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Frustrating month

222k miles and still the first radiator?
I don't wanna be a smart ass but a full refresh of the cooling system is a must on cars with higher mileage. There were too many reports in the past of blown radiators, coolant hoses and cracked coolant bottles which lead to HG failures. Just a word of precaution to all high-milers out there.
Good luck! Hope it won't be too bad.
 
[MENTION=7151]mskrotzki[/MENTION]

How did your OEM radiator fail? Did the end tanks crack , the seal between the end tank and the core fail or did the core fail? I had an older Euro product that had composite end tanks bonded to an aluminum core. The bond failed allowing separation of the end tank from the core on that radiator . Fortunately the failure occurred just after I parked the car on a really hot day. The coolant temp must have spiked with the fan and pump shut off so it was just a big coolant release in the parking lot. I was looking at the NSX OEM radiator and the end tanks are crimped to the core. I could see the possibility that the gasket at that interface might develop a leak at some point; but, I think that would unlikely be catastrophic. If the plastic end tanks cracked that might be an plastic ageing issue and could potentially be an issue for all owners.

Were you running an OEM pressure cap on the expansion tank or an aftermarket cap which might have had a higher release pressure?
 
If the plastic end tanks cracked that might be an plastic ageing issue and could potentially be an issue for all owners.
Kaz has plenty of pics of leaking radiators in his blog on the UK forum. They tend a crack in the lower plastic end tank where the coolant hose attaches.
 
[MENTION=7151]mskrotzki[/MENTION]

How did your OEM radiator fail? Did the end tanks crack , the seal between the end tank and the core fail or did the core fail? I had an older Euro product that had composite end tanks bonded to an aluminum core. The bond failed allowing separation of the end tank from the core on that radiator . Fortunately the failure occurred just after I parked the car on a really hot day. The coolant temp must have spiked with the fan and pump shut off so it was just a big coolant release in the parking lot. I was looking at the NSX OEM radiator and the end tanks are crimped to the core. I could see the possibility that the gasket at that interface might develop a leak at some point; but, I think that would unlikely be catastrophic. If the plastic end tanks cracked that might be an plastic ageing issue and could potentially be an issue for all owners.

Were you running an OEM pressure cap on the expansion tank or an aftermarket cap which might have had a higher release pressure?

As Gold mentioned, they crack at the plastic tank area near where the lower coolant hose attaches. He likely had a leaking unit already due to the mileage. Kaz has documented this on dozens of NSXs, which is why he recommends replacing the radiator on a regular schedule. He views it as a consumable part like brake pads, but with a much longer change interval. Based on the ones I've seen, I would say around 100,000 miles is a safe radiator change interval for most NSXs. Of course, this can change depending on usage and conditions. Heavily tracked cars would be shorter (though most of those already have aftermarket rads) and the garage queens/car show cruizers would be longer. If Mark had a massive pressure spike due to the HG/boiling coolant, it would easily rupture the already weakened plastic and dump several liters of coolant in short order. It's amazing how quickly lots of coolant can blow out of the system under pressure- I dumped my entire coolant bottle full in less than a second when my HG blew on the track.
 
I've changed my still working OEM radiator after 29 years and 125k miles recently and went for a Koyorad. After 125k miles it has done its duty, no fun running out of coolant on a trip. Most OEM radiators show leakages between 125-150k miles in the UK. You've even higher temps in the US, so I'd expect it to fail earlier. Heat-cycles is the keyword here. The famous coolant bottle already showed cracks after 14 years again but without leakages so far. Changed for the 3rd one. Again heat-cycles. If you remove the engine cover then the sun will 'help' to age it even more. Hoses every 15 years.
These values are for a normally driven NSX with around 8k miles per year on average in a moderate climate (Europe).
 
The original radiator seemed to be leaking along the bottom, right near the lower hose connection. Thermostat also was stuck shut, as trying to put more H2O into the system (after it cooled) was a no go -- just stayed in the expansion tank.

The 1st Koyorad leaked in a tube near the lower part of the radiator.0627201123_Burst01_resized.jpg (This picture is upside down.)

Now my issue is to get the car about 80 miles back to the shop. Anybody in my area have a line on something less than $80.00 to load and $4.00 per mile?
 
mskrotzki said:
The original radiator seemed to be leaking along the bottom, right near the lower hose connection. Thermostat also was stuck shut, as trying to put more H2O into the system (after it cooled) was a no go -- just stayed in the expansion tank.

The 1st Koyorad leaked in a tube near the lower part of the radiator.

Crazy that the Koyo leaked too- wonder if that was due to the over-pressure from the HG?
 
Crazy that the Koyo leaked too- wonder if that was due to the over-pressure from the HG?

Never got to start the engine with the first Koyo -- never able to fill the cooling system. The Koyo looked like it was taking a leak all over my garage floor. It took a while for the SOHi to find another one -- eventually came from Pennsylvania.

Paul -- do you have any thoughts on getting my car to Peyton?
 
Well -- maybe my luck is beginning to change. AAA just called and said they would flatbed the NSX from my garage to Peyton under our premium membership: cost $0.00.

I miss driving it.
 
Crazy that the Koyo leaked too- wonder if that was due to the over-pressure from the HG?
My thought too.
The engine failed to start after the Koyorad has been fitted but it was tried to start and that might have been enough. The cap can't cope with a pulse of pressure but I'd expect a hose to burst first. Koyorads are pressure tested in the factory three times.
 
Sounds like you are in good hands.
Based on dealing with several overheated NSX engines as well as same phenomenon you described,
would like sharing my experiences and one of the worst case that my friend dealt with.


Due to possibility of multiple issues and you don't want repeating the same tasks after placing everything back in place, would recommend proceeding step by step.


The thermostat
Never seen one stuck closed and being as the main cause of the overheating issue on any NSX engines.
So far, always stuck open on many of the original thermostat design.

After replacing to the new design one, seemed to be fine and no longer taking ages to warm the engine up.

If overheated or suddenly lost coolant, it's my own policy to replace the thermostat even if it was new.
Quite often, the excessive heat can generate lots of powder like residue in the cooling system and
it seems that thermostat doesn't like big thermal shock that requires the centre plunger to move quickly from full open to close.

I think your initial report of stuck closed thermostat is very likely to be the result of losing coolant suddenly due to cracked radiator and
thermostat exposed to excessive heat but suddenly cooled down as no more contact to the coolant.
Once closed, no longer functioning.
Not the direct factor causing the overheating.


The radiator
Mentioned the following so many times on the NSXCB forum.

The OEM radiator is just another consumable parts, just like the oil filter but at much longer service interval.
One of the most neglected service on any car make/model.

I replaced so many NSX radiators in the past and even replacing one for another owner at the moment.
All of them were seeping the coolant slowly without being noticed by the owner because the coolant tends to crystallise and won't drip on the floor once the water has evaporated.

Also, by now, almost all of the original ones are no longer holding the original cooling efficiency.
Not a big problem on 3.0L C30A engine on street driving condition but the owners of 3.2L C32B engine or those driving hard should pay much more attention.

Depending on the shape of the circuit or the driving environment, in hot summer, 1 timed lap would force you to take cooldown lap next even without any engine power modifications.


The knock sensor
If doing the head gasket job, please take a look at the plastic holder of the knock sensor cable after removing the intake manifold.
If overheated or driven really hard all the time, almost always the plastic holder was melted.

Melted holder itself is not a big issue but please double check that the cable sleeve/insulator is not hardened or the cable itself is not damaged (will trigger CEL).

By the way, never touch the knock sensor itself unless 100% you have to.
Not even try removing the sensor connector.

It seems that being placed within the V-bank, they (one for each bank) are exposed to high temperature resulting in fragile plastic/metal bonding at the sensor body.
If you touch the sensor or even try disconnecting the wire connector, very likely the sensor body will split at the seam of the green plastic connector and the metal piezo sensor body.

If you ask S2000 owners about the knock sensor, they will know what I'm talking about.

They are designed for the specific resonance frequency window so OEM one is quite expensive.

If overheated and doing H.G., you may want considering replacing them anyway if never replaced in the past.
Though, you can wait for the CEL and replace them later by just removing the intake manifold.


Good Fuel mixture
As you can't even fireup the engine, will leave the feedback software loop out of scope.

On fireup, there is specific map mainly based on the coolant temp for the INJ timer.
Adjustment for RPM/voltage/etc applied and triggered at specific crank angle fuel/IG timing.

You have confirmed that the fuel pump resistor is not the cause.
The phenomenon you mentioned was experienced by many owners and even helped road rescue people while one owner was stranded on the way to his holiday
so was hoping the same on yours.

I would check the fuel pressure at this stage.
You don't even need cranking the engine for this.

Proper gauge would be best but I know many owners used the cheap one from ebay/amazon/etc successfully for the quick testing purpose.
It's the one that can be mounted directly on top of the fuel filter banjo.

Personally, I won't install it as permanent solution but for a quick check, good enough.
Just ask someone to turn the IGSW into P2 On then back to P1 ACC and repeat it several times to prime the fuel system while checking the pressure gauge.

As mentioned above, on fireup, ECU uses coolant temperature based map.
The sensor in use is called TW sensor.

This is different from other 2 coolant related sensors (Sender unit for the temperature gauge and the Rad fan sensor for the fan control unit).

It's the one located at the front bank with black connector sleeve, below EGR valve.

On several NSX engines, this sensor failed and sent cold temperature data forcing ECU to use very rich mixture.
Some owners experienced hard time starting the engine (but at least, was able to fire up so probably not the case on yours).

If this sensor fails (and if you manage to start the engine), the engine will never goes to the idle window and stays higher at about 1,000+ rpm even when the engine has fully warmed up.

As mentioned, probably not related to your case but since you overheated the engine, worth checking the sensor output at room temperature as it's located in quite difficult to access area.
Not easily replaced with the engine inside the engine bay.


Did you read the error code even if you didn't see the CEL?

Could be too late as you may have already disconnected the battery but there are multiple error codes that won't trigger the CEL but stored in the memory
unless failure condition detected twice within the same drive cycle or in consecutive cycles.

If the engine was cooked to the point you can't even fireup again, you may have stored some error codes at the time you first overheated the engine massively.

I do hope your CRK/CYL sensor is still healthy.


Not just fuelling related but when you were about to park the car after test driving with the new replacement radiator, did you notice lots of smoke or awful smell of exh fume?


Good Spark
Have you inspected the spark plugs?

It's almost impossible to fail all spark plugs and IG coils at the same time so not the direct cause but may support you in diagnosis.

On almost all of the engines that required head gasket job, would notice some unusual deposit left on the centre terminal/insulator area of the plug especially at the cyl where the head gasket was breached.

Also, at the same cyl, the very spark plug would smell really-really awful.
Can't describe it well but it's like you don't want keep smelling it for more than 5sec.
Almost like choking yourself.
It was like the smell of Qualify session special fuel used by the Ferrari F1 team in 80s'….


Normally, it would result in multiple misfire and very rare not being able to fireup at all (like yours) but some owners ended up not being able to fireup when their ignitor module failed.
Heat soaking can trigger this failure mode but since you parked the car overnight and then tried fireup so probably not the case but worth keeping in mind.


Good Compression
Hope you double checked that it was safe to fireup.

On many engines with the head gasket issue, the owners didn't even notice it and were able to keep driving without temperature issue under street driving condition.

They only noticed it when driven hard through mountain road and noticed that the coolant was pushed out from the tank overflow tube.
They managed to keep driving without any further loss of coolant or no abnormal temperature noticed while driving on the motorway or city driving.

If your engine is so bad to the point even not being able to fireup, then DO NOT carry out the compression check even on the cold engine.

Instead, use the leakdown test but on the cold engine.
If the engine is so bad, it would result in big leakage and should be able to hear the hissing sound through the oil level dip stick pipe, etc.


Followings are what my friend dealt with.
Hope yours is not that bad.....

On one engine, the owner lost coolant on motorway/freeway with cracked radiator lower tank and it even partially locked the WP and let the TB to jump the teeth.

This was very rare case because my friend found out that the owner previously experienced overhearing situation with the coolant pushed out from the tank overflow tube few years ago but
no further temperature issue noticed so left it without doing anything.
Kept driving with no further loss of coolant since then.
Similar to what I mentioned above with the owners that didn't notice their head gasket issue.

With this NSX, the WP was still the original design so never replaced since leaving the factory.
Who knows what effect the first overheating had over that ancient WP.
Honda changed the design because there were reports of seeped coolant landing on the TB rib.

This time, the owner was not so lucky and the damages were massive.
At the end, the owner decided to swap the engine and even added some upgrades.

If you didn't see lots of smoke, no nasty exhaust fume and the spark plug didn't smell awful, then hope the potential damages are limited and other factors are preventing you from firing up the engine.


Kaz
 
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Wow, Kaz – thanks for the massive write up. It is above and beyond . . . .


The car is now back in Colorado Springs at the shop the replaced the TB/WP, spark plugs, gaskets and general 90,000 mile service. I printed out your whole reply and they seemed quite interested in it.


Thermostat.jpg

I think you are right about the thermostat. It certainly was stuck closed when I removed it. In fact the pin on the top was dislodged preventing it from moving at all. When I removed the cover something “snapped” inside – probably the spring snapping up and moving the pin outside its hole. At the overheat event the engine was very hot, yet the radiator fan, full on, was blowing “cold” air. In retrospect the radiator was likely empty, and the hot signal was coming from the engine compartment.


The first Koyorad leaked so badly it never filled up and the engine was never started until the second one arrived.


Looking from underneath the car at the front side of the engine, it appears the knock sensor holder is indeed melted. My understanding is this “don’t hurt the running none.” Is that true?


I checked the error codes and got a 4-3 and a 6. I know all about 6, so there was no information there. My understanding is 4-3 (PFI) doesn’t mean much – just thrown when the system doesn’t know what else to do. Is that true?


The spark plugs have approximately 164 miles on them. They are brand new.


The shop will decide what to do about compression/leak-down tests. I agree with you, but I’m not going to tell them how to do their job. At 77 years old I have finally learned not to tell experts how to do their work. I am NOT an expert.


Thanks again, and I’ll keep you and everyone else following this thread posted.


Mark
 
The knock sensors are on top of the engine block underneath the intake manifold and virtually impossible to see, if your looking up from underneath and seeing something melted it’s probably the crank sensor potting and it doesn’t hurt anything, all of the early cars are like that.

Hopefully the shop will have some good news for you.
 
The knock sensors are on top of the engine block underneath the intake manifold and virtually impossible to see, if your looking up from underneath and seeing something melted it’s probably the crank sensor potting and it doesn’t hurt anything, all of the early cars are like that.

Hopefully the shop will have some good news for you.

See -- I am NOT an expert. I'm sure you are right -- it is indeed the crank sensor, and, at least, I was right that it is a non-issue.
 
That's concerning to hear about the Koyo radiator leaking out of the box. Glad it didn't happen while driving, and glad to hear you have another one.

I'm keeping my fingers crossed for you that it could be something as simple as a crank sensor causing all of this! Keep us posted on what your shop finds!
 
Sorry to hear about these troubles MSKROTZKI, but you'll get her back on the road shortly!

Not exactly the most modern; but, my 2003 pilot does not have a level sender. Can you list some vehicles that do? Might be an interesting winter project to see if you could adapt one to the NSX using one of the aftermarket tanks.

Loss of coolant pressure is also an excellent indicator. I have one of these plumbed into an aftermarket coolant expansion tank and a bright LED in the cockpit to let me know:
https://www.pegasusautoracing.com/productdetails.asp?RecID=9749
 
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That's concerning to hear about the Koyo radiator leaking out of the box. Glad it didn't happen while driving, and glad to hear you have another one.

I'm keeping my fingers crossed for you that it could be something as simple as a crank sensor causing all of this! Keep us posted on what your shop finds!
Thanks for your kind wishes but:

sad.jpg

This is a picture I had hoped to never see. Flatbedded the car back to the place that did the previous work. They spun the engine over with the plugs out and coolant spit out of cylinders 2 and 3. i'm waiting on an estimate for both time and $$$$. I just spent $2800 for TB\WP and all the goes with it, along with a request for looking over the whole car and let me know if it needs anything. I drove it exactly 160 miles. This is becoming a very expensive summer.
 
Thanks for your kind wishes but:

View attachment 166055

This is a picture I had hoped to never see. Flatbedded the car back to the place that did the previous work. They spun the engine over with the plugs out and coolant spit out of cylinders 2 and 3. i'm waiting on an estimate for both time and $$$$. I just spent $2800 for TB\WP and all the goes with it, along with a request for looking over the whole car and let me know if it needs anything. I drove it exactly 160 miles. This is becoming a very expensive summer.

Wow, I'm sorry to see this. That's scary how quickly a stuck T-Stat turned into a blown head gasket. You're in the right place for advice, I hope to see a picture of her on the road again soon!
 
I'm sorry to see that it came to this.

I hope that shop knows what they are doing, the fact that they have an NSX engine dolly seems promising.

@Mac Attack that low pressure switch is a great idea, with so many hoses to potentially leak.

Paul Z. is one of the original factory-trained NSX techs. Mark is in good hands.
[MENTION=7151]mskrotzki[/MENTION] glad to see it's being addressed. Worst case you'll need to mill the heads and maybe hone the cylinders if there was enough wash-down. The heads do tend to twist on the NSX in cases of severe overheats, though mine was pretty bad and they remained flat. Unlikely your block warped due to the much larger mass of metal. But, Paul should check both surfaces for flatness. I'd also have him inspect the main bearings for damage and clearance. At your mileage level, it may be a good time to put new bearings anyway. At a minimum, you should have him replace the coolant hoses at the oil cooler- this is mandatory in Japan for cars that overheated due to coolant loss. Also, it's likely coolant got into the head bolt threads...four of mine were fully contaminated. Make sure he cleans them all out and uses new head bolts. So sorry to see this happened, but this is fully recoverable. It's a testament to Honda's design that even a serious engine event like this can be fixed to effectively like it never happened!
 
They spun the engine over with the plugs out and coolant spit out of cylinders 2 and 3.
Honestly, I've feared that due to the starting issues you've reported. With a bit of luck the engine didn't get damaged while trying to start it. As it takes its time to fill the cylinders with coolant overnight I think the chance of a water hammer was low enough to prevent further damage. At least I hope so. A water hammer would bend everything in the specific cylinder. I don't think such an event could have happened during 160 miles. A thorough inspection of the lower end is mandatory. Again, I hope it's fine and hope to see you on the road soon again.
 
KOYO radiator

Just had a major update / service done to my car, ‘92 GPW w/34,500 mi. which also included the replacement of the OEM radiator with a KOYO all aluminum radiator and now I’m seeing all this bad talk about how they’re a p.o.s..
I was under the impression they were the one to go to as an upgrade for better cooling and longevity.
Am I wrong and if so any suggestions?

Cheers
nigel
 
I don't think the KOYO is a p.o.s. I do think it got damaged some how in shipping. It leaked from the get go, and I couldn't even fill the cooling system, so the car was never driven with my original KOYO. Installing a radiator is simplicity itself, so I just come back to shipping damage. There is a note in the packaging to have you inspect it upon arrival. FWIW, I still think it is the one to go to.
 
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