missing antifreeze

I have a 1998 tahoe with 71000 miles. Recently the engine began to tick when starting it in cold weather. When the truck warmed up the noise was gone. I had my oil changed last week and the tech told me I was low on antifreeze and he refilled it. I checked the antifreeze a couple days later and the expansion tank was empty and the radiator was 3/4 of the way full. Not knowing how he filled it, I refilled it myself and drove it to see how much fluid would stay in the expansion tank. I checked the level over the last three days and it seems to be dropping slowly. There is no sign of a leak. Today when I was leaving work the engine was making a much louder ticking or rattling noise which stopped again when the engine warmed up. Tonight I changed the oil to see if my missing antifreeze was getting into the oil. I only got 4 1/2 - 5 quarts out of the engine so I don't think it is going in there. Sorry about the long post. My questions are, where could the antifreeze be going and what could be the cause of the noise at startup. The engine made similar noises in a 60 degree garage tonight after changing the oil.
thanks
tom

Mine also makes the clicking noise during a cold start, which goes away fairly quickly (a minute or two of running).

I spent an exceptional amount of time trying to locate an alleged coolant leak, and right before I was about to take it in to someone and drop some big $$ to get the whole system checked out, I replaced the radiator cap for a few bucks. This solved the problem.

It is very common for the Intake Manifold Gasket to be leaking on these vehicles. This can cause antifreeze to leak out onto the ground or into the engine. Check your plugs, to see if any noticeable signs. Mine is currently leaking bad (99 Tahoe) but is leaking out of the back (by the firewall) and onto the ground. Planning on replacing the gasket this week.

Check the spark plugs for off color. This could be caused by a manifold leak or cracked head, or blown head gasket. These leaks don't always show up with antifreeze in the oil. Another test is to apply pressure at the radiator cap with a leak tester. The tester uses an air pump and a pressure gauge to show how much pressure is being applied. This action dynamicly pressure tests the complete system without running the engine. I've found many leak problems with this test. Best wishes.

Keep in mind, that some leaks can be on and off, and only leak when really cold. Mine only leaks when the truck is cold and when temps are below 20-25 degrees outside. So, when it warms up, it doesn't leak. I had to drive to my buddies shop to do a pressure test, when I get there it wouldn't leak any pressure, due to it being warm. I need to let it cool and try again.

Thanks everyone. After pressurizing the radiator I noticed a very slow leak out or the intake gasket. The oil and plugs checked out ok. I had the intake gasket replaced today.

What did that cost you? My shop next store estimates 8 Hrs labor.

What did that cost you? My shop next store estimates 8 Hrs labor.

Mine cost about $450 at a Chevy dealer, but that was like 3-4 years ago. (about 75K mi) Don't procrastinate too long on this though, I still think this was the main cause of the death of my first motor. I believe that a slow leak in the intake that gets into your oil is very hard to detect with Dexcool coolant. Mine always had a cold start knock after that, and eventually a bearing on the lower end got so bad I had no oil pressure and it started hammering... Put a new GM crate motor in at 106K mi.

Leaks on intake manifold are VERY common on this motor. Often leak is located off back edge, then drips down the bellhousing. looks like it dripping out the weep hole. The set-up is like a bad joke. Check other posts here for more details.

The problem is right up there with problems in CSFI injection system.

It is very common for the Intake Manifold Gasket to be leaking on these vehicles. This can cause antifreeze to leak out onto the ground or into the engine. Check your plugs, to see if any noticeable signs. Mine is currently leaking bad (99 Tahoe) but is leaking out of the back (by the firewall) and onto the ground. Planning on replacing the gasket this week.

I have a 99 R engine Tahoe. Just replaced the water pump, thermostat seal and intake seal and now the engine seems to be still eating coolant. There must be another leak somewhere. I haven't seen any direct leaks onto the ground, so it must be slow or dripping along the back. Any other recommendations. $2000 later and very ticked off.

tertiarydog, rest assured it's going some place.

Before replacing things, failure assessment must be done. Replacing thing unnecessarily can create other problems.

Pressure test seems in order. I have not heard this on Tahoe but on another SUV I have, pin hole leaks develop in head gasket and exhaust gas gets into overflow tank.

If water pump is bad, it will leak out the weep hole under the bearing after 50-70K miles. It could also leak on gasket if old gasket is not completely removed.

The intake leak appears to be on 100% of these vehicles usually in the rear dripping down backside of engine onto transmission.

Another common failure is the quick connect of heater hose to the block. There are two types of connectors onto the right side of block. The potted (molded) one is dull metal and rots. There is a shinny one which is better. Don't have p/n's.

I usually do things myself but occasionally give it to a shop (often regretting it). I did that on the intake manifold leak since it's wife's truck and wanted it done quickly. The dealer replaced radiator cap, thermosat, and oil as part of the repair. Good ideas, it was a good job.