Your thermostat is stuck closed. Thats why you have a leak at the water pump ( it's pumping and it has no where to go, so it goes out the gasket). Also explains why your overflow fills up after turning off the engine ( all the pressure is in the engine and non in the radiator, when the engine turns off, it back flows past the water pump thru the rad and into your overflow tank to even the pressure). I recomend replacing the thermostat with a safety valve type thermostat ( the ones that fail open, they cost a little more than the regular thermostats but you'll have peace of mind knowing there is flow regardles). Also flush the coolant system ( to get rid of any possibility that there is that orange sludge from a possible mixture of Dexcool and regular antifreeze). Thats it. All the best.

 

I'm not familiar with the opti, but on the HEI there is a large pink (red) wire that goes to a connection on the distributor cap marked "Bat" (battery). Disconnecting that disables an HEI. Check the wiring schematic in your FSM, to be sure.

RACE ON!!!

 

So you are saying that all his problems, including the leaking water pump, and the blowing of the coolant into the overflow reservoir, are normal for any engine before it warms up enough to open the thermostat?

RACE ON!!!

 

Yeah, I don't know about that. I know my cooling system pretty well and this doesn't make any sense to me.

Can someone tell me for sure how to disable my ignition system on an LT1/LT4? Would pulling both ignition fuses do the trick? I'm sure it would, I'm just not sure if there's some special reason for disabling the ignition that I'm not seeing that this wouldn't address.

 

To disable ignition, pull 10A fuse 25 marked "coil" in the IP fuse panel. The chart is on the inside of the fuse panel door.

 

Thanks! On my way to compression test now.

 

Firing a coil that has no path to discharge is not a good idea. Can cause arcing in the distributor among other things.

 

Makes sense now. Thanks!

 

This is an awesome post that should be quoted EVERYTIME a thermostat thread comes up.
He is right and that's why I run a 160, my stat opens faster thus not wrecking gaskets and causing the puke tank to overfill.
Can I hire you for a technical assistant?

 

An LT1 thermostat is never closed and water continuously circulates through the water pump.

All LT1 engines utilize a special 2-way acting full bypass thermostat. Dual-acting means that the thermostat regulates coolant flow both in to as well as out of the engine, while the bypass portion of the thermostat circuit supplies the water pump with a full flow of liquid coolant at all times. This is unlike a conventional engine thermostat, which only regulates coolant flow at the engine outlet, and which does not allow full flow through the water pump when the engine is cold and the thermostat is in bypass mode.


Both sides of the 2-way thermostat used in the LT1 are linked together, and a single wax pellet actuator operates the spring loaded mechanism at a pre-set temperature. When the designated temperature is reached, the wax pellet expands, opening the dual acting valve

The LT1 is completely different since it uses reverse flow cooling. The incoming coolant first encounters the thermostat, which now acts both on the inlet and outlet sides of the system. Depending on the engine coolant temperature, cold coolant from the radiator is carefully metered into the engine. This allows a more controlled amount of cold coolant to enter, which immediately mixes with the bypass coolant already flowing. This virtually eliminates the thermal shock present in the old system.

After entering through one side of the 2-way thermostat (at the appropriate temperature), the cold coolant is routed directly to the cylinder heads first, where the combustion chambers, spark plugs and exhaust ports are cooled. Then the heated coolant returns to the engine block and circulates around the cylinder barrels. The hot coolant from the block re-enters the water pump, and hits the other side of the 2-way thermostat, where it is either re-circulated back through the engine or directed to the radiator, depending on temperature.

All of this means that the thermostat housing is the INLET (opposite of most engines), while the water pump is the OUTLET.


There are three main circulation systems for the LT1, while most engines only have two systems. As with most cars there is circulation through the heater core and the radiator, but there is a third system on the LT1 which includes steam vents in the head, along with a pressurized reservoir.


Most of this is borrowed from an article by Scott Mueller.

 

Sure! As long as you live in Toronto Canada!

 

Thanks for clearing that up. Still, I think that there is some kind of blockage somewhere and it wouldn't hurt to start fixing the coolant problem by replacing this special thermostat. Or, if you read the rest of my post, flush the entire system ( to get rid of the possible Dexcool/green coolant sludge ). If flushing the system doesn't work i'd take the heads off and check the coolant passages and also might as well check the head gaskets while your at it.

P.S. Also check the rad and make sure its not chocked up with sludge.

 

And reuse them if they weren't blown???

RACE ON!!!

 

Okay guys, I did the compression test. The results aren't too bad. Exactly 200 PSI in all cylinders, except for the rear passenger cylinder which read 185 PSI. That one is only off by 7.5%, so maybe my headgasket is ok. Could it be that the coolant all ended up in the overflow tank just because I maybe broke the cooling system's vacuum somehow playing around in the engine bay, and not because of a big deal like a broken headgasket?

 

Oh and by the way those compression readings were with the engine not at operating temperature and the rings were probably not wet with oil, so that means those numbers are pretty good right?

What can I do to further assure I don't have a blown head gasket? A leak-down test? CFI-EFI, is that the same thing as a cylinder leakage test?

 

A cylinder leakage test is different, but it won't tell you any more about your head gasket than the compression test. Something seems wrong with those test results. Seven cylinders exactly the same and one, that is that much lower, while within range, just looks "funny" to me. Did you have any help? Any supervision? Your symptoms so strongly suggest a blown gasket, I think I'd do it again.

The only other GOOD test I can think of is the CO in the coolant test, but that requires running the engine.

RACE ON!!!

 

Yeah I know it was kind of weird, all 7 of the ones that read 200 were pretty much right on the mark with no discernible variation between them whatsoever, and then that #8 cylinder just couldn't quite make it that far no matter how many times I cranked it.

I'm pretty sure I did the procedure right; I pulled the COIL fuse, and with all 8 plugs out I tested one at a time, with my stepdad holding my throttle wide open manually while I cranked the car. Letting the cranking noise cycle four times is what it took to make the reading level off for each plug. I guess it would be worthwhile to test the #8 cylinder again, and make sure the hose tightness and any other variables weren't an issue, but I live 30 miles away from my car so that will have to wait. Plus I'm going to kill my battery if I keep doing this. But I'm pretty sure about those results.

 

Hippy and CFI dead on right, listen to him. Your exact same symptoms happened to me.

..after it was shut off, would over flow..Sometimes the lower hose would blow off. Lost water from teh fill level only.

...Water pump started seeping

...No water visible in oil

...Ran fine, occasional slight miss at idle. Only seldom got hot-Mine was temp sensitive. Even passed smog with it like that.

Radiator pressure test came out good. Know why?

I say its time to tear it down .

 

You might be right but there is just not enough evidence yet to convince me that I need to go to that massive trouble. I've had enough of "tearing the car down" this year, and I will not do another minute of it (much less the weeks it will take me to actually learn to get the engine apart) without being sure that I need to. This is happening immediately after I had finished all my work on the car, fixed every single driveability issue and leak and clog and what have you. I wasted the whole summer on this and now it's time to go back to school. I'm not in the mood to just go hog wild "tearing it down" again after months and months of frustrating work, until the tests confirm that it really needs it.

 

One test that I like is what I call a "Poor man's leak down test". Poor, because I'm not using the proper (expensive) tools to do it w/the gauges.

I take my compression tester, which has a gauge, and a set of hoses for various applications. On the end of each hose, I have a quick connect, like a shop air hose. Does you compression tester have these features? IF so, you can use a valve core tool to remove the schreder valve in the hose that fits your engine. Turn the engine to get it at TDC firing on number 8 since that's the cylinder in question, then pressurize the cylinder w/as much air pressure as you can w/o turning the engine. 30 PSI is plenty for this test. Remove the radiator cap and look for bubbles. If you see them, it's a head gasket (most likely) or a cracked head or block.

FYI if you don't get bubbles in the coolant, you can listen for air "noise" at the oil fill cap, tail pipe, and throttle body to diagnose your leakage as rings, exhaust valve, or intake valve, respectively.

-Tom