My '99 is doing something weird with its antifreeze. Lately it has started to require about a gallon of coolant for each week or two that I daily drive it. No visible leaks from the engine (though I haven't done a really thorough investigation), there are no drip leaks at idle (when it loses coolant the fastest), the exhaust doesn't smell like antifreeze, and there's no indication of engine oil in the coolant or vice versa.

That being said, I just checked the external reservoir the other day and noticed that it was completely full of coolant (despite there being air in the radiator). so I dumped the extra back into the radiator and cleaned the top of the bottle. The next time I drove, the reservoir was again almost completely full of coolant both right after I had driven and after several hours of letting the engine cool. Again there was air in the radiator, and this time there was evidence of coolant leaking out the top of the reservoir bottle.

Does anybody have any ideas as to how the reservoir is becoming filled to the brim with coolant and air is getting into the radiator?

 

Start simple

Fill/bleed the system, and check your cap.

 

I'm having the exact same issue except, today the temp guage went to "H". I went home and bled the system but now my rpm shoots up to about 2k

 

So, after doing some more testing, getting an OEM cap and that still not solving the problem, I rented a combustion leak detector from autozone. after running a couple controls on a known good car, I tested my RL and yep, I am getting combustion gas in my coolant. a compression test revealed that the #3 cylinder is maybe 10% lower compression than the rest. not a huge difference but it's all I've got to go with.

since my wife and I have 3 cars total, I can afford to let the RL sit for a couple weeks while I take my time...

...replacing the head gaskets...

...and hoping the culprit isn't a cracked block.

While I have everything apart I'll be cleaning external parts to make the engine bay look like it doesn't have 240K on it, giving all the lifters a thorough cleaning, checking valve seats/seals, and having another look at the EGR system (though i just cleaned it a year and a half ago). might replace the O2 sensors while I have the exhaust manifolds off too.

I've worked on it a couple evenings this week and I've got everything up to the intake manifold removed.

so far this job hasn't proved to be too difficult, with no special tools required besides the basic wrenches, sockets, pliers, a rubber mallet, and some PB blaster. we'll see how that changes.

 

If your going to have the whole engine apart basicly, and if you have a couple of extra dollars I would suggest changing anything that's rubber. Valve seals intake manifold seals and cleaning etc. Basically a whole top end set. Anything that wont be easy to swap out unless uninstalled again.

 

I did get a whole top end gasket kit and I do plan on replacing everything in it.

 

sounds good.

Don't forget about vacuum hoses or anything else rubber or brittle.

 

This is just an aesthetics thing but you ought to totally clean the engine bay while you're in there! Get all the grease off and make it look brand new!