Won't cause over heating. The nose plays an important part in being a mechanic. Coolant steam and oil have completely different smells. Coolant has a sweet smell to it. If you have the combination of steam and your gauge shows hot there's a good chance the engine's running hot.

For a start when you can and with the engine cold start looking real good for leaks. Above and below. Check the coolant level. See what you can find.

 

Sounds like a thermostat to me. That's an easy one. Look at the condition of the hoses to and from the radiator. Take a look at the hoses that run to the heater core. If any hoses are in rough shape, now is the time to change them. I suggest what I call a 'basic tune up' on the coolant system. Inspect and replace hoses, change the thermostat, swap the radiator cap (it is a wear item), flush the coolant and refill with fresh coolant mixed with distilled water. Sounds like a lot of work, but it's simple work that any Joe can complete in the driveway in an afternoon. Find a youtube video, should guide you through it.

If you still have overheating problems at that point, you only have three options left: radiator, water pump or fan. Radiators get plugged up (that's why I suggested the coolant flush). Water pump impellers wear out, I'm not sure how to trouble shoot that. Haven't had to deal with a bad water pump impeller, mine failed due to bad seals leaking. The mechanical fan has thermostatic clutch on it, those fail sometimes. Testing them is fairly simple, search the forum for test procedure. The electric fan should come on when the AC is on and when the temp goes above 210. That's an easy one to test, turn the AC on and see if the fan comes on. Next time it overheats, see if the electric fan is on.

 

Thought it might be possible that when removing hoses to changing the valve cover gasket, air might've gotten into the system, messed with the pressure, etc. So, this morning I added coolant via the hose, resulting in short-term good news but possible long-term bad news.

My XJ has definitely leaked coolant at some point. It accepted 1.5 gallons of coolant before it was fully topped off. This remedied the overheating issue for the time being, but I'm left to wonder where that 1.5 gallons of coolant went in the first place. I haven't found any coolant on the ground around the truck since I've owned it, nor can I find any fresh coolant where it shouldn't be in the engine bay.

This being a '00, my fear is that I've got the head crack and coolant is flowing out the exhaust. Going to look into having it pressure tested this week.

FWIW, I took off the oil cap and looked around as best I could, and I didn't see any greenish tint or obvious cracks.

 

You can buy the tester used in the video at just about any auto parts store fairly cheap.

 

Haven't driven the XJ since the one trip down the road after I added the gallon and a half of coolant. Put some cardboard underneath it, and there appears to be a pretty slow drip of antifreeze. I found one fresh drop on the bottom of the oil pan; guessing it's hitting somewhere on the top, then slowly running down the side.

Any thoughts?

 

Identify source. Fix leak.

 

I didn't do a great job of asking my question in my last post. I'm not going to get my hopes up, but I want to take the present leak (and location of the leaking fluid) as a good sign. Coolant seeping through a crack in the head would either pass through the cylinders and into the exhaust, or mix with the oil in the motor, correct? Is there a way that coolant from a head crack could wind up on the outside and bottom of the oil pan?

 

Gotcha. Had me wondering about you.

I don't think the coolant would leak externally from a head gasket. But I have no first hand experience with that situation to state it as fact. The amount of coolant you are losing, I would look for a major leak. Bad hose, or the water pump would be my first thought. The water pump should have a hole on the back of it that will leak when the pump goes bad. It is designed that way. Find the hole, may need a mirror, and look for fluid coming out. Start it and check then also.

 

That's where I'm stumped: I haven't owned the XJ long, and I'm not sure how much of that gallon and a half has been lost since I've owned it. I haven't actually seen a major loss with my own two eyes. It could have been lost over time at the same rate that I'm seeing now, or I may find a sizable puddle in a few more days. Either way, thanks for the suggestions. I'll give the water pump a look tomorrow. Still going to try to have it compression tested this week, too.

 

The coolant system is pressurized when the vehicle is running. Therefore, if you have a leak when the vehicle is off, it will be much worse when the vehicle is running. The little bit of fluid you have seen in your driveway is only the tip of the iceberg. The other gallon or so is on the road wherever you drove it.

 

Of course. Should've thought of that. I appreciate your patience with me.

Wrt the temperature making the quick jumps and drops, I've noticed a few people have claimed that the gauge isn't necessarily meant to be pinpoint accurate, and should be thought of as more of a general indication.

A.) Is this true? Because if so, does that also apply to the speedometer, fuel gauge, etc.?

B.) If true, are more accurate aftermarket gauge systems available?

 

Stock gauges of any type are not 'dead nuts' accurate. For what you're doing, they are close enough. The gauges are there to point you towards an issue. Precision isn't necessary. You can verify your speedo with your phone w/ GPS app.

As far as patience, you're good. I enjoy helping guys figure their stuff out.

 

bad_idea has listed pretty much every place to check for, I think it would be a great idea to wipe everything down, start the jeep and inspect the engine bay. Look at the thermostat, water pump, make sure to check the weep hole on the water pump, check the ends of every hose, and look over every inch of the radiator. When I first overheated mine, I found nothing until I had it pressure tested by a mechanic friend. Coolant started gushing out the radiator onto the front half of the engine. A video might also help you and also the forums.

 

Update...

Had a compression and pressure test done on the XJ today. The compression test resulted in good news all around; looks like there's no issue with the head. The pressure test confirmed bad_idea's suspicion: I need a new water pump. Gonna replace that (and the thermostat and radiator cap while I'm at it), then I'll hopefully be in the clear for a little while.

Thanks for all the great info and help along the way, everyone.

 

just wondering, did your jeep overheat before you took it to the mechanic? then all of a sudden your 1 1/2 gallons short of antifreeze? after? scratch that, I remember changing my rad fluid and found a pinhole in my bottom hose, that I'm sure was there for a while and no bad overheating before I changed it, or after. another time I changed it and left an air bubble in it and had instant overheat. had to burp it and pour more in.