Right, it's been discussed a little bit recently, and I was bored yesterday so I did it

Basically, coolant is circulated around the throttle body so that in colder weather, if it freezes shut, the coolant will thaw it out as the engine gets warm. In most of the UK though, it doesn't really get cold enough for this to be an issue, so this feature can be "disabled" by bypassing the throttle body, which should keep the throttle body cooler, so it doesn't heat up the intake air so much, which theoretically gives you more power. Can't say I've noticed a difference after doing it to my 1.8, other than the weight saving of a 4" long hose

Instructions:
1. Locate the throttle body coolant pipes. They're zinc pipes sticking out the throttle body, with black hoses clipped on. Follow the hoses - they should lead to the coolant system somewhere, I forget where.

2. Undo the clips, wiggle the hoses and remove them from the throttle body. Coolant will spill out, but not much if the engine has sat for a little while.

3. Remove the shorter hose completely (unclip, wiggle and pull) from the other end too.

4. Re-route the larger hose so that it goes where the smaller hose went.

So, instead of having a hose, then the throttle body, then a hose, you've just got a single hose

Pics:
Circled in orange are the pipes on my 1.8 post ford throttle body - yours may be in a different place, but they will look basically the same


Here's the other end of those pipes - you basically need to join these bits together with one of the hoses


This is how mine are now joined - hose is highlighted in red


I took those photos before clipping them properly into place, just FYI

Good work matey

So that last picture is just one of those hoses circulating back on itself?

And what are you doing the the gaps left with the TB? Just leaving as is?

Correct on both counts

You've got 2 hoses running to the throttle body, like II - I just took one off, then connected the TB end of the other to where the first one was, in an n shape

Nice one thanks, looking forwards to giving this a go, really hope it works, nothing better than free performance increases

nice one hughie. Also just so people know this can also be done to the v6 throttle body

Yep - can be done on all the throttle bodies in the world if they have coolant circulation same process for any car really

+30bhp woooo hoooo

Pretty good mod! I did this on the GT engine, at first I was going to do it the way you've done but I blocked off each pipe individually incase it effected the heater.

One thing I did note was the engine ran a hell of a lot cooler as I did this back in February.

You could do it that way too - makes no difference really The coolant was flowing between the pipes anyway, I've just taken the throttle body out of the loop Blocking those two little hard pipes instead of connecting them would work just as well

Just a caution, could possibly lead to erratic idle- it did to my v6 because there were now air bubbles in my tb where coolant used to be. I have heard this works with good sucess to other cars but can b a double edged sword for the v6

What the... the coolant doesn't mix with the air in the throttle body bypassing the coolant can not cause an erratic idle by itself, unless you're in a cold climate, I guess the idle control valve could freeze

Sorry if i explained it bad, not saying the coolant mixes with air, but rather you have air bubbles where coolant used to/should be, which has a negative effect on the iac ( iac is idle air control valve right?) I don't know how its makes things funny, but it did for me

The coolant and airflow are totally seperate - removing the coolant has no effect on the airflow, other than potentially cooling it down you may introduce a couple of air bubbles into the coolant system, but these will flow into the expansion tank next time you start the engine, and would have no effect on your idle speed

IAC is idle air control valve yes

EDIT: I believe our IACs are electronically controlled by the ECU (hence the 2 wire connector on it) rather than by the coolant, which would explain why my idle hasn't changed since doing the mod if anyone does it, and notices their idle is affected, try reconnecting it to see if it fixes the problem if it does, I'm mistaken and I'll amend the guide accordingly! Mine have been bypassed for about 350 miles now, not noticed any adverse effects

To be fair after doing more driving mines settling, the idles still high for the first 4-5 miles (warming up time) but besides that it's now dropping back down to it's usual idle range so I'm not complaining. I do notice it's a little better in the throttle response now as well

Isn't that perfectly normal? Every car I've ever seen does this due to the auto choke engaging until the engine warms up, then the idle drops?

Correct Phil - starting from cold, the IAC will be open allowing more air into the engine to help it warm up quicker

I was under the impression that these coolant hoses aided in less choke time, hence less fuel being used from cold. Removing them surely means the throttle takes more time to warm, meaning the car is on choke for longer and using more fuel than it should be.

Nope, never with the ones I've owned, I know this because I'm very particular about a cars idle, the warmer the weather the less the auto choke kicks in for me, and once I'm driving normally the idle always goes down to roughly 800-850 now it tends to hand at 1100 for the first 4,5,6 miles of driving dependingon weather, I've not driven an awful lot since not being at work so can't be certain, it's certainly nothing I'm concerned about! Just something I've noticed.

@Leth - Well that's what I thought might be happening now but *shrug*

Not the case - you have an O2 sensor in your exhaust, so if the engine is running unnecessarily rich, the ECU will pick up on that and alter the fuel accordingly. My air/fuel ratio gauge tells me so

so your car doesn't idle higher than usual when it's cold?

Mine has always idled at about 1000-1500 when first started from cold, until the temperature needle has moved slightly, then it sits around the 850 mark. This has not changed AT ALL since bypassing the throttle body coolant loop

This is one of those simple mods though, that if it has adverse effects, you can just put the hoses back to normal - no harm done

Nice guide Hughie I did a search for this mod and it seems quite well known for different engine makes out there... so for the sake of complete noobs like me I've linked one page I thought was particularly nice and clear even though it's for a totally different engine (type of engine, even!)

http://www.rotaryinsider.com/diy-tac38/throttle-body-coolant-bypass-gap29.htm

Bottom line:

I think I'll be doing that Hugh see what the difference is then as well! (When I can find a new tube that isn't split of course)

What I was saying though, was my car idles higher the colder it is, what I'm saying is once I get moving, the car returns to a normal idle very quickly compared to how it does now, for instance this morning my cars idle didn't return to normal until I pulled in at work, which it's never done before it started 2000, 1800, 1500, 1100, 800-850 as my journey went on, now it was rather a cold morning - Must say though the car was on something this morning it was very responsive

I reckon it's due to the colder morning but let us know your results if you put it back

we'll see I guess Have to say frustrations aside really enjoying all this fiddling with things! Best way of learning all this.

Does the throttle body not get heated buy the heat in the engine bay anyway???

Must get pretty hot back there, and if you've got a good rush of cool air coming in, a small amount of water at 84 degrees C being near it for a fraction of a second on it's journey into the engine probably doesn't make that much difference to the performance...bearing in mind the whole area is heated to nearly that anyway...

Yes Marc you're right

Can't say I've noticed much difference in performance myself, however when driving today, before it was up to temperature, the car did stutter/hesitate a little - could possibly be related, so I'll try again when I leave work tonight. If it happens again, I'll re-run the hoses and see if that cures it

What I know for sure, on KL engines at least, is that the coolant warms the IAC and without it, it doesn't work properly, only an issue at cold temps really.

Whether it's the same for KF engines, I do not know.

Possibly the same on the BP engine if that's what I experienced today - I'll see if it happens later, and if it does, I'll plumb the coolant back into the throttle body and see if that cures it