*** incorrect expansion pressure cap being supplied by Honda ***

[ScienceofSpeed]

We recently discovered that Honda has been including the incorrect coolant expansion cap for the NSX in the bag with the correct NSX part number (19045-pr7-j24) for the factory expansion tank. We’ve informed Acura’s part distribution system.

The plunger length is too short and does not correctly seat in the neck of the expansion tank. This could lead the coolant system to not hold adequate pressure and may result in the engine overheating in extreme use. The correct cap is on the left (gold finish) and the incorrect on the right (black finish). The correct cap has a seal to seal dimension of 16.9mm, the incorrect cap 15.4mm.

Please contact your Acura dealer or the source you purchased from for a replacement if you have the incorrect cap.

 

[nis350]

any idea when did this mistake start?

 

[Stephen@NCAutoUSA]

Great catch Chris.

 

[skafia]

Great catch. I did notice many NSX owners started receiving the black cap from Acura but I attributed to that being an NSX-R cap that superseded the previous part.

 

[drew]

> The correct cap has a seal to seal dimension of 16.9mm, the incorrect cap 15.4mm.

Can you verify the measurements? I cannot determine what part of the seal is being measured.


Which seal, the one on the plunger or the one in the cap?

 

[nis350]

so are all the black caps bad or only the recent ones?

Great catch. I did notice many NSX owners started receiving the black cap from Acura but I attributed to that being an NSX-R cap that superseded the previous part.

 

[DocL]

SOS is the best!!!

But imagine now if OEM radiator caps aren't available? WTF.

 

[goldNSX]

Just wondering: is the bottle neck any different and the shorter cap plunger is for a different bottle?

EDIT: I've measured the plunger (overall) length of my 2006 (replaced back then, still on the car) and my 2018 (new part in stock) and both are around 20 mm long IF you remove the play of the plunger and measured from the top of the cap to the surface of the round gasket.

So if it was wrong, it was wrong since more than a decade or since just recently.

 

[BB]

I've had the black cap on my car for many years. It was originally bought from Japan as an NSX-R part. When I measure it I get slightly over 15mm between the two seals. So if this is truly an error on Honda's fault, the problem has been present for a long time.

 

[drew]

I measured mine as well, and I get ~15mm. No cooling or coolant issues. My car is 100% JDM and the cap has been on for a few years.

I wonder if they changed out the spring to compensate?


Has anybody done a pressure test on the cap?

 

[goldNSX]

Has anybody done a pressure test on the cap?

As far as I've understood it's a cap/bottle combo thingy rather than just the cap but you could still to the test with some small adaptations.

 

[nis350]

got the black color cap a few years back... no change in temp at all under normal driving condition.

I imagine it would lose all the pressure being in smaller size.... wouldn't that at least increase the temp a bit?

I measured mine as well, and I get ~15mm. No cooling or coolant issues. My car is 100% JDM and the cap has been on for a few years.

I wonder if they changed out the spring to compensate?


Has anybody done a pressure test on the cap?

 

[goldNSX]

I've got a coolant pressure tester kit recently and tested the old and the new cap. The old one holds 1.0 bar while the new one holds 1.05 bar.

 

[nis350]

so the new one is better....

I've got a coolant pressure tester kit recently and tested the old and the new cap. The old one holds 1.0 bar while the new one holds 1.05 bar.

 

[goldNSX]

so the new one is better....

But just by 0.05 bar. Considering that the old one has been 15 years in use, that kind of difference is to be expected.

 

[nis350]

that's good to know that the newer version with black cap/smaller seal is fine. Thanks for the info.

But just by 0.05 bar. Considering that the old one has been 15 years in use, that kind of difference is to be expected.

 

[goldNSX]

Not sure if it helps but the new Civic Type R cap is 1.3 bar. Not sure if it fits but worth a try.

 

[RYU]

In the last 3-5yrs since running the MASiV radiator I haven't coolant temps get over 205-210F. In general it stays easily around 190F at the track and hovers between 176-185F on street - it's' almost too cool. It stayed below 208F in the hottest of hot California track days include NSXPO Palm Springs and the most recent XPO at Thunderhill. Honda 50/50 coolant (what I run) doesn't boil until about ~230F. So you don't really need to raise the system pressure if you're never getting the car that hot to begin with.

Just my $0.02.

Side note: Props to Chris for sharing this with us. He didn't have to goes to show what kind of guy he is! Thank you

 

[RYU]

Not sure if it helps but the new Civic Type R cap is 1.3 bar. Not sure if it fits but worth a try.

In my opinion if you need a 1.3 bar cap you might have fundamental cooling issues that could be better solved with better equipment. I'm just not a fan of raising pressure as it stresses out all the components in the cooling system including the head gaskets.

 

[goldNSX]

In my opinion if you need a 1.3 bar cap you might have fundamental cooling issues that could be better solved with better equipment. I'm just not a fan of raising pressure as it stresses out all the components in the cooling system including the head gaskets.

Not necessarily as some cars come with 1.3 bar caps. But I agree with you that a higher-rated cap is chosen by design (of the other components as well). On the other hand why didn't Honda design the cooling system of the Civic Type R in a way a 1.1 bar cap could be used?

 

[RYU]

On the other hand why didn't Honda design the cooling system of the Civic Type R in a way a 1.1 bar cap could be used?

I have first hand experience with the CTR. The struggle for cooling IS REAL. I've never had a car that has been so notoriously difficult to cool. Just look around the CTR message boards and you'll see what I mean. The cooling problem is pervasive. Honda has tried everything... adding the 1.3bar is a testament to how far they had to reach to get every Nth of cooling out of the car. It's still not nearly enough.

Many guys here at have called off tracking their CTRs in the summer entirely. I can overheat a CTR on a 65F ambient day and get the temps to 230F in about 3-5 laps. Just imagine if that was a 80-90F day. It's more like 1-2 laps at best... Many people are aware of the "limp" mode when overheated. They don't even realize the car enters limp mode at 250F+. It's crazy....

 

[RYU]

In fairness.. if you drive the CTR and make use of the low end torque.. you can stretch out the time out on track quite a bit. Driving style can fix a lot of cooling problems with the CTR... but still...

 

[RYU]

Not necessarily as some cars come with 1.3 bar caps. But I agree with you that a higher-rated cap is chosen by design (of the other components as well).

If you need a 1.3 bar cap IN THE NSX... it's a bandaid.

 

[latzke]

any idea when did this mistake start?

I've had the black cap on my car for many years. It was originally bought from Japan as an NSX-R part. When I measure it I get slightly over 15mm between the two seals. So if this is truly an error on Honda's fault, the problem has been present for a long time.

I replaced my coolant bottle and cap with new in 2012 (from Acura of Peoria, aka oemacuraparts.com; a well-known / reputable / high-volume parts department). At NSXPO HPDE that same year I blew a head gasket. Afterwards my testing revealed the new cap and new bottle (together) were not holding correct pressure. Old cap and an aftermarket cap (generic from AutoZone) did hold correct pressure. I still have both OEM caps and they differ in the way Chris (SOS) describes. I highly suspect this cap was the cause of my head gasket failure, this incorrect cap issue has been present for a long time, and all of the black caps should be considered suspect.

Wish I had posted about this back then (so others were alerted in 2012, not 2019) but I just figured mine was a one-off issue. Probably a good number of people are driving around on the street with these, without issue...but at risk if they drive the car hard enough or on hot enough day.

 

[Honcho]

I replaced my coolant bottle and cap with new in 2012 (from Acura of Peoria, aka oemacuraparts.com; a well-known / reputable / high-volume parts department). At NSXPO HPDE that same year I blew a head gasket. Afterwards my testing revealed the new cap and new bottle (together) were not holding correct pressure. Old cap and an aftermarket cap (generic from AutoZone) did hold correct pressure. I still have both OEM caps and they differ in the way Chris (SOS) describes. I highly suspect this cap was the cause of my head gasket failure, this incorrect cap issue has been present for a long time, and all of the black caps should be considered suspect.

Wish I had posted about this back then (so others were alerted in 2012, not 2019) but I just figured mine was a one-off issue. Probably a good number of people are driving around on the street with these, without issue...but at risk if they drive the car hard enough or on hot enough day.

I wonder if this is why mine blew at the track too. I had just replaced the cap with this part as part of a radiator change just before NSXPO...