GSGALLANT

Let's not forget about the fact that the cap is designed to maintain a certain pressure in your system. It doesn't matter whether the source of pressure is coolant heating up and expanding in volume, or combustion gas pressure coming into the system throught a head gasket leak.

Now, that being said, if you have a HG leak, the leak rate may be higher than what your cap can relieve. So, to test that, I would get your truck nice and hot (after a long drive on the highway) so that your hoses are rock hard, then shut the truck off. Over time (I'm only talking 4 or 5 minutes here... enough time for your cap to bleed off any excess pressure and return the system pressure to normal, but not enough time for your engine to cool off), what happens to the pressure in the system (do the hoses get any softer?)

If they don't, then that is the pressure that your cap is controlling it at (since your truck is shut off, the possible source of pressure from combustion gasses is gone, so your cap should bring the pressure back down to it's rating within a few minutes.)

MustangMike

thanks for all of the replies, guys!! I just finished the leak down test - NO LUCK!!! The lowest number of any of the cylinders was 87.5 (aka 12.5% leakdown in that cylinder). All other cylinders were 90 or above, I actually had 98% in the number one cylinder! I'm in shock that the numbers are so high for as old as the thing is with as many hard miles as it has. Would you agree that those numbers are decent? From everything I've read, they are well within a good range.

So that doesn't solve any problems. I did some more investigation. My mom has an '06 runner, so I checked hers out. Warmed it up, took it for a 6 mile ride with the ac on and romping on it every chance i got. Pulled it in and the lower rad hose is actually cooler than mine is. AND, get this, the pressure in the hoses is VERY similar to mine, though mine feel a bit harder - but not much. MTL you were right - needed to look at other 4runners to see. Granted it's an '06 and I have a '97, but it makes me feel a bit better.

I would hate to see all of this be over a bad hose clamp on the upper rad hose, so I think I'm going to change that tonight (where the leak is) and drive it a good bit and see what happens (I'm out of ideas at this point). If it continues to leak, I have no idea what to do. If it doesn't leak, well, I'm gonna feel like a major idiot!!!

Thanks again for all of your help - I hope this thing is solved. I'll let you know.

Mike

GSGALLANT

With respect to the lower rad hose being cool, remember that the radiator's only real job is to lower the temperature of your coolant. Hot coolant goes in at the top, and its temp gets dropped before it exits at the bottom. I'd be worried if your lower hose was not cool.

ZUK

iTrader: (1)

Mike- Just curious....did you replace all those things mentioned above because it was over-heating?

edit-never mind. I searched and found your other overheating post. Still sounds like a head gasket blew on you.

edit- so when it's cold......and you take the cap off and start it and let it come up to temp.......do you see the water flowing past....or does it bulge up and start massive over-flowing?