Still overheating

[NSX-Racer]

Okay, Larry & Co., you may chime in here: After changing the head gaskets due to overheating at the track the car still overheats after a few hot laps - water temp gauge goes into red (I experience less power) and after a short time the engine control reduces max rpm and I get a check engine light (code 22) which disappears after restarting. Ambient temp was in the normal middle european range - nothing extraordinary.

As soon as I began to shift at about 6000 rpm instead of 8000 the water temp came down after one or two laps to the middle of the range.

The coolant system seems to be fine (bleeded several times), we removed the thermostate in the engine bay to maintain the water flow over the whole time, we bridged the fan control at the radiator to let it run the whole time.

What can be done next? Has the ignition timing adjuster in the engine bay any influence on the engine heat (ignition too late or too early)? Is it a hint that I see some white smoke out of one exhaust pipe when I start the car in the morning but no smoke out of the other pipe (exhaust comes through both pipes)? Smoke disappears after some idle minutes.

The engine itself runs fine when it's not too hot, no power reduction AFAIK. Idle is stable (no chainsaw effect like I had some time ago).

 

[hlweyl]

Have you had a leak down test done yet?

 

[RP-Motorsports]

Are you getting any air to come out after a red spike? If so, check your coolant overflow cap. It has to be double locked, or it will suck air, and cause an overheat. It took us a whole season to figure this out!

If you get no air to come out ("burp" all points in the front AND in the back), then check your water pump. I would say therm, but you said you removed it for constant flow. Are you using an OEM temp guage? I would hook up an aftermarket one.

 

[NSX-Racer]

Have you had a leak down test done yet?

Do you mean a coolant leak down or something else? AFAIK I have no coolant leak.

 

[NSX-Racer]

Are you getting any air to come out after a red spike? If so, check your coolant overflow cap. It has to be double locked, or it will suck air, and cause an overheat. It took us a whole season to figure this out!

If you get no air to come out ("burp" all points in the front AND in the back), then check your water pump. I would say therm, but you said you removed it for constant flow. Are you using an OEM temp guage? I would hook up an aftermarket one.

I already read what you wrote in another thread about the overflow cap. Mine seems to be okay and was always full locked. Water pump was checked when the timing belt has been changed. Does changing the OEM temp gauge solve the problem? I guess the ECU (max rpm reduction) isn't related to the gauge but to the sensors. And I also guess the water gets too hot no matter what sensor or gauge I use.

BTW: Thanks for all the hints - keep it coming! :smile:

 

[Hrant]

I was going to suggest the OEM temp gauge as well just as another possibility given all the other steps you have taken. And we all know the oil gauge's reliability ......... Can you test the water temp at the track with an external gauge before changing the OEM unit? That would be a good validation of the readings.

 

[DutchBlackNsx]

Does your car still have the OEM coolant tank?

Does your system keep pressure?

 

[NSX-Racer]

DutchBlackNSX: Two times yes.
Hrant: Yes, we checked the temp with a digital gauge (in the overflow bottle) and the reading seemed to be correct.

 

[Hrant]

Hmmm, so the external readings match the gauge reading. OK, just total shots in the dark.

Have you tested the volume of water that your radiator is holding? Could there be any blockage someplace?

Do you have Dali's radiator shield by any chance? :wink:

Since many of us have this problem at one track here in NorCal in summer months only, this is an intriguing scenario given the steps that you have taken already

 

[RP-Motorsports]

stock radiator right?

Also I know some people will wire the fans to always be on when the car is running, or to a toggle switch. But at track speeds, you should have enough air passing through.

 

[NSX 3.0]

Just a thought here... maybe the Temperature Gauge Sender might be on the fritz.

 

[NSX-Racer]

stock radiator right?

No - special custom built competition radiator - but I had the same problem with the stock radiator too.

Next steps are: Another radiator with better cooling and another fan with more power - of course all other points you guys mention here will be checked before the next track event - also the gauge sender.

 

[hlweyl]

Do you mean a coolant leak down or something else? AFAIK I have no coolant leak.

A leak down test is different from just testing your coolant system for leaks. This tests each individual cylinder's ability to seal by pumping compressed air into each combustion chamber through the spark plug hole. More sensitive than a compression check, it can show pesky head gasket leaks and even small cracks in the block.

good luck

 

[NSX-Racer]

Thanks for the info - I just had the head gaskets replaced - I hope they are not blown already or that the block has leaks but I will tell the techie anyhow.

 

[AU_NSX]

Just a thought,

I also had this problem. However a swirl tank installed to bleed air out of all the high points in the extensive cooling system plumbing has since cured all overheating. I have found that air bubbles or pockets of air in the radiator piping are generally the cause of the NSX overheating at the track.

I still have the factory radiator installed but with twin hi-speed cooling fans for when the car is stationary like waiting on the grid.

 

[nsxhk]

On a side note... I have a coolant temp gauge installed. After 7 laps on track, the coolant reach 103C. Is that high? I was too busy looking at the aftermarket coolant temp gauge and never got a chance to look at the oem temp gauge so I don't know if it's in the red zone or not.


Henry.

 

[NSX-Racer]

Any thoughts about the ignition timing that I mentioned in my 1st post?

Henry: AFAIR was coolant temp measured with an external meter was a bit below 100 C - so I assume 103 to be high.

 

[DutchBlackNsx]

I wonder how come you also get a 22.
Would be interesting to know your oil temperature.
You looked at oilpressure during high water temperatures throughout the whole rpm range?

 

[Dave Hardy]

Ignition timing can cause a car to run hot, but if it is within spec it would surprise me to see that be the cause. If you're going to be tracking your car, get a proper oil pressure and water temperature gauge. You can get both gauges for $100, so it's cheap insurance.

It doesn't sound like you've got gauge issues though, it sounds like you're really running hot. Make sure you have all of the air out of the system. A swirl pot as mentioned above is a nice way. You can also have the cooling system vaccum bled. Also, check the health of your cooling hoses and radiator.

You said that when the timing belt was done that the water pump was checked. You didn't say replaced though. I've seen Honda water pumps throw their impeller. Everything looks fine from the outside, but the impeller is spinning on the shaft inside.

I'd verify one more time that there isn't any air and that their isn't any obvious blockage (pinched hose, crap in radiator, trash covering air path, etc.), and if that doesn't reveal anything I'd look at the Water Pump.

 

[NSX-Racer]

I wonder how come you also get a 22.
Would be interesting to know your oil temperature.
You looked at oilpressure during high water temperatures throughout the whole rpm range?

Yes, it drops to nearly zero at full rpm - but that's not depending on the temperature - I have this drop down as long as I have the car and track it.
Code 22 is a front Vtec pressure switch failure which makes not much sense to me according to the engine temperature - but maybe someone here knows the whole story...

I have no clue about the oil temp.

 

[Larry Bastanza]

I really have to think about this one. Do you still have all the heater core plumbing in the car? Have you tried operating the heater when you start to overheat? Curious in this will help. Sure there are no obstructions in the airflow path in front and behind the radiator? I noticed you have a scoop in the hood right? As Dave mentions have you reviewed all hoses, especially in the tunnel for any pinching, etc?

Regards,
LarryB

 

[mitchell smith]

you said that the car was over heating and the cylinder gaskets were replaced. Rule of thumb that the cylinder heads get inspected and checked for hair line cracks (pressure tested) and machined if needed when replacing the head gaskets. always check the engine deck with a straight edge. after the new head gaskets are installed and the engine bleed out we at Mechanics Direct Modifiers will test the engine with an emission machine to make sure no combustion gasses are getting into the cooling system. at that point you are sure the cylinder head job is done correct. :smile:

 

[the nsxnut]

Wolfgang, one other completely different approach:
The overheating can be a symptom of a problem that is not related to the cooling system... I have seen conditions where the NSX showed signs of overheating that was the result of internal engine issues that are diagnosed by a leak-down test. This measures the cylinder/head integrity by testing the ability of the motor to hold compression when the piston is static, at the top of it's stroke. If you've done everything to the cooling system already, and its still overheating, you might check compression and leak down to check for cylinder health. Good Luck.

 

[NSX-Racer]

Thanks to all you experts for your thoughts and ideas - I will translate all these and give them to my techie as soon as he returned from his holiday (another 2 weeks - bummer).

 

[NSX-Racer]

Just to inform you of the latest news: Techie checked for air bubbles (none), leaks (no exhaust in coolant) and told me that a leak down test as you described here isn't necessary because if I would have had a leak that would be detected by that test I couldn't have driven like I did before.

Water pump works okay, hoses are okay, so the next guesses and steps are: Seems that the custom made radiator has enough volume but a different flow pattern than the stock radiator (water flows too fast through it to get really cooled down). So I'll get the next custom made radiator at the end of the week with a different flow pattern.

Techie says that an oil cooler would help to decrease the overall engine temperature (and therefor the water temp too). So he'll mount an oil cooler near the radiator at the front with hydraulic steel lines on the underside of the car (where the A/C lines are) to the back. A/C lines will be removed because I have no A/C components anyhow.

The two horn thingies in front of the radiator will be placed anywhere else because they may theoretically disturb a bit of the airflow (just a guess).

A stronger fan will be mounted behind the radiator. A custom made air deflector will be made for the front compartment to lead the hot air through the vented hood. The side scoops at the back will get some custom made inserts to lead the air where it is really needed (intake, brakes, engine bay).

When all that is done I will check if there will be a track day nearby at Hockenheim or Anneau du Rhin to test the effects of all this work. The weird thing is that the car didn't overheat even during very spirited street driving. We even drove in 2nd gear with about 90 km/h close behind a truck on the german autobahn for about 20 minutes without any heat problem. If you don't track the car like I do it is likely that you won't have any problem at all.

So the only overheating test is a track - the more narrow and slow the better.