Slight Drop in Coolant

So I've been driving the heck out of the XJ lately going on various job interviews up to 110 miles away from home. I've got a 2wd 98 XJ with the AW4 and I've noticed a very minor drop in the coolant level. I had the overflow container filled to just under the highest hash mark on the bottle. After giving the XJ a couple of days off from driving, I checked the level and it was down to right between the lowest and highest hash mark. The coolant had been filled when the block was cold so this shouldn't be the normal up and down movement due to water expansion. I added probably 2 cups of water to the bottle to get it back up to just below the highest mark on the bottle.

Should I be concered? I've daily driven the XJ for 2 years now and from day one I've had a very faint coolant smell when walking outside the vehicle after its been driven. I've had the cooling system pressure tested and no leaks were found, although the pressure test was about a year ago. The radiator and T-stat are new within a year. The XJ has 152k on it, I bought it with 133k and I don't know when/if the water pump was ever changed. I have zero drivability problems and the engine runs steady right under 210 on the gauge. Oil pressure is on the low side of what's acceptable, but within spec and hasn't changed since I've owned it.

I know I might be anal here but I need it to last me another 2 years, so I want to catch anything early before coolant eats my bearings. Since the oil pressure gauges on the dash aren't very reliable I'm slightly concerned about where to go from here.

Thanks for any suggestions and happy Jeepin'

Check for milkshake on the dipstick and oil cap.

Since the smell is outside the engine I would bet on a pinhole leak somewhere, or maybe a water pump bearing seal leak. As long as there is no sign of coolant in the oil I would not worry about it unless it gets worse.

Thanks for such a quick reply. No milkshake on the dipstick or under the cap. I check the oil level more regularly than I check the coolant level. I'm running Mobil 1 synthetic 10w-30 for high mileage engines with a MOPAR oil filter.

After dark, after fully warmed up, Shut off engine and with a bright flashlight- Look all around the radiator, hoses, etc.
Looking for a fine mist,or steam cloud from a tiny pinhole leak.

Also check weephole on the waterpump. Any wet spots at bottom of radiator ends.

Good Luck,
Orange

kastein said:

Since the smell is outside the engine I would bet on a pinhole leak somewhere, or maybe a water pump bearing seal leak. As long as there is no sign of coolant in the oil I would not worry about it unless it gets worse.

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I completely agree with the others.

I just went through about 6 months of a faint coolant smell and minor coolant consumption on my 99, and it finally manifested itself as a radiator leak.

Your 98 has the 0630 head which is very hardy and not prone to the same "cracking" as the 0331 head equipped on the 00-01 XJs are.

The most likely suspect for you might be the "start" of a waterpump failure. Keep an eye on it and if it is the pump, it will start to leak from the weephole which means time to replace.

Thank you everyone for the help and suggestions. I think the water pump may be the most likely suspect. The radiator was replaced one year ago almost exactly so I'm not very suspicious of it, although I won't rule anything out. I've also heard that the older style clamps can fail over time and allow the hoses to seep during warmup and cooldown cycles. Since I don't know when the waterpump was replaced, I'm going to watch it closely and assume it's original. This Jeep has been babied, even before me, so the miles are easy and it's not been abused. I've been reading up on waterpump replacements....(thanks again to the fine people at ) so its defintely something I'll tackle on my own when the time comes.

Good advice given already. I would add throw a new radiator cap on, no lever junk just a plain cap, but use a 16 lb cap instead of the 13 lb cap the counter monkey will want you to buy. If the counter monkey can't figure it out, go to a different parts store.

Thanks Joe. I did replace the cap (taking your advice at the time) with a 16lb at the same time the radiator was replaced. She runs flawlessly and holds temperature perfectly. It never even begins to run hot and the aux fan kicks in well. I also get perfect operation from the heater and no coolant smell inside.

You've checked the overflow bottle and the hose to it thoroughly?

my 99 has a small drip from the bottom of the thermostat housing. however, a few months back the hard hose off the top of the waterpump rotted through...and after that the upper radiator hose had a pin sized hole on the bottom as well...so, could be anywhere...

My 96 is doing the same thing, adding a few cups every week. No visible leaks, etc, so I'm suspecting the heater control valve. Vacuum on one side of its diaphragm, and coolant on the other. I've had it happen on other vehicles. It's an invisible leak.

islandboy312 said:

My 96 is doing the same thing, adding a few cups every week. No visible leaks, etc, so I'm suspecting the heater control valve. Vacuum on one side of its diaphragm, and coolant on the other. I've had it happen on other vehicles. It's an invisible leak.

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If you suspect a heater control valve, get it out of there....they aren't expensive.

They were "underbuilt" from the factory and have a habit of suffering plastic disintegration, when they get old, which leaves you with a major coolant leak and a possible overheat.

Mine did that to me. Fortunately it was because I looked at it funny while changing my spark plugs, so I was able to throw together a quick bypass tube made out of 1/2" copper water pipe that kept me rolling for a few months (during the summer) while I decided what to do. Ended up paying 5 dollars for a brand new valve that I happened to spot in a C4C XJ.

FYI, as JrTxJ noted, the hard hose / steel tube screwed into the water pump that goes to the heater core likes to rot out, and frequently the threads strip when you unscrew them from the old pump. Save yourself some stress and pay 5 bucks for a new one when you buy the water pump; rockauto has them and so do most parts stores.

correct me if I am wrong but the heater core valve is no longer on 98+ XJ`S? I am having a slight coolant leak issue and just trying to factor where its coming from.

willsmysticcobra said:

correct me if I am wrong but the heater core valve is no longer on 98+ XJ`S? I am having a slight coolant leak issue and just trying to factor where its coming from.

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If memory serves me, the heater control valve was found on 84-96.

97-01 do not have this valve.

birchlakeXJ said:

If memory serves me, the heater control valve was found on 84-96.

97-01 do not have this valve.

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You are at least partially correct, 97-01 do not have it. I know 91-96 have the plastic one, I am not sure what 87-90 RENIX jeeps have but I think it's a metal one built into some crazy pipe contraption for the closed system overflow bottle, and I have absolutely no idea what the 84-86s would have.

kastein said:

You are at least partially correct, 97-01 do not have it. I know 91-96 have the plastic one, I am not sure what 87-90 RENIX jeeps have but I think it's a metal one built into some crazy pipe contraption for the closed system overflow bottle, and I have absolutely no idea what the 84-86s would have.

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84-96 should have a coolant control valve (for the heathens, a heater control valve) regardless of open or closed system. As Kastein pointed out the closed system vehicles have a weird valve with extra lines to the pressure bottle. OEM Renix era valves were metal, but replacements today are plastic.