Overheating?

Ok, this might be a stupid question... what actually happens when your car overheats? I sat in my jeep tonight messing with the new deck i installed for about 45min or so. it was hot outside, so i had the ac on (not full blast or anything) and i kept watching the temp guage to make sure that it didn't get too hot. it barely moved past the middle of the gauge, so i figured i was fine.

when i got out of the jeep, there was a huge puddle of coolant underneath... does that mean it overheated? it seemed to be coming out of the resivour. i thought that when your car overheats, the needle on the temp guage is supposed to give you some warning??:huh:

No, was doing it's job. When shes hot like that she will overflow into the resevoir preventing heat pressure. But you might wanna make sure your water pump isn't going out because I have never blown water from the overflow and I've had mine very very hot.

btfury said:

Ok, this might be a stupid question... what actually happens when your car overheats? I sat in my jeep tonight messing with the new deck i installed for about 45min or so. it was hot outside, so i had the ac on (not full blast or anything) and i kept watching the temp guage to make sure that it didn't get too hot. it barely moved past the middle of the gauge, so i figured i was fine.

when i got out of the jeep, there was a huge puddle of coolant underneath... does that mean it overheated? it seemed to be coming out of the resivour. i thought that when your car overheats, the needle on the temp guage is supposed to give you some warning??:huh:

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45 min idling with the AC on would have left a huge puddle underneath of WATER (condensate from the AC) coming from the passenger side firewall. . . right about where the coolant overflow bottle sits. . . .

3XJFamily said:

45 min idling with the AC on would have left a huge puddle underneath of WATER (condensate from the AC) coming from the passenger side firewall. . . right about where the coolant overflow bottle sits. . . .

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I'll second that one-- also make sure the overflow bottle wasn't overfilled-- the coolant expands when hot and if it was already full, it'd have nowhere to go but out.

--Shorty

If you find that it actually was coolant, then I would get a new 16psi radiator cap. Realistically it shouldn't have boiled over unless it got really really hot, and if your guage is correct then it doesn't seem like you got it hot enough for it to boil over unless the cap is bad.

However, I agree with these other guys that what you were seeing under the truck was most likely condensation dripping from the A/C system.

it was definitely coolant... and it definitely was coming out of the resivour because the level was low this morning... but it was fine in the radiator. could i have possibly just had too much coolant in the resivour before? so it heated up and had no where to go but the engine temp stayed low?

If it was definately coolant, then you most likely just need a new 16 psi radiator cap. It should only boil over like that, when it is REALLY hot. if your guage didn't ever read hot then it shouldn't have boiled over. Unless your guage is shot.

You have to remember the gage just checks a very small area in the back top of the block (or where ever it is in the 2000 XJ). There are hot spots in any motor that may get a whole lot hotter than the gage shows. Also aggravating the problem is different temperatures of coolant don't really homogenize well, they tend to stay separated.
When one of the hot spots gets hot enough to boil the coolant, you get steam. This can cause all sorts of immediate and even fairly long term problems. The steam (air) doesn't purge well.
The first thing I do when my temperature gage starts creeping up is to rev up the motor some. This increases air flow from the fan and also increases coolant flow from the pump.
The recovery bottle spewing is often a sign of air in the system someplace, like mentioned a faulty radiator cap or an overfilled recovery tank. It can also happen when there is a pin hole leak someplace in the system. The system doesn't purge air well and a little sucked into the system during every motor off cool down cycle. It can add up until it causes major problems, like a partial air block, that just causes more steam by restricting flow.
The rubber hose between the cap and the recovery bottle is also a good place to check periodically. Any cracks or poor sealing is going to cause the system to suck air and not recover coolant like it is supposed to do.

This may be a stupid answere:farmer: , but considering the questione, make sure you're not over filling the reservoir. There should be a "cold" and a "hot" line on the bottle. Check the level in the morning. It should be at the low level line. Do not add to this! If you do, you stand a good chance of "boiling over" when your engine is at operating temps. With the engine "hot", like it is just after getting off the freeway, the water level should be near the "hot" line on the reservoir; that would be normal.

not a stupid answer, i think thats exactly what happened... i must have overfilled it before... stupid mistake