Losing Coolant and dropping oil pressure gauge

The coolant loss is serious, and if there are no puddles under the vehicle then you have a blown head gasket or similar problem. You can buy a spark plug to air compressor adapter, pressurize your cylinders, and watch for bubbles in the coolant. You can check for a sweetish smell at the exhaust. If you pressure test the cooling system, this won't necessarily find your head gasket problem, but it will eliminate the possibility of an external leak.

Oil pressure drop at idle is expected, but not enough to trigger the check engine light. You can rent or buy a mechanical pressure gauge to verify that your dash gauge is or is not the problem. If the gauge is accurate then you have a mechanical problem, such as a worn oil pump, bad bearings or stuck pressure relief valve.

Good luck.

Earle

I agree with Earl. The coolant issue is serious; on gallon per month is very serious. It's going somewhere, and you must find out where. I've seen test strips that when dipped in the coolant, indicate the presense of hydrocarbons, a telltale sign of a blown head gasket. Doing a leakdown test will usually pinpoint this as well; a drop in pressure followed by a visual examination into each spark plug hole will tell you where the head gasket has been breached. Either way, you should repair the problem or have a mechanic do the work for you. This is unusual for a 4.0 engine.

The 'check guages' lamp usually indicates a faulty dash guage. They are expensive to replace, but I would do it regardless of cost. You can first check for proper oil pressure by hooking up a mechanical oil pressure guage and comparing the readings.

If this were me, I'd just find a very good mechanic and have everything fixed all at once. You're probably looking at 5-$700 for everything, with most being labor. You bought a very good quality truck: it's worth the bucks to have it fixed right.

Something just dawned on me. If you do a key-on check of the dash guages (key off...press and hold odometer button, key on, release button), the OBD-II system will first flash codes on the odometer readout, then systematically test each guage as you watch. Pay attention to the oil pressure guage; if it isn't working right, you will probably be able to tell right off this way.

That is...if the 2000's are anything like my 2005 TJL. I'm pretty sure they use the same test procedure.

My Chemistry is a little rusty, but doesn't this happen too?

H2O + CO2 HCO3- + H+

If you're bubbling CO2 through your coolant, that's not so good then. Btw, I put some Zerex G-05 in the Jeep. I'm still thinking about what to put in the Suburban.

Cheers,

Earle

Appreciate all the posts, well group here are some results:

The pressure test indicated a very very slow drop in pressure but didn't reveal any external leak source, so it's definately internal

All the plugs look fine and identical in wear

The exhaust seems ok as well and is not abnormal white or smelly

The sparkplug compression test is a good idea but I am less an air compressor

Where do you find the coolant strips to test for gases?

I am going to run a bottle of Bar's Leak in and then recheck the pressure, hopefully that will seal up whatever it is as I have had good luck with there product in the past....

Tom

Earle Hort> My Chemistry is a little rusty, but doesn't this happen too?

These are rarely sold to the public; best solution is to drive on over to a local radiator shop and ask them to test for the presense of hydrocarbons.

This is a band-aid on an amputated limb. Radiator salesman love Bar's Stop Leak. You can try it, but then be prepared to shell out the big bucks for gasket replacement anyway. Then be prepared to replace the radiator if it was marginal to begin with.

I guess I am not convinced that it is the head gasket since there is not anything to confirm this. The engine and trans oil are OK, the plugs are OK hence nothing to indicate a blown gasket yet. The checking for gases would confim a possible head gasket replacement.

If the pressure test holds with the stop leak then it a fix, maybe it lasts for 5 years or 5 days. Additives and stop leaks do work, just about every car manufacturer uses them.

Yes I agree if you have a corroded radiator this may bridge already small corroded passages within the radiator or accelarate the replacement that would be needed anyway.

Looking at $700-1000 for a head gasket makes dropping 3 bucks a calculated risk on a crummy radiator.

Tom

Outatime wrote:

One thing not mentioned is the overflow bottle. If that sucker springs a leak it will drain coolant as you drive then suck air back into the radiator. As the radiator builds with air the boiling point goes down and then what goes out is mostly steam.

The best thing to do is a pressure test. Simple, cheap, and Autozone has the tool on free rental.

If you have to use this stuff make sure that the engine is running when you pour it in slowly, or you could lock up your water pump or jam your thermostat open or closed.

If it is not dripping on the ground, then a gallon a month has to be 99.99% surely a head gasket.

Earle

One thing that I like about overflow bottles, is that they are made out of that kind of plastic that is going to dry out and crack after, say, fifteen years. Then it will be a special order part or no longer available, and of course shaped so that nothing but the exact replacement is going to fit. You might have something here, which is why I said "99.99% sure".

A pressure tester won't find anything wrong with the overflow bottle, as they are open to the air, so that should get a thorough inspection.

Earle

Yea.. not only do they crack but they make the darn things out of a plasic that can't be thermally welded or epoxied. :( I've had some luck with sheet aluminum and rtv/screws.

It will if you use the stopper head from the kit and test the bottle. :)

Guess you could have a new one made.

Checked the overflow bottle and it is fine too. Again did the Autozone pressure test and there is slow dropping pressure but no external leak.

Stop leak is in after running it for about an hour last night. I pressure tested it againg this morning cold and the pressure drop is still there. How long does it take stop leak to work?

Well if it's the head gasket then where is the coolant going then?

Trans and Engine oil are not contaminated with coolant Spark plugs all look okay

It's got me perplexed and at my wit's end so I am taking it to the dealer on Tuesday, Park Jeep here in Burnsville to have them continue diagnosing this and the oil pressure gauge too...

Thanks,

Tom

Earle Hort> > > If you have to use this stuff make sure that the engine is running

Not admitting that I have ever used the stuff, but it generally starts to work immediately. If it's leaking into the combustion chamber though, that is a lot of pressure to contend with. If you have coolant leaking into the combustion chamber, the spark plugs will look OK. In fact they will look a lot cleaner than they have a right to.

Earle

I have all the same symtoms on my 2000 Grand Cherokee 4,0 Ltd.

I know everything points to a head gasket but its twice the price to do here in the UK. Jeep have had my car for 2 days and they say it is NOT the head gasket.

There is no microscopic parts per million of oil in the water or water in the oil but I still get through a litre in 40 to 80 miles with no leaks or loss of power.

Bob

You might have one of those mysterious leaks that only happens when the vehicle is totally warmed up. I have a Chevy truck a while back that was losing coolant. I knew it was a leak because I would see a puddle of coolant on the ground once in a while. A system pressure test showed no leaks. My friend eventually found the leak. (He has a repair shop that is based on AC and radiator repair) The way he eventually found the problem was to pressurize the system with a pressure tester and let the truck run. If I recall, he said it took about 90 minutes, but eventually a small pinhole in the upper hose started spewing coolant. The thing absolutely would not leak until it was at full operating temperature.

Chris

I also had one of those recently. Drove me nuts until I noticed my battery was covered in coolant. Same deal a mini pin hole that would only open up at highway speeds when it was really hot.

Mike

Coolant can leak directly into a combustion chamber after the vehicle is warmed up, without any showing up in the oil. As Chris says, a pinhole leak can do the same. The folks at your garage will likely never see what is going on, unless they allow the vehicle to run for a good time while they observe it. You will be paying their no doubt high hourly rate, to have someone watch the vehicle, but that is how you find problems like this.

Earle

Not only does the engine have to be at full temp and pressurized but at temp long enough to get the hoses fully softened.

Ed had a tiny little split hidden by the radiator clamp. Turns out the hoses were factory from '96. It is lucky he didn't have to walk home...