2 1/2 gallons lost??? That is a lot of coolant.

The heater thing could be a clogged core, not unusual unless it worked yesterday and not today.

You COULD be losing coolant through the port(s). This wont show up as white smoke either since it isn't being burned in the cylinder. Are your heads ported or ever have any serious over heat issues? A coolant leak down test will help. Be sure and do one cold AND hot. With thermal contraction and expansion, a slight leak might not show up cold but will when hot. If you are leaking into the exhaust chamber (AFTER the cylinder, you MIGHT see water droplets coming out of the exhaust if the leak is bad enough. I found mine by removing the exhaust and running straight headers.

Either way, enjoy the cruise, life is short......

 

OK so bad news. New cap and thermostat and it's still doing the same thing. Will idle fine in the driveway at about 210 (160 thermostat though so it usually idles at 170-180 even on a hot day) but drive it a block and it creeps right up to 240+. So one trip around the block and it was too hot to drive any farther.

Still also no sign of where the water is going though. I guess I'll have to learn how to do a coolant leakdown test.

Heads are stock and original as far as I know. I've had the car 5 years or so and the previous owner didn't mention any head work.

The only time it has overheated at all was the other day when all this started. The temp gage went up to 280, then dropped to 0, and the temp sensor was bad so I thought it was just being flaky. We were almost home when that happened so I only drove it like 3 blocks at 280 and shut it down to let it cool completely off before I messed with it. Then again yesterday I shut it off before it hit 280 and had it towed home. So I can't rule out a cracked head due to heat but it seems unlikely.

Tonight after the cruise (guess we're going in the van ... I'll check again to see if it's leaking coolant or for any signs of coolant in the oil or vice versa. No moisture at all out the tail pipes. No smoke no noise still...

Still no 'hope' it's the water pump? Also original as far as I know.

 

You can leave the cap off (starting with a cool engine) and after the thermostat opens, you can look in the neck to see if there is coolant flow. You should really get (rent or whatever) a pressure tester, so you can track this down.

2-1/2 gallons is over half the system capacity. It's going somewhere.

 

Shoebox is right. If the cooling system will not hold a steady pressure(applied via the pressure tester) for a few minutes, then you have a leak.

If you have had it to 260*(I assume you meant 260 instead of 280), you'll be lucky not to have warped the heads. My cooling fan fuse blew and while I was trying to track down the air pump code it threw...I let it overheat...pegged the temperature sensor past 260*(didn't have any idea the cooling fans were on that fuse)....was looking at the computer scanning with autotap when I smelled coolant....I knew a fuse was blown at that point. The car temp acted erratic after that....going up and down while steady state cruising. Turned out that just one overheating warped both my heads 3-4 thousands causing problems.

Now I may have gone wrong by slamming in a new fuse and cooling the engine down quickly. If I had let it cool slower...I'm not sure I would have had warped heads....but the moral of the story is don't let the engine get near the red zone.

 

Well you guys are just full of good news!!!

Yeah I think I'm in denial. It may have gone over 260 the other day, the gage stopped working. The idiot light came on just as we turned off Polo Road so I drove it the last 3 blocks home with the gage in the red, but before we got to the drive, the gage died completely (went back to 0) so I thought maybe it was just flaking out. But it may have been really hot, I don't know. I shut it down in the drive and let it sit til morning.

The entire 1.5 mile test drive today it puked out the overflow tank. I'm wondering now if it's pumping compression into the cooling system? So then it pukes out the overflow tank and that's where the coolant is going without getting in the oil?

Bad deal either way. Will do the pressure test thing and report back.

 

Maybe this would be a good time to find an LS1 car wreck and swap over to the dark side?

 

As shoebox said above...Have you verified that the coolant is actually flowing? Even warped heads do not generally stop the heater from putting out some heat when there is coolant in the system still.

 

Oh yeah, sorry! Yes it certainly looks like coolant is flowing. So I'm assuming if it's flowing at all, it's flowing well enough?

Also, another WTF issue here is that after the day it overheated and I'm not sure how hot it got, it ran fine (and 180 degrees consistently) in the current summer heat and traffic for about 24 hours. Then all of a sudden overheated again.

So, if that one time did crack or warp a head, would it have run cool for 24 hours before it started overheating again from that damage?

 

I agree..does not make sense that it would run cool after it had overheated and have a delayed head warpage and or headgasket failure that long after the fact. Just a crazy thought...is it possible that you have a hose that is collapsing in on itself on the intake side of the waterpump that prevents the pump from picking up the water for circulation? Just a wild shot in the dark..but food for thought anyway.

 

Another thought. Maybe the collar that connects the water pump to the pump shaft on the engine has broken or is partially stripped and not allowing the engine to turn the pump at required speeds... I know it is another far fetched idea..but more to consider anyway.

 

I kinda wondered that too? I had the pump off last fall, to put on a new opti. It seemed in good condition, I put new o-rings on it and greased the shaft. But it's a possibility. Original pump too with 125,000 on it. Didn't have the money for a new one when I put on the opti. Or now for that matter.

Would it help if I video record it from a cold startup, so that you can all see the flow inside the radiator neck, the temp rise, and the overflow tank spilling over? I might have to 'time elapse' it as it might take 10 minutes to get up to the point of overheating, but it would give you a much better idea of how it all plays out than me just trying to explain it?

 

I think a video would be of some assistance in helping us diagnose the possibilities. Hang in there...all will workout in the end,

 

Rent a cooling system pressure tester from Autozone, fill up the system, and put the pressure tester on the radiator. Fire up the engine and pump the pressure tester to 5-10 psi. Does the needle vibrate? If so, you may have a head gasket leak(compression is vibrating the needle).

Look at the beginning of this video. This is what the needle should look like...steady. Until you rev it and then the needle should follow the pressure applied by the water pump.

http://www.ace1252.com/images/CC503_...ant_tester.WMV

The pressure tester can really help reveal an external leak on a cold engine. It help with internal leaks too, but you want to be careful. If you have a head gasket problem and it's leaking into a cylinder, you don't want to risk hydro locking a cylinder.

 

OK so here's the video...

http://www.youtube.com/watch?v=QAmtaNsADy4

 

Holy high tech videos!!! And you and I have the same battery!

I'll get one this week and begin diagnosing... :sigh: