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Earlier today I left my mom in the car with the a/c on (not overheating at the time, 82f outside) to get some groceries. About 4-5 minutes she calls my phone and tells me my car is banging loudly (no pun intended). I run back to the car and hear what sounds like a misfire or One of the cylinders aren’t firing at all. The temp gauge was all the way by the hot mark and the temp/coolant light was on and i can hear somethinng boiling under the hood. Anyhow, I quickly turned off the car and waited about 3 minutes before I restarted the car. It started faster than usual but there was no sign of overheating (gauge was on the normal mark, nothing boiling) and no rough idle. I do have a check engine light on now though. I’ll get it scanned and repost with the code. In the meantime, does it sound like my thermostat needs to be replaced?
I’ve had minor overheating issues before but it only goes over the normal mark just a tad bit, it it’d go back down after I the ac back off. I only have overheating issues withe the a/C on
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What kind of car and how many miles on it?
Overheating with the A/C on (assuming the coolant is full) is often due to bug clogged condenser, clogged radiator, or a radiator cooling fan that is dragging or not cycling on as it should.
Usually cars that have overheated will continue to run after you turn them off .This is caused because the inside of the engine is so hot that the least amount of pressure causes the gas to fire and continue to run for a second or two.
Not sure, but the misfire you observed may be due to pre-mature ignition due to the high heat that resulted in the pistons firing in the wrong order.You could have also overheated it to the point you blew a head gasket. Check for possible water in your oil or oil in your water. This is a pretty good way of knowing. Otherwise check the compression of each cylinder
The bad news: Now that you have overheated like that, you may well have blown the head gasket. Keep careful track of your coolant level, and if you find yourself needing to top it off from time to time that is a sign that the head gasket may have blown, and you will need to test the cooling system for it’s ability to hold pressure, as well as do a compression test, and perhaps a leakdown test. When I did mine none of those tests revealed the bad head gasket. I didn’t find it until I started the engine with the pressure tester on the radiator, and saw the pressure in the cooling system skyrocket.
The good news . .. often, overheating with the AC on is a simple fix. Clean the bugs and leaves from the front of the condenser. Check between the condenser and radiator too. It is an nearly impossible place to access on most cars, and yet bugs and leaves manage to find a way in there.
Check that both fans (assuming you have two, some cars only have one) are running, and running at proper speed when you turn on the AC. There is a pretty fair chance that you will find a problem with one of the cooling fans. One is working good, the other isn’t. There is plenty enough air flow to cool the engine, but not enough to handle the added heat of the AC system.
I looked at the condenser yesterday and saw that it was totally caked up with dirt (literally, as if no one ever bothered to clean it since the car was bought.) That somewhat helped but I was still going up 3/4th way on the temp gauge, so I bought it back home. Looked at the coolant and it was literally way below the line, like barely anything in the reservoir. I thought I’d only need a little bit, but the darn thing took 1 1/2 gallons of coolant. I haven’t got any overheating since then.
Does coolant evaporate/burn as time goes by?
Coolant doesn’t really evaporate. It’s a 50/50 mix of ethylene glycol (or something similar) and water.. and glycol doesn’t evaporate.
If you’ve had to put in 1.5 gallons, those 1.5 gallons had to have gone somewhere.
I’d really recommend starting to look at your head gasket, oil, and the like.. as with that bad an overheat, the head gasket really IS sounding likely. Possible warped heads, too.
-Hinoki
If the head gasket is blown, and with a known overheat, and 1.5 gallons of coolant vanishing, that is a strong possibility, it likely will not overheat as long as you keep the coolant level up. What will happen is that over a course of time (could be just a few miles, could be days or even a week or longer) the coolant level will drop, and then eventually when it is low, you will begin overheating again.
Do sort out the problem with the AC. Make certain you are not overheating when you turn it on, and then check your coolant super frequently, and when you notice that it keeps going down make sure there are no external leaks, and then get the car checked out for a bad head gasket.
[quote=”Moonlight” post=67604]Usually cars that have overheated will continue to run after you turn them off .This is caused because the inside of the engine is so hot that the least amount of pressure causes the gas to fire and continue to run for a second or two.[/quote]
Very true on old carbureted engines, I don’t believe it to be the case with modern fuel injected engines, since turning off the ignition also turns of the ECM and stops the injector pulse, there shouldn’t be any fuel in the combustion chambers to cause run on.
Well, I don’t believe it is my head gasket. After doing some more research, the Lincoln LS (all years) are known for hairline cracks on the Degas bottle causing the coolant to leak out. I’ll be replacing it soon and posting back with the results. Thanks all.
On an unrelated note, I’ve been having issues where my RPM dosent drop back to ~800 like its supposed to after I come to a stop using the brakes. It likes to hover around 1K unless I hop off the brake and hop on it again, only then it would drop back to 800RPM. Any ideas? It gets really annoying since sometimes when I hop on the gas pedal the RPM’s go up like a rocket ship.
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