I've called napa/orielly/autozone/allied auto and none of them have them. How the hell. Will contact Honda dealership tomorrow...

Anyone got some info on using random same diameter rubber hoses that may even fit better/easier?

 

You should be fine to just go to the auto parts store and get some with the matching diameter. I actually think I did do that.

 

Like @TheBasedDoge said, grab the hoses off the car and take them with you to the auto parts store. You should find one with the same inner diameter pretty easily. May have to cut to length.

 

They're a strange size. Auto parts stores don't typically carry it. They'll sell you fuel hose...which isn't correct.

IIRC its 8mm (5/16") hose? Right?

Look on Bellmetric.com. They should have bulk coolant rated hose in that size.

Also...use constant tension clamps (like the factory clamps). Don't use worm clamps.

 

The stores I called as mentioned no carry/ordering which was weird. I ended up going to Honda dealership this morning. Only one of many within a 30 mile radius had them and they only had 1 short one and 2 of the longer. I wanted to drive my car asap lol but I will keep that website in mind for future.

I reused the oem factory clamps. No leaks/weeping noted! I will also keep that in mind that hoses that use factory clamps I will not use worm clamps.

 

Not sure if this was considered but you could also have just bought a long piece of 5/16" hose and bypassed the throttlebody entirely - connecting the pipe on the intake manifold directly over to the IACV on the opposite side.

As I recall, running antifreeze through the throttlebody was done to prevent the throttle plate from potentially freezing shut in winter but I'm not sure why it goes to the IACV because that functions just fine without any antifreeze running through it. People have bypassed both of them for years with no issues. Also, not sure many of us drive an S2000 during sub-freezing temperatures these days.

 

The throttle body is heated to more quickly improve fuel atomization and then maintain that intake temp. There are benefits in terms of emissions.

I don't know how much real benefit there is regarding the "freezing over" during winter, in practical terms. If the throttle blade froze...then even with the coolant flow, the thawing would take some considerable time. I guess it may help keep it from re-freezing during the drive, though.

Honda IACV's traditionally use coolant flow (speed) as a way to then meter idle speed. If you have bubbles in the coolant, you often see a "hunting" idle (00-05 models).

Anyway, often the tricky part is finding 5/16" coolant hose.

Again, in my experience, parts stores typically only have fuel hose in this sizing. Since fuel isn't made out of coolant...and fuel's operating temp isnt 200+F....I wouldn't suggest using fuel hose to transfer coolant.

I belabour this because I've seen plenty of cars with 5/16" fuel hose being used as coolant hose lol.

 

ahh I've never heard that one about making the throttlebody hot having any positive impact on fuel atomization or emissions - can't seem to find any information mentioning it yet either so if you have a source I'd love to educate myself more.

At the moment that would seem counterintuitive as most efforts seem to point to lower intake air temperatures being all around better for combustion but I'm no mechanical engineer. I can say that on my first S2k, with the Hondata IM gasket and AEM V2 cold air intake (only performance mods I was able to do on it) fuel economy reliably improved slightly as it got 24-25mpg year round regardless of how I drove it. Installing that Hondata gasket blocks the cooling passage coming out of the head that would feed the throttlebody + IACV line.

I have read (granted this is going back to the early days of forums) many places that Honda heated its throttlebodies to help prevent the throttle butterfly plate from freezing shut during cold winter temps, and on older vehicles with a FITV (fast idle thermovalve) this also helped with cold starts. On the S2000 although I'm assuming pre-06 (haven't really looked into AP2's much since I've never been in the market for one) all have IACVs on the intake manifold, idle function doesn't seem to be impacted by not running antifreeze through it. I had that Hondata gasket on my old AP1 the entire 8 years I drove it and it never had any idle issues during any season (here in northern Utah we see anywhere between 0 F and maybe 110 F each year).

You raise a great point about the hose type though - AEM includes a length of some 5/16" hose with their V2 CAI to replace the factory metal piece with some vacuum lines and that coolant line welded together but I'd bought a longer piece thinking to bypass the TB before realizing that the Hondata gasket blocks that line entirely so there's no need for hose there at all anyway.

The AEM-provided hose piece is not long enough to have all the markings on it so I'm not really sure what it is... to my unfamiliar eye it looks like fuel hose though.

 

Tried finding the coolant hose at a marine (boat) store? Fuel hose is fine though for this application. Only caveat being it may get brittle in a few years. Certainly good enough while searching for the "correct" hose.

-- Chuck

 

MPG improves with LESS air. Less air = less fuel needed in order to reach the desired mix.

Let's say you want 14.7 parts air to 1 part fuel. If you reduce the air, the ECU will reduce the fuel to keep a 14.7 ratio.

Lets say you want 10:1. Same principle.

2:1. Same principle.

Examples of this....

If you drive at high altitudes the MPG improves.

Summer MPG is better than winter MPG (even if you disregard the time needed to reach operating temp or difference in fuel types). Hot air is less dense than cold air. 1 cubic foot of cooled air contains more air molecules than 1cuft of hot air.

Half throttle gets more MPG than full throttle even if fuel enrichment ratio stays the same.

In all cases, you're restricting the air and the ECU is dialing back fuel.

Not sure why your MPG improved with the mods you mentioned. The biggest apples-to-apples factor on MPG is your right foot. So...idk maybe you drove differently after you put the mods on. Or maybe since you had the car for longer, you stopped flooring it or letting it idle as much.

One solid theory is that since the ECU sees cooler IAT's with your mods, it will tell the injectors to spray less fuel and increasing the timing since cooler air will help with knock/detonation.

As far as the principle behind using a heated TB to keep the IAT's warmer and improve fuel atomization.... Fuel vaporizes faster in hot air than cold, right? If you leave a puddle of gas in a 90F garage, it will evaporate faster than if u did it in a 30F garage. **Don't leave puddles of fuel in your garage

For your IAC question....removing the coolant flow completely from the IAC would just simulate a constant flow. So...yes, disconnecting the coolant will not cause an erratic/hunting idle. Constant no-flow is still constant. The IAC just won't react like it would under specific conditions. You may never notice a difference because quite a few other sensors will affect idle speed.