RB25 and RB26 Coolant Crossover Tube

[fikemoo]

Hi guys ive made the decision to remove the cold start valve (IAC Valve) as im going to be running a link ecu very soon and i thought why not bring the car into the modern world abit more and use the ecu to control the cold start, now what id like to know is. the coolant passages that run between the intake ports on the rb25 and rb26 heads, are they linked inside the head or is the tube that is bolted and runs underneath the intake manifold in fact a crossover tube and this cannot be removed or blocked off?

 

I ask as im in the process of installing a rb26 intake manifold on my rb25 head and my adapter plates havent yet had the passages cut out of them so i thought i could use the adapter plates to block them off as my current intake manifold seem to get rather hot, ive tried searching for what feels like an eternity for a coolant flow diagram for the rb25 and 26 but i just cant seem to find one, well one that shows the coolant flow inside the block/head, any information would be great

 

thanks mike

 

Picture of pipe/tube in question:

Edited July 4, 2016 by fikemoo

[discopotato03]

That air valve your talking about is a dumb device that is generally fed power from the fuel pump power circuit . That way it won't heat up and open unless the engine/fuel pump is actually running . If it was simply wired to the ignition circuit it would heat up and close before the engine was even started if you didn't crank it .

Having that valve means the idle speed control valve doesn't have to be that big that it can pass enough air on its own to keep a stone cold engine running . If it was it would need very fine electrical control to accurately control engine speed . To a degree the smaller the idle air control valve is the easier it is to regulate it .

If the factory knew how to do this better with the technology of the day they would have done it . Today its all done with electric throttle/s so the earlier bypass systems aren't needed .

That water log you mean carries all the engine coolant out of the head and ducts it to the top hoses water outlet . 

[fikemoo]

Thank you very much for the reply and information. I had a feeling the water log would carry the coolant away from the head I just wanted to make sure. As I did think the log could of been exclusive to the cold start valve as it was bolted to it. No problem though. I've been told for quite some time to get rid of the cold start valve as it is an ancient technology and now i have the link I can do just that

[sneakey pete]

Plenty of people are able to get rid of the cold start valve and use the factory stepper motor for cold as start control on an aftermarket ecu.

Probably a combo of better electronics than the 80s and the majority here not living in areas where it gets nearly as cold as Japan 

[fikemoo]

unfortunately im in the uk so its quite often cold wet and windy so a cold start is something that is needed but i wanted to get rid of that crude system, it was a thread you had posted on recently pete i believe that gave me the thumbs up for getting rid of the cold start valve especially as i have the link now, this thread was more so about the coolant that runs down the sides of the ports then in to the log under the plenum which the cold start valve is bolted to, in perticular my current greddy style intake manifold for rb25 the water ways travel quite far in to the intake manifold and after a little blast in the car i was finding my intake manifold was like radiator hot (to hot to touch) so it just gave me the idea of stopping the water from entering it, but unfortunately i cannot do this

[discopotato03]

The reason that the bypass valve is bolted to the water log is so it never cools down and closes off completely unless the engines coolant is actually cold .

The idea is that if the coolant is warm it partially closes and doesn't have the engine racing if it isn't quite cold . The system actually works quite well so unless its in the way why remove it .

 

A .

[fikemoo]

Only reason I'm removing now is because I have the link ecu. I have used the system for the past few years and I've had no issues with it. But as I have the ability now I like the idea of only have one idle control valve so to speak. Less to go wrong and just a more modern system. I thought it was quite common for people to get rid of it?

[discopotato03]

Really all the system you're talking about does is help out when the engine is stone cold or nearly . When it heats up and closes only the actual idle control valve does anything . Your call but I reckon if it aint broke don't fix it . Your alternate engine management system won't care but the standard one probably will if you ever had to refit it .

A .

 

[fikemoo]

Yeah I've been doing a fair ammount of research on what each valve does and how it does it so I can make a informed decision. Another option that has been mentioned is a vw idle control valve. A great thing is that my engine loom is being completely re made for the link so nothing is set in stone and the loom can be made for whatever route I go