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post #1 of (permalink) Old 12-09-2005, 05:25 PM
bluecj77
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Cooling situation, looking for advice

I will describe in as much detail as possible what I did. I put a cooking thermometer in the radiator neck to compare the reading to the mechanical gauge in my dash. I let the Jeep idle for a while, occasionally bringing the RPMs up quite a bit. The once the thermostat opened, the cooking thermometer read 180 and never moved. The in dash thermometer read 145. It is a mechanical gauge that takes its reading where the right hand arrow points:
[image]http://img510.imageshack.us/img510/5730/258block3if.pn[/image]
(image stolen from an older post by John_Strenk. Thanks)
Does this mean that when my in dash gauge has read 230, the actual temp has been 265? It seems like it will idle all day but almost instantly hits 230 on the freeway. When I brought the RPMs up I could not see the water moving in the radiator at all. I could however see small collections of little bubbles on the surface (Possibly because I used water from a jug I had been drinking out of? I have never seen this before.) and occasional bubbles rising to the surface. Also, no matter how many times I have changed the coolant, there seems to a very small amount of oil on the surface of the coolant. When I shut the engine down the water started to glug-glug out the radiator neck. Large bubbles rose to the surface. I should note that the water level was pretty high though, right at the bottom of the radiator neck. I am pretty much ignorant, but it seems like I have a flow problem and possibly a blown head gasket. Any tests you can recommend? Any advice would be much appreciated. Thanks.

edit: I can't get the image to work. Sorry. Just paste the adress into another browser window.
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post #2 of (permalink) Old 12-09-2005, 05:41 PM
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Re: Cooling situation, looking for advice

One of the problems with that method is that you don't know that the water coming into the radiator is the same temp as the water where the sensor is....though they should be close.
There is another way to confirm the calibration of the gauge....
Remove the sensor, drop it in a pot of boiing water next to your jeep (hot plates come in handy for this)...If it were not a mechanical, you would need to connect a ground wire to the body...

With the water at full boil, you should see apx 212 deg. Let the water cool and compare the temp readings between it and the thermometer. Most analog gauges are not linear...but, if you have an offset in one dir or the other, it's 'usually' consistant.

As for the high temp problem....if you are slowly loosing water...then, yea, you most likely have a blown head gasket.
post #3 of (permalink) Old 12-09-2005, 07:31 PM
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Re: Cooling situation, looking for advice

This the pic?
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post #4 of (permalink) Old 12-10-2005, 04:06 PM
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Re: Cooling situation, looking for advice

Yes, that is the picture. Thanks.

Yes I do think I am losing water, but very slowly. Is there a way to be absolutely sure about the head gasket besides pulling the head?
post #5 of (permalink) Old 12-11-2005, 06:23 AM
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Re: Cooling situation, looking for advice

There is a tool consisting of a hand pump, pressure gauge and an adapter for the filler neck. You can pressurize the system and let it sit, for days if necessary. Run the test with the engine cold, and the oil drain and spark plugs out. The constant pressure will eventually push enough fluid through the leak to definitively show where it is.
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post #6 of (permalink) Old 12-11-2005, 06:09 PM
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Re: Cooling situation, looking for advice

Couple of questions about that method: I can only put maybe 20 pounds of pressure on the cooling system right? The combustion in the engine has way more pressure to push through a gasket leak. Is twenty pounds guaranteed to make a leak show up, even over a couple of days? Also, a pinhole leak in the radiator could explain the running hot and the losing water right? Wouldn't that potentially give a 'false positive' with the pressure test? I am not sure I would be able to spot the coolant leaking out of a small hole. Also, if it is a head gasket leak and I did this test, I should find coolant in the cylinders? Enough to see through the spark plug holes? Thanks for the help I just want to be sure because any I work I have to do will be done in the cold in a gravel/mud school parking lot. Oh, and is the tool just called a cooling system pressure tester or something else?
post #7 of (permalink) Old 12-11-2005, 09:25 PM
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Re: Cooling situation, looking for advice

Typically, a blown head gasket is a small hole....hence, not much is pushed into the cooling system on the firing stroke....what usually happens is that it sucks water into the chamber.....

Another test is to disconnect your coil, put a plastic bag over the carb and then crank the engine...this will give you max vacuum....pull the plugs and see which one has water on it.

If the leak is bad enough you will also be able to tell by looking at the spark plugs...one of them will be discolored.
post #8 of (permalink) Old 12-11-2005, 10:27 PM
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Re: Cooling situation, looking for advice

It is a cooling system pressure tester. Good ones are pricey, so you may want to borrow one somewhere if you have an in. Even a small leak will show up eventually if you wait long enough. If ir leaks into a cylinder it will show up in the oil or in the plug hole. With all of the plugs out you can turn the engine over with a wrench on the crank pulley bolt. Get the pistons to TDC one at a time and look in. Push a rolled up paper towel into the hole; it will soak up any water and be easy to see.
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post #9 of (permalink) Old 12-12-2005, 12:11 AM
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Re: Cooling situation, looking for advice

A leak can be either way - water getting into the chamber under vacuum or just sitting, or combustion gasses getting into the cooling system. They don't always leak both ways.

Pressure checking often nails it, but there's another way too.
Radiator shops and decent repair shops have a chemical tester - made by Stant.
It sucks the air out of the radiator through a blue liquid chemical. If the chemical turns less blue, clear, or pink, it means combustion gasses are in the cooling system - a leak.
Combustion gasses collect in bubbles - bubbles don't cool, thus causing overheating and fluid loss when the bubbles expand.

Gaskets seal 4 things, combustion, water, oil pressure passages, crankcase. Leaks can occur in any combination and or in any direction.

A small leak in the radiator or hose can pull in air, the air collects, expands, and causes overheating too.

Air, being thinner, can get through where water won't. Sometimes a gasket forms a flap, only opening one way too.
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post #10 of (permalink) Old 12-12-2005, 06:53 AM
 
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Re: Cooling situation, looking for advice

If you send a sample of oil to Blackstone Labs, for $20 (last I checked) they will send you a full oil report, including whether or not you have any coolant in it. I do these reports on each of my vehicles once a year just to check health. $20 buys alot of piece of mind. If you want to be 100% sure before you tear the engine apart, have the oil analyzed.
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