are the FIRST things that should be done, after checking the coolant level, when there are overheating or under-heating problems.

The mechanic who told you the coolant was leaking out the bottom but still appeared full at the top must have laughed like crazy when you fell for the story. As coolant leaks out the bottom of a radiator it is replaced by coolant from the top, and the radiator appears to be low on coolant. Be that as it may.

There are tests to determine both a cooling system leak and/or the presence of a leaking head gasket. And I’m not talking about visual inspection. The cooling system can be pressure tested, the cylinders can be compression and leak-down tested, and the coolant can be analyzed for the presence of exhaust gasses.

Make sure the thermostat and radiator cap are new, or nearly new, before you do anything else. If they are both functioning correctly, then I’d start having some serious testing done. This is starting to sound like a leaking head gasket.

I forgot to mention that the first mechanic replaced the thermostat because he couldn’t find any other leaks. I don’t believe he replaced the radiator cap, but I’ll have to check with my husband on that one because I wasn’t there. In any case, we have a new one now with the new radiator.

Thank you so much for your advice. Note my correction below about the first mechanic.

So, if it is a head gasket issue, then how long before it goes? Also, what needs to be replaced when a head gasket blows? The engine? I’m not really sure. Should we just try to sell the car now or is it worth replacing things before they break?

Also, about the fan, it runs every single time the engine is turned off, no matter what length of trip (2 minutes, 3 hours, etc). But it usually only runs for about 30 seconds.

I’m confused about the radiator issue because he said he found a leak. It seemed odd to me too but because he is trusted by my husband’s parents, I assumed he knew what he was talking about. I wasn’t there when he gave the explanation though–it was relayed to me through my mother-in-law, who doesn’t know much about cars. Is there another explanation for what he meant?

Thanks again for your help.

Well, after all this I’m pretty sure you have a head gasket problem. What you have to understand is this: Since you’re already losing all of the water in the cooling system while you drive the car, the head gasket has already “gone.” The gasket is leaking, and that is the definition of a “blown head gasket.”

If you continue to drive this way (assuming I’m correct) there could be significantly more damage leading to higher repair costs. You really need to confirm whether or not the head gasket is leaking, but from all you’ve posted here I don’t really see any other explanation.

The original radiator may well have had a small leak. It was certainly old enough. Now that it’s been replaced you can pretty much rule it out as the cause of the overheating problem. The radiator could have been leaking but the overflow reservoir might stay full if the cap were faulty. Perhaps that’s what the mechanic meant.

They probably installed a new cap with the new radiator, too, so I’m not going to worry about that anymore.

There’s no way to know exactly what, if anything will need to be replaced along with the head gasket until the head is removed from the engine and an internal inspection can be done. I would want a new water pump, if nothing else. You didn’t say how many miles are on this car, so I can’t venture a guess as to its condition.

Based on the car’s age I suggest you get a repair estimate (after confirming the head gasket as the cause) and decide whether or not you want to fix it. This is not an inexpensive repair, but it will cost less than buying another car, and Altimas of this vintage have been known to last a LONG time.

I’ll emphasize what McP said…you need to have some actual testing performed. I agree that you may have a bad headgasket.

Perhaps this will help you understand the problem…
Around your cylinders is a water jacket through which your coolant flows. The space where the head is bolted to the block is sealed with a gasket called a “head gasket”. If a breech forms between the cylinders and the water jacket, two things happen:

  1. hot combustion gasses get blown into the water jacket, heating the coolant beyond the radiator’s ability to disspate the heat and the engine overheats
  2. every time the piston goes down to draw in fuel, the vacuum also draws in coolant through the breech. This coolant then gets vaporized and blown out with the exhaust.

These are what is apparently happening to you. Unrepaired, the breech will grow larger via erosion, the engine will overheat and parts will warp, and the problem will grow worse. Additionally, the oil passages can become invloved, the oil can become contaminated with coolant, and your bearings can get destroyed.

Have the compression leakdown test as McP suggested.

Thanks so much again for your reply. It’s great that you’re willing to put so much time into helping people on this forum. I’m going to take the car in tomorrorw and get the diagnostic test done. The mechanic who replaced the radiator said that the water pump is fine. I’ll ask our mechanic tomorrow. The car has 130,000 miles so I do feel like it has a lot of life left in it, and it has had recent updates done as well (breaks, suspension, CV joints, maybe clutch and timing chain from the previous owner?), so you’re right in that it might actually be worth it. In your opinion, with the milage and the updates, is it worth it?

Thanks again for your help!

If the car is in good condition overall, which your post suggests is the case, I would repair the head gasket (assuming that’s the problem) and drive it for another 130,000 miles.