Track day #2=Overheating + Code 2?

[R13]

Ok, before anyone slaps my hand, I searched, found, and thoroughly read:tongue::

http://www.nsxprime.com/forums/showthread.php?t=48505&highlight=overheating+track
http://www.nsxprime.com/forums/showthread.php?t=125245&highlight=overheating+track
http://www.nsxprime.com/forums/showthread.php?t=124601&highlight=overheating+track
http://www.nsxprime.com/forums/showthread.php?t=122405&highlight=overheating+track
and
http://www.nsxprime.com/forums/showthread.php?t=35953&highlight=overheating+track&page=1

That said, I didn't see an exact analog for my situation, and I'm frankly not entirely convinced they are related, but I wanted to get opinions none-the-less.

The Car:

Material to the problem:
-1992 NSX w/226,000 miles
-Stock C30A
-Stock milk-jug (recently replaced due to crack in previous stock milk-jug)
-Stock radiator/thermostat/pressure cap
(radiator could be original, as I have no receipt for replacement, thermostat, & pressure cap are new within a couple of years).

Mods (HIGHLY unlikely to be material to the problem)
-ARK cat-back
-baffled oil pan
-Dunlop Direzza Z1
-KW V3
-Dali "type Q" bars
-HP+ pads

The Track / Track Conditions
-Talladega Grand Prix (aka Little Talladega) www.tgprace.com
-I generally drive it in 2nd & third gear, although I discovered that driving it entirely in 3rd is no slower (Stock 5-speed).
-Vmax was ~110 in a couple of places running anti-clockwise. It's not a fast track.

-Dry/Sunny/windy conditions
-Ambient temperatures ranged between 50F & 70F (track temps unknown)

The situation:

In Session #1 (8:30am, pretty cool outside, 20 minute sessions)
-Following a warm-up lap, after 6-7 (~15 min or so) additional hot laps the car threw CEL 2 (Rear O2 sensor circuit).
-Seeing a CEL, I immediately pitted and parked the car while listening for any shenanigans from the engine. I did not check to see if it was in limp mode.

Session #2
-After about the same number of hot laps I again got the CEL.
-Knowing it was just an O2 code, I kept going for a couple of turns.
-At this time, the car began to get a bit hot. The stock water temp gauge would began to creep up fairly quickly.
-The temp gauge dropped back to normal after ~1/2 lap or less of 4th gear cruising ~3-4k RPM.

Session #3 (about noon-ish now, and measurably warmer)
-After clearing the code again and talking to my engineer (aka my dad on the phone ...automotive engineer), I went out again to see if I could run a session in warmer temps without throwing a code.
-I ran the entire session in 3rd gear, got about the same number of laps before the temp started creeping up, but this time NO CEL ?

Other notes
After this I just began running ~7 laps hard and then taking an early cool-down lap to avoid any over-heating condition, but I never saw a CEL again. The car was fine for the ~4 hour drive home as well.

-The kicker for me is that I was at this same track with the same car (on stock-size rubber and stock suspension) back in August when it was 90+ ambient and I had no issues at all unless I came off the track and let it sit for too long before turning it off.

-I'll occasionally catch a whif of coolant when I start the car and back out of the garage, but it leaves no puddle and the coolant level never changes. I understand this may be normal though as a result of the dump-tube location?

-I read in the other threads that a stock car will tend to overheat when pushed hard for a long period of time. While I was able to push harder (and maintain higher average RPM) since I was less held-back by too-small tires than on my previous trip, the percentage increase in overall average engine speed was probably minimal (especially running the whole track in 3rd).

 

[R13]

Sorry for the book above, and I have a few theories, but I'm curious to hear what the more experienced folks have to say about this.

 

[usafdarkhorse]

Do you run the heat when you track?

Heater core leak causing air bubbles in your system?

 

[R13]

Do you run the heat when you track?

Heater core leak causing air bubbles in your system?

No, that's the MR2 .

I was not running the heat (I had the CC completely off in all sessions). It doesn't have any of the other symptoms of a leaky heater core either (smelling it inside the car, but not out, incessantly hazy windshield, damp passenger carpet).

It's possible there could bubbles in the coolant system, but having dealt with that in the other car, this is almost too consistent with the amount of time it takes. I could be wrong about that, but that's why I posted.

 

[usafdarkhorse]

eh I'm not sure.

I hear cracks on the reservoir can be hard to spot. Maybe a hairline crack that's bleeding off your system pressure?

You can only recreate this on the track?

 

[docjohn]

I think you may have two independent issues.I have had plenty of track days with the O2 sensor cel and never had temp issues...I have only had one episode of high temp and it was due to air after a flush....How is you coolent level?

 

[usafdarkhorse]

Did the CEL isolate the O2 sensor to a certain bank of cylinders?

Possible blown headgasket from the coolant chamber to the cylinder causing a fouling of said O2 sensor? Unlikely.

The two problems may not be related at all and fairly simple as "replace O2 sensor, and the NSX just gets warm on the track".

 

[docjohn]

My O2 cels were due to the faulty heater tip in the O2 sensor bolts as i have a 96 ,this happended more in my car because I was running without cats...

 

[usafdarkhorse]

My O2 cels were due to the faulty heater tip in the O2 sensor bolts as i have a 96 ,this happended more in my car because I was running without cats...

Another member on here who's running test pipes also goes through O2 sensors fairly often. Changes them once a year!

 

[R13]

Well, I've got Cats, AND it's a '92 so I have only have O2 sensors up-stream of the cats, so that wouldn't be it.

I noted in my OP that code 2 is the rear bank. It could be wiring, it could just be the fact that it was probably 30 degrees cooler than the last time I drove the car in anger and the ECU is a slow learner. I was of the opinion that it was probably unrelated, but again, just wanted to check.

 

[pgilliam1]

My bet would be a high pressure leak in the cooling system. Since it runs fine unless you stress it at the track, that leads me to believe that it only happens when it gets pushed hard and temps normally rise. I'd have my cooling system pressurized and see if it leaks. It could be as simple as a weak coolant tank cap. I have a fairly stock 1991 and never have any temp issues at the track, even at 90F. Let us know what you find.
Good Luck and Happy Motoring!

 

[R13]

Ok, so I got to mess with this problem again today a little and I think pgilliam1 may get the prize here.

I could not find any leaks at all. There is no puddle, there are no dried coolant stains anywhere near any of the fittings, etc. The car was a little low on coolant, but I have a feeling that was from puking a little out at the track and the exact volume not replaced afterwards. I'll still be monitoring that more closely than normal for a little while.

I duct-taped a coke bottle over the end of the dump tube to catch anything that might come out of there as that's the only place I found any moisture. I went for a short, but spirited drive and then parked it again and went to sniffing around. The only place I could smell coolant strongly was from the still-empty coke bottle. I could hear an odd hissing noise though. I wasn't sure if it was a vacuum line or what. However on a hunch I pressed down on the top of the pressure cap and it stopped (the car was off at this point, and the temp gauge never got above the normal range during the drive).

So I think after all of that, it's probably either a bad pressure cap(surprising as it's fairly new), or some deformation of the sealing surface on the coolant tank. I'll replace the cap tomorrow and inspect the tank and then see what gives.

 

[R13]

Quick update to this.

I've replaced the pressure cap with another, new 16lb cap. This has cured the obvious hissing from the coolant tank.

However, It seems there is still coolant vapor escaping through the dump tube (the end is moist and there will be a drop hanging on after shutting the car off and checking it after a drive), and possibly around the cap area just based on sniffing around (myself not with a device).

The system still seems to hold pressure. I can leave it for days in the garage and opening the cap still elicits a relief hiss. However, I have to believe this is not normal. If the cap/tank assembly is working correctly, in theory there shouldn't be any coolant (even vapor) escaping around the gasket on the pressure cap to escape via the dump tube or cap seal after say, a gentle 7 minute drive from my office to my house...even if there may be bubbles in the system.

I may get see if I can hook up a vacuum device and see if I can do some type of DIY pressure test of at least the tank area.

 

[pgilliam1]

If you still have pressure after several days of non-use then I'd say your system is holding pressure. I'd suspect air in the system at this point. Mark the coolant level on the tank. Use 2 jackstands and jack the rear of the car up about 12 to 14 inches. Run/idle the engine until it reaches normal run temps (about 5 minutes). Lower the car and see if your coolant level dropped at all. If it did then you found your air pocket and it should be fine. Raising the rear of the car makes the air travel back towards the coolant tank.
Happy Motoring!

 

[mystican]

I ve got a feeling of blown headgasket...just my two cents...

 

[CB72]

One of my friends in France had a similar issue: no overheating on the road but after 3 or 4 laps on a track the temperature goes sky high...
We discovered that there was air in the system.
The bleeding procedure is well described in the NSX factory manual and should be followed religiously as there are no less than 4 bleeding outlets ...
It takes 2 persons to do it correctly.
Hope this helps?
John

 

[R13]

If you still have pressure after several days of non-use then I'd say your system is holding pressure. I'd suspect air in the system at this point. Mark the coolant level on the tank. Use 2 jackstands and jack the rear of the car up about 12 to 14 inches. Run/idle the engine until it reaches normal run temps (about 5 minutes). Lower the car and see if your coolant level dropped at all. If it did then you found your air pocket and it should be fine. Raising the rear of the car makes the air travel back towards the coolant tank.
Happy Motoring!

the pressure cap should be half-off for this correct?

I ve got a feeling of blown headgasket...just my two cents...

Nope (or at least highly unlikely). No coolant in oil or exhaust in coolant. No white smoke. Car cools back down after about 10-15 seconds of reduced throttle, Once it's hot and get's parked it doesn't overheat again any quicker than before. Also, the coolant smell/dump tube weep isn't just during/after WOT runs. I could back the car out of the garage and get the same thing

(hence why I'm still going to pressure test the bottle)

One of my friends in France had a similar issue: no overheating on the road but after 3 or 4 laps on a track the temperature goes sky high...
We discovered that there was air in the system.
The bleeding procedure is well described in the NSX factory manual and should be followed religiously as there are no less than 4 bleeding outlets ...
It takes 2 persons to do it correctly.
Hope this helps?
John

If the "burp" method (described by pgilliam) doesn't get it this will be my next step.

 

[EdinKali]

Or get yourself one of these.

http://www.joetoolcompany.com/mitmv4535.html

You can test for leaks with it and change coolant without leaving air pockets since it uses vacuum.

 

[R13]

Or get yourself one of these.

http://www.joetoolcompany.com/mitmv4535.html

You can test for leaks with it and change coolant without leaving air pockets since it uses vacuum.

Yeah, honestly, if I'd known about these things I would have had one years ago. I own two mid-engined cars and I have a compressor, I see no down-side to this. :smile:

 

[EdinKali]

I bought one when I got the NSX. Works like a champ. I use it on all my cars now.

 

[R13]

Another update:

Burped the system. Got some air out, so that's good. However....I'm trying to track down specifically why I continue to smell coolant around the pressure cap/dump tube area. The car never overheats on the street, and prior to cracking the original coolant tank I never had this issue.

I replaced the coolant tank with a used tank in a pinch so I could make an event. It does not leak coolant (leaves no puddle, water spots on the hoses underneath the tank, etc.).

There are only three causes I can think of for coolant vapor escaping the tank:

-The cap is bad: Ruled out after changing caps, still smelling coolant, and then swapping on a known-good 1.5bar TRD cap from my MR2....and still smelling coolant.

-A head gasket is blown, pushing exhaust gases into the coolant system and over-pressurising it: This was highly unlikely, but I tested the coolant for exhaust gasses anyway.

I used a chemical tester from NAPA. The test is conducted with the car warm and running at idle. Essentially, if the blue fluid turns yellow after sniffing air in the coolant bottle, you have a problem. Here are the results:

From the NSX (original color of test fluid in bottle on the right):
<a href="http://s299.photobucket.com/albums/mm308/3zero/Repairs/?action=view&current=DSC_0525.jpg" target="_blank"><img src="http://i299.photobucket.com/albums/mm308/3zero/Repairs/DSC_0525.jpg" border="0" alt="Photobucket"></a>

From my MR2 (just recently had the HG replaced and the block & heads decked...i.e. it's NOT leaking):
<a href="http://s299.photobucket.com/albums/mm308/3zero/Repairs/?action=view&current=DSC_0528.jpg" target="_blank"><img src="http://i299.photobucket.com/albums/mm308/3zero/Repairs/DSC_0528.jpg" border="0" alt="Photobucket"></a>

What a positive result looks like (Held the sniffer next to the tailpipe for one squeeze of the suction bulb):
<a href="http://s299.photobucket.com/albums/mm308/3zero/Repairs/?action=view&current=DSC_0529.jpg" target="_blank"><img src="http://i299.photobucket.com/albums/mm308/3zero/Repairs/DSC_0529.jpg" border="0" alt="Photobucket"></a>

So I'm reasonably sure it's not a HG. Others have pointed out that a HG flaw may not manifest itself at low RPM, however since I can smell the coolant after basically a sub 3krpm drive around the block...I feel this is a valid test.

 

[R13]

My 3rd and last theory is that there is a flaw in this coolant tank around the pressure cap/filler neck that will hold a vacuum applied to the tank, but not outward pressure. (pulling a vacuum could, in theory pull a hair-line crack shut as it's basically squeezing the tank). A flaw high up on the tank would also explain why it doesn't leak visibly.

I will probably look into an aftermarket metal coolant tank at this point and see where that gets me.


Let me know if anyone sees any holes in this theory....I hate invisible leaks.

 

[LJSB]

Sticking thermostat, not opening all the way.

 

[R13]

Sticking thermostat, not opening all the way.

The overheating part or the coolant smell? I could understand for the overheating, but I'd expect symptoms far sooner than 15 minutes into a session if flow to the radiator was somehow restricted.

I took the car to an autocross over the weekend (won my class) and it never got hot (short runs, so I wouldn't have expected it to) and no coolant loss. However, the audible hiss from the dump tube/pressure cap area re-surfaced. If I push down on the forward "ear" of the cap, it stops, if I press on the rearward ear or if I just let it sit, it starts again. This led me to believe that there is some deformation with the brass-looking collar and/or the latching mechanism on that assembly. It's either not holding the cap down tight enough or it's deformed to where the cap does not seat evenly.

I'll be replacing the tank with a metal offering (which I had planned to do anyway at some point), and then thoroughly bleeding the system in the coming week or so.

 

[EdinKali]

If you plan to replace it anyway you might want to give this a try before you do.

Use a sharpie to color the tank neck sealing surface. Then take a sanding block with fine sandpaper(start with something like 400 grit, you may want to finish with 600 or 800 grit) and carefully sand the neck surface. Any low or high areas will show up as you sand off the sharpie marker. Once the surface is perfectly flat, give it another try.