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 cooler/filter. 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.