The Mountain Kat

Hi guys,
My trouble started over a year ago and I'll start the description before that. The overheating is worse in traffic but I cannot drive on the highway in 4th as she'll heat up. I can't run the A/C. Period...
I installed an A&A Vortech V-2 Si trim setup, Long tubes, Patriot Stage IV 243 heads, a mild SC cam, and LS6 intake, a 160° and some other minor frills.
Everything was great. Never a problem.
I changed the heads out for a set of RHS 54225 Pro-Elites. Some minor fitment problems but no big deal. I also made a 3/8" tunnel plate and covered both sides with a thermal barrier material that is about 5/16" thick.
I drove her around for about a 1000 miles and the power increase was amazing! But I noticed the heat coming off of the tunnel had *increased* rather than decreased. Odd to my thinking but I didn't have time to pull the plate and barrier out.
I took my son and we drove from Tucson to San Diego for a week. This was in July.
She ran beautifully. Then we started home and halfway between Yuma and the I-10, I noticed the A/C warming up. Checked the temp and it was at 215° so I turned off the A/C and she took some 10-15 miles to cool down to 180°. I had been behind a grain truck that was losing lots of chaff so I figured that the vacuum cleaner effect had clogged the radiator.
The next morning I lifted her up and found no problem with the radiator.
Having had several thermostats seize closed I bought a new one and pulled the SC to get at the thermostat. I suspended the thermostat into a pot of water and cranked on the heat. No problem it began opening at the right temperature. But just to be sure I put in the new one anyways.
Still getting hot. I can't drive 5 miles in traffic before she is running some 230°. I turn on the heater to full and it'll pull 20+ degrees out fairly quickly. So I figure an airflow problem.
I replace the fan assembly, went to a nice big aluminum radiator, and new coolant.
Still the exact same overheating.
Pressure loss in the cooling system? Nope a block check and pressure test shows to exhaust leak into the system nor pressure leak out of the system.
I have pulled the heads to check the gaskets and whether the heads warped. I ran a check for a cracked cylinder while the heads were off.
Maybe the water pump? Nope a brand new pump and no change. Collapsed hoses? Nope. Hose separated inside and forming a blockage? Rare but I have seen it so I checked those.
I pulled the A/C condenser out and drove for a couple of weeks. No improvement. I flushed the system and replaced the coolant with water. Nope.
Is it possible that these C5s are so dependent upon undercarriage airflow that the Thermal barrier inside the tunnel could restrict airflow? Doesn't appear to be. I didn't pull the exhaust and plate but I got a pretty good look up there using a mirror.
Nothing that I can think of is the problem.
What am I missing here?

Corvette_Ed

215-230 are within normal operating temperatures, especially in July in Arizona. You could try cutting a hole in the bumper behind the license plate cover and going with a cover that has a screen in it instead of the stock one to introduce more outside air to the radiator.

One thing you might check, though, is the fan operation. When you turn the A/C on the fans are supposed to come on, even at highway speeds, which should lower your temps, not raise them.

dmarkshark

You've done a lot. Can we assume that you burped the system after the coolant changes, and not just filled it up?

The Mountain Kat

Oops I forgot to mention that the fans do come on and I did burp the system. I have a small hill in my yard that I pulled her up on just to be sure that any air would have an easier time moving towards the reservoir.
I reset the fans operation using Hptuners and this didn't help either.

3boystoys

I see no problem.

Corvette_Ed

In that case about the only thing you can do is to try and bring more outside air into the engine compartment. The screen license plate cover mod is a good way to do that. Everything on your car is operating at normal tolerances, so there really isn't anything to fix.

The Mountain Kat

Something else that I forgot was the grill opening mod.
Things are within *operating* range but she was running at 180° +/-5° with the A/C on and now she is running at 230° plus and I cannot run the A/C. There has got to be a problem that I have overlooked somewhere.
She was running about 180° in 115° outside temps until something happened while driving back from San Diego.
Now she runs 230° even in 70° air after just 3 or 4 miles. I'm afraid that if I drive anywhere farther that she'll get even hotter and hurt something seriously.

Corvette_Ed

I don't have a link to the thread, but there is a thread here in the Tech section about loosening one of the coolant lines from the head. It's possible that you have some air trapped in the system that the normal burping procedure is not getting out. Try doing a search for the thread and see if that fix solves your problem. It's about the only thing you haven't tried yet.

The Mountain Kat

Ah. I replaced the sensor too.
And when I put on the new waterpump I found out the hard way that the surface that runs from the center area of the turbine to the heater house outlet is about 1/4" higher. Which restricted the idler pulley from turning and caused the serpentine belt to eat the pulley depositing the melted plastic onto the upper idler pulley. I just pulled things apart and the lower pulley is gone. Nothing but the bearings are left. One of which is destroyed. The cage is broken and a couple of the ballbearings are missing...
So I ordered a couple of new idler pulleys and a belt which should be here by Friday.
Sigh...

Medic!

Air moving across the engine. And over the bell housing. But not out the tunnel?

How dose the hot air evacuate the engine compartment if you dammed up the tunnel for the torque tube? Would it not just pool in the engine compartment?

pewter99

FWIW it took opening the front up to get my Maggie C5 to run cool with the AC

linz5

just curious. . . .is your "air dam" (the one that catches all the road kill) still in place and functioning?

kabluie

You may consider using one of those hoods that expel and increase air flow past the engine. You can check that by leaving your hood ajar and go for a short distance to see if that helps. Are you pulling any codes? You may want to get an OBII analyzer which will tell you why any codes are happening.

Good luck with it.

The Mountain Kat

Hi guys,
Just got back on. More problems but I'll start a new thread for that.
I opened up the front and made a nice ZO6 style screened setup for it. Not much change.
The air-dam is in place. The tunnel airflow is my last analysis. I looked as well as a small mirror and flashlight would let me. It *looks* like the thermal barrier is in place and not bunched up causing blockage BUT that is while standing still. I can get my hand in there enough that, by feel, the 5/16" thick stuff is still attached as well as when I installed it.
It will be a PITA to pull it back out but that is my next step. I can pull the material back off, clean the bottom surface, and then apply some of my Techline thermal barrier compound.
It's about the only explanation that might explain why the overheating developed while I was driving. A steady 65MPH and in the course of about 20 miles it went from 180°+/- with A/C to 220+ without A/C.
I also checked all the relays for the fans and forgot to mention that. Both fans work fine.

Ray 2000 C5 FRC

What is the age and type of catalytic converter does the car have on it now. If your engine temperature returns to normal at idle or low speeds and overheats during highway speeds, your converters could be toast and need replacing. Check your DIC to see if your O2 sensors are working properly, I seen many people ignore O2 sensors warnings and it results in frying the catalytic converters.

ONE BMF

Try my front bumper mod-This it can't hurt and helps greatly with cooling https://www.corvetteforum.com/forums...cover-mod.html

65GGvert

Forget the fans, they don't run at speeds over 35mph with or without a/c on.

Corvette_Ed

This isn't my understanding from what I've read here. If the A/C is turned on at speeds over 35, I've read many times here that it turns on the fans.

65GGvert

Turning on the a/c forces the fans on at lower temp (185) at speeds under 35mph. They still turn off over 35. That's with a stock tune, I don't know what the OP has done with the SC and other mods.

The Mountain Kat

I think that I have been over anything and everything that could possibly relate to this overheating. Desperation made me do things that I was sure couldn't have caused it.
The CATS are definitely not the problem. So I spent most of my Sunday under the car dropping the X-pipe and removing the thermal barrier form both side of the tunnel plate.
I have some pretty serious doubts about that airflow being that critical but exasperation has me doing that.
If the problem *is* the tunnel airflow then why didn't it manifest itself during the 1000+ miles driving in traffic during Tucson's nice hot summer before my drive to San Diego and back?
One thing that occurred to me while under there are the rear O2 simulators. I removed the post CAT sensors and used those dandy little black boxes as well as shutting the sensors off in my calibration.