Plumbing counterintuitive? Coolant / plumbing experts weigh in? Oil cooler?

[Wild Turkey]

I know there has been some discussion on the cooling system recently, but I just noticed something very odd while changing the coolant hoses in my '01 NSX. 19522-PR7-J02 "Hose A bypass" exits (the block?) winds around in front of the thermostat, goes up and through some piping that's welded to a crankcase breather and then runs back down, practically crossing over itself and connects near the thermostat via 19524-PR7-A01 "Hose C bypass". It looks very strange - why not skip the runaround (and an additional coolant hose) and just connect directly since there are no other connections in between? Heating or cooling the crankcase breather?


In the pic, "Hose A bypass" is on the right and goes under "Hose C bypass" as it comes back around. I'm tempted just to plug "Hose A bypass" into the block where "Hose C bypass" plugged in and skip the extra plumbing and Hose C bypass. Will my cooling improve with the lowered resistance? Could I have saved the $10 for "Hose C bypass"?

Who am I kidding? I'm too chicken to not plumb it as Shigeru intended. But I'd love to learn what is going on here.

Bonus question: I got a nice set of tools for accessing those hose clamps from odd angles, but how do I get to the clamp on 19506-PR7-A01 "Hose, RR WATER". The clamp "grabbers" are on the bottom. I can see why, to avoid impinging on 19506-PR7-A01"Hose, RR WATER" beside it and 79728-SL0-A00 "Hose Water Inlet (engine) above it. But how do I get to it with that {air injector?} line running right in front/under it?

 

[Old Guy]

I am not going to wade into the piping mystery associated with the stuff around the NA2 throttle body. Even with my little coolant system map and part number list it was hard enough trying to keep track of the 'new hoses go where/' around the throttle body let alone venture into the 'I can do better world'.

With respect to accessing the release tangs on the hose clamp, what kind of tool are you using? I used one of these for most of my hose removal. I tried the cable style removal tools; but, had little success with them. Perhaps because I got a set that was too flimsy.

17000 Long Reach Hose Clamp Pliers

Overall Tool Length of 17" Provides Extra Long Reach.

www.lislecorp.com

I also have two rather large heavy needle nose pliers, one with a long straight and one with a long bent nose. I might have used the bent nose plier to squeeze the tangs and rotate the clamp up and then use the locking pliers to hold the clamp open; however, I am thinking that on this one, after the hose was removed from the firewall side I went Rambo and cut the hose off the spigot. With the hose out of the way this gave access to the clamp tangs to allow removal of the remaining portion of hose on the spigot. When the hose went back on I think I positioned the release tangs slightly differently - more to the left side of the engine. However, this could be false memory.

Have you done the heater hose yet - the long one that snakes up behind the EPS rack to the heater valve? I left that one for a future day because I could not even see the release tangs on the clamp at the bottom end. I also had the same problem with the short hose on the oil cooler. I could see the release tangs on the clamp on the far end up could not access them. I did this in late October and it was getting cold with a risk of snow and I was afraid of running out of time before I had to drive the car to the storage compound for the winter.

 

[TANTO]

Just happen to be replacing a whole bunch hoses on my RDX thus my "hose replace kit" was there for the capture. I've used every one of these tools in the last few weeks. Longer yet handles like the Lisle above would be nice.

 

[Wild Turkey]

Answering my own bonus question: There is no way to get a tool on those tangs without removing the air line, which was only about 5 minutes once the main 2 hoses were removed. Should have done that right off the bat. I made a mistake when reassembling, putting the hose on and then trying to put the air line back on. Oops. Engine side, air line, firewall side.

For tools, I bought a hose clamp pliers set on amazon, which included one of the cable operated ones, & I'm sure glad I did. I used several of the pliers with different ends for the different clamps. They had small rotating clips that grabbed the tangs, allowing me to move axis of the pliers while the tangs were still clamped, and they lock holding the clamp, making them easier to move around. Not awesome quality, but good enough for this DIY turkey.

I've done the rad, the tunnel below, and the engine bay ones with the thermostat. I'll tackle the heater hoses & the oil cooler later this week & see how they go. I'll have to make a thread when I'm done.

Still hoping for a cooling expert to explain that labyrinth by the intake.

 

[Wild Turkey]

Heater hoses done (little one behind the valve is a bugger!) but the 2 oil cooler hoses look like quite the chore to change! I can't see how to access the one end deep inside, even if I remove the oil cooler. Assume I'll lose some oil with that as well?

Suggestions welcome.

 

[Honcho]

I have been meaning to get back to you on this, but the week has been nuts. I'll post more shortly.

 

[Honcho]

Time to solve the plumbing mystery. The "bypass" circuit you describe is the idle control system coolant pathway. It's the same path on both the 91-94 and 95-05 NSXs, but it covers different components between the two versions.

On the 91-94 NSX models, the engine uses three components to manage the air intake and idle system: the FITV (fast idle valve); the EACV (electronic air valve) and the throttle body. For reliable operation in cold weather conditions, hot coolant is tapped right off of the rear head coolant exit pipe and passed through all of these components. It follows the following path: FITV --> EACV --> Throttle Body --> Water Jacket. You can see the pathway below.



On the 95-05 NSX models, the DBW throttle body eliminates the need for the FITV and the EACV since the throttle plate now controls idle. Thus, the hot coolant goes from the rear head directly to the throttle body and then exits into the water jacket. The "connection in between" those two hoses in your photo is the throttle body, which is not between the hoses, but after them.

 

[Wild Turkey]

Thanks for your excellent explanatory pictures @Honcho, but I was not clear enough in my question. I understand the engine parts of the plumbing and the part "after" which is the throttle body.
My question is the "labyrinth" pipe adjacent to one of the crankcase breathers, which I showed in my 1st pic and have now circled in blue in your picture. What is it for? I see no reason for the (pink) hose-to-labrynth, labyrinth, hose-from-labrynth-to-TB, which practically cross over each other as shown in my 1st pic, when one hose as I've shown in green here would suffice. In fact, the 1st OEM hose is flexible enough to plug right in as I've shown it!

Thanks for any insight into this labyrinthine question.

 

[Honcho]

Ah ok, I see what you're talking about. Technically, yes you could just run one long hose from the rear head to the throttle body. However, Honda likely routed it through the metal bracket because they already had that part from the old car and/or they weren't comfortable with such a long run that close to the engine. If you look at all other long coolant runs on the car they are a combo of metal pipes and short rubber hoses.

 

[Old Guy]

Heater hoses done (little one behind the valve is a bugger!) but the 2 oil cooler hoses look like quite the chore to change! I can't see how to access the one, even if I pull the 3 bolts holding the cooler/filter. Assume I'll lose some oil with that as well?

Suggestions welcome.

From personal experience, I don't think there is any way that you are changing the oil cooler hoses without removing the oil cooler. That is why I included the special oil cooler bolts and the figure 8 gasket in my list of cooling system replacement parts. I got the oil cooler off and the outlet hose replaced. It was the clamp on the far end of the short inlet hose that stopped me dead.

 

[Wild Turkey]

Oil cooler coolant hoses replaced. But the labyrinth and its hoses around the throttle body look even more odd now that I've reinstalled them and see exactly where they went. It just seems so un-Honda-like to run hoses around for no reason (pink), when there is such a short path to connect (green). I don't think it's to avoid too long of a section of non-fixed hosing with a fixed metal part, as the entrance to the labyrinth for Hose A makes Hose A longer than if it just plugged into the Hose C inlet directly:

Perhaps @TANTO can save another pound by plugging Hose A bypass into the Hose C nipple, removing the labyrinth and Hose C, and replacing the two crankcase breather sections with one longer one. Or is this labrynth actually for something? @Kaz-kzukNA1 ?

 

[Old Guy]

Oil cooler coolant hoses replaced.

Inquiring minds need to confirm what it took to do that since I really should go back and replace the short hose since I gave up on that one.

 

[Wild Turkey]

Inquiring minds need to confirm what it took to do that since I really should go back and replace the short hose since I gave up on that one.

I couldn't find a nice thread with instructions, so I took a bunch of pics and I'll be posting it shortly. I sort-of put together a bunch of people's advice and changed a few things. It wasn't that hard - just need to do it in the correct order. I could do it in 1/2 the time if I had to do it again.

 

[Old Guy]

Looking forward to that.

 

[Kaz-kzukNA1]

I never got involved in the OEM coolant hose mandrel design so don’t know the definite answer.

However, if you serviced the coolant hose on any Honda cars, you would notice that Honda did put lots of effort preventing the EPDM hose from scratching against anything, including another hose.

With our NSX, Honda placed extra layer/protection tube around some of the hose body.

With your spec, you must have noticed (unless they were already lost) several special clips/holders on few hoses around the TH body to keep each hose away from other objects.

LEV with exh secondary air pump system has distinctive metal pipe running towards the front and rear bank exh ports.

All AT models including the later spec LEV have the ATF cooler nearby.

The 2 hoses in your OP are only used for the 97+ MT and AT models.

With 95 - 96 MT and AT models, simple straight hose (-J00) used at the 19522 position and the -A00 - the same one used on the 91 - 94 models were still in use on the 95 - 96 at the 19524 position but only one required and not two.

Considering all these aspects, may be the 'labyrinth passage' was required to keep enough clearance around the coolant hose for any spec.

Or, it was to assist the serviceability or for the future development project.


As a side note, each car manufacture has their own internal philosophy/rule on the design spec.

With the production car design, you may experience many ‘why??’ moments.

With our NSX, why the rear wheel width is so narrow or huge gap at the wheel arch despite Honda tested so many other ‘exotic’ makes/models during the development stage?

Why the piston design is fairly simple after spending R&D time on intake airflow with VVIS?

Why there is a slit/cut out at the rearward of the external B-pillar metal panel?

Of course there are genuine mistakes from time to time (personally, I think the original ABS has its own design flaw) but most of the time, there were good reasons for such design.

I'll leave the rest to Wild Turkey but please make sure to set the orientation of the hose clamp at the further side of the shorter hose as above.
Not great photo but hope you can figure it out.
The single pointy unicone facing the floor and towards the rearend.
The flat open tab towards the front.

Never tried but if you can access and have enough space, it 'may' help removing the hose connection block mounted on the eng deck.
New o-ring required though....


Kaz