This is in regard to a '96 CE with LT4 and ZF6...

Which setting is more accurate...what the analog gauge says, or what the digital mode says?

I just did a pretty extensive cooling sysytem overhaul, including a new radiator...and while idling checking for leaks, the analog gauge is almost pinned...just below at maybe 250...while the analog is way less. I turned the car off once it hit 230 on the digital. Just didn't want it to get any hotter. Almost like the thermostat isn't opening, but I put a new one in and checked it first. Makes a lot of heavy sucking sounds and clicks when I shut it off...normal? How hot should I let it get?

Thanks!

 

Digital is always more accurate. The analog is really a "cold", "medium" and "HOT" light bulb with a needle stuck on it.

Fans don't turn on until somewhere around 230F.

 

Yea, the analog shot up to the 250ish range real fast, and just kinda sits there...while the digital one goes up slowly. I got the fans to come on by turning on the AC, but it still keeps going up. I would expect it to start going down once the thermostat opened. Both hoses are hot...shut it off at 230. Do I need to let it get hotter?

I tell ya, I always like the digital gauges like the ones in my '86...too bad they are so problematic.

Thanks for the reply!

 

how much fluid did you get into the system? If you didnt get damn near 4 gallons in, you have a massive air bubble somewhere.

 

^^^ Not if he didn't drain the block. I saw that he changed the radiator. That should be about 2 gallons or so. If he DID drain both sides of the block, then I agree...4 gallons.


No you don't need to get it hotter. Once cooled re-check your coolant level. Did you open the bleeder screws when you re-filled?

With the AC on, fans running, the cooling system should be able to drive the coolant temps down below 200*F. Either you have air in your system, or the radiator has got debris in front of it, IMO.

.

 

Hard to judge. I was filling it when I discovered a radiator leak. Lost some from that...got the rest of the 4 gallons in there. Looks to need some more now that it has cooled down some. No "Low coolant" light. Thanks!

 

I did drain the block too. I did open the bleeder when I first filled it. It over-spilled and lost some...how do I avoid that? When I filled it now after the new radiator, I decided to leave the cap on, and the bleeder closed. Figured I could top off after it cooled. Hate that stuff spilling everywhere, and at $19 a gallon. New to this reverse cooling thing. Listening to any advice you may have...thanks!

 

I have a L98, not a LT1 but here's what I did when I was working on mine. I filled the radiator to the top with the engine off and cold. I took a jug and cut the bottom off and put it in the neck of the radiator and duct taped it to the neck of the radiator acting as a funnel. I also turn on the heater to the highest setting so coolant runs through the heater core too. Start the car and let it warm up so the thermostat opens. When it opens, the coolant will rise into the funnel a little then drop. Top the radiator off while still running and put the radiator cap on plus top off the overflow tank. Ran the car a few blocks then checked the tank later.

It worked for me.

 

L98...that's a sexy beast! Still gets my vote for best looking engine! Thanks for the tip! Open to hearing whatever, but if nothing else comes up, I'll try that one. Thanks!

 

I just did my 96 from completely empty(knock sensors pulled), new hoses and new thermostat.

The FSM says to fill it, run it for 4 minutes, shut it off, then fill the overflow in the forward passenger corner to the cold mark. At the 4 minute mark my fluid was only in the 130's.... not hot enough IMO.

I got like 3.3 gallon in to full cold(probably 2.5 gallons or so until the bleeder screw bled some fluid). Started the car and ran it until the temps were 190-200(so I knew my 185 thermostat was open) with the cap off and shut it off, capped it, and added fluid to the HOT mark. As the system cools at that point it will draw fluid into the system. About 5-6 hours later(after the car cooled) it had drawn some fluid into the system and I think I ended up halfway between hot and cold.

The 96's do not have a heater valve in the lines so no real NEED to put the heater on full blast like on the older cars.

Car will sit and idle at 198-205 with the AC on(to force the fans on) in 100 degree temps. Went to the auto-x the other day, did 5 runs, car never got over 205.

So IF you dont have a massive air pocket somewhere you have something else going on that is causing your car to get that hot. IF the fans kick on they should pull the temp down fairly quickly.

What brand themostat did you put in? You might have your expansion tank cap checked to make sure its holding the appropriate pressure.

 

Did you use a LT1 thermostat? (as it has reverse coolant flow on a LT1)

Initially after the first time you started it and got it hot and it cooled down, did it draw coolant from the over flow tank (which you should have filled to mark) back into the engine?
It should have pretty much emptied the tank at full cool down.

 

I bought one from an auto parts store, for the year and model...Stant. Is that not correct?

Are you talking about the white tank, or the black one. Black one got sucked dry, but white one may have a little in it...will have to check.

Thanks!

 

$19 a gallon? What are you putting in that car? Have you replaced the radiator cap? Most people don't replace their radiator cap until they do some major changes. It has a lot to do with your cooling systems ability to work properly by maintaining pressure in the cooling loop.

Did you use distilled water with your coolant or did you buy the pre-mix? I have seen way too many people who use pure anti-freeze in their cooling systems and then it overheats. Be sure that you use the proper ratio for your region, I run 30% a/f and 70% distilled water here in Virginia, it does not get as cold here as other parts do.

A bottle or two of "Water Wetter" will help quite a bit on a hot running car. This stuff is not "Snake Oil" like some will tell you, it helps the metal transfer the heat into the coolant. Inside your engine when it gets hot, a layer of steam bubbles form on the hot metal surfaces and this "Water Wetter" is a surfactant which eliminates the bubbles from forming therefore allowing more heat to be extracted. It really works and it has been around for a long time because IT DOES work!

The LT1 engine seems prone to holding air in the engine, you might put the car on ramps while working the air out, that has been mentioned by others as being helpful!

I hope that your car "Cools Down" a bit and you get a handle on this heat issue. You are certainly in the right place to get answers!

 

I actually think quite the opposite. My 96 is the easiest to bleed corvette I have owned. My 2 C6's were a pain in the *** because the expansion tank is not the highest point in the system. The C5 is most likely similar.

The black expansion tank is the highest point in the system. Its very easy for air to get out. If you put the car on ramps, IMO you would risk getting some part of the system HIGHER than the expansion tank/radiator cap and could possibly trap a bubble in the high part.

I personally DONT like the GM procedure as it does not, IMO, get the engine hot enough(not hot enough to open even a 160 degree thermostat let alone a 180 or 195). Their procedure calls for filling the system with as much as it will hold, run the car 4 minutes and add coolant as the level drops, shut the car off, cap it, and fill the over flow to the cold line. If you follow this you will be AT LEAST half a gallon shy of the ~4 gallons the system holds. When I did this the upper radiator hose never got pressurized either. I think the car only got up to like 130-140 degrees in the 4 minutes the prescribe.

I fill the system as full as it will go, ~3.25 gallons, start the car, keep the fluid level up as it goes down,usually another .25 gallons. When it stops taking fluid I let the car come up in temp until I see the fluid start expanding(usually like 185-190) then cap it, shut off the car and add fluid to the overflow until just below the hot line(~.4-.5 gallons). I end up with like .1-.15 gallons left, about 1" or so in a milk jug.

The LT1/4 system self bleeds small bubbles, but if you got a large bubble trapped somewhere, in theory, it should bleed itself, but then your fluid quantity would then be way down. I always check fluid quantity after about 2-3 heat cycles of driving.

 

I totally Super fast and easy. Fill to top. Open bleeder(s) until you get coolant, then close 'em. Top of surge tank, then overflow....put cap on, you're done.

 

When I did cooling system service (1995 LT1), I did pull the knock sensors and flushed all. Then put it all back together and poured as much coolant as possible into the surge tank (black). Then ran the engine until visible coolant flowed through the surge tank, meaning open thermostat. The level dropped so I refilled the surge tank as high as it would go, I mean tip-top full, then put the pressure cap on and shut it down. Then added coolant to the overflow tank (white) to about halfway and it's been fine ever since. T
I understand the system will purge itself of air, although it could not hurt to use the bleeder valve (brass) on the metal elbow near the throttle body.
And it is very important to use the correct thermostat for the reverse-flow cooling system -- stock thermostat is 180F.