Rb26 Single Turbo Coolant Routing Question

[gawdzilla]

Have a question about the coolant routing for the motor, and how it should be done on a single turbo conversion. First, a picture of how the stock style is..

The green dots are the sources of coolant. The one in the front of the motor is the small barb off the aluminum radiator neck coming off the block. The one on the intake side rear is the source by the heater feeds. The one on the exh side rear is the hole in the block. There are 3 sources of coolant, so can one of those sources be eliminated? Check the pic below for single setup...

Note how i'm trying to block the coolant source coming from the neck for a cleaner look. That hose is ugly and it seems to just Y-in with the other hose from the intake side rear.

Or do I have to run it like this?

Anyone know how the water flows around the block, or where "hot" water and "cold" water are? I assume the source by the radiator neck is the "hot"...

Those who have done it or know how the aftermarket single turbo kits (hks, greddy, etc.) are setup.. please let me know if I can eliminate the front source. thanks. A mspaint drawing would be helpful too

Edited May 21, 2007 by gawdzilla

[discopotato03]

Hi , yes RB26 heads and inlet manifolds are a bit of a sea of hoses and tubes .

If it were me I'd be trying to take water from the low point on the block and feeding it back into the system at the engines highest point which is at the top water outlet on an RB26 . The reason for doing this is that this turbo coolant system will thermosyphon coolant when the engines shut down provided the turbo itself is not a high point . Its important to realise that should there be any localised boiling going on in the engines cooling system (anywhere) gas (steam) bubbles must have an escape route otherwise the area they get trapped in gets no cooling and differences in temperature can result in cracking/warping expensive things . If the turbo or even the engines top water outlet is higher than the radiator inlet you really need to look into header tanks to avoid problems . VL RB30's had these issues and I think turbo Sierra's had a header tank into which the turbos top water outlet returned its coolant (turbo sits high on Sierra Cosworth YBD) .

Something else to think about is returning hot water post turbo into the back of the inlet manifold , I'd prefer it go direct to the radiator via the front than into the back of a relatively long inline 6 . The longevity of the engine would be more important to me than how it looks . Lastly if it decided to leak I'd rather be tracing it round the front of the head than the back .

Just my thoughts cheers A .

[s13_Skyline_inside]

hi sorry to open an old topic but im pretty curious about this as well, done a search and didnt really come up with any answers.

[Butters]

well i just posted a thread about this too but I was modifying a little more then just the turbo water lines

I am planning to take the water feed from the block then return it around the front of the engine.

Basically the opposite of what you have done in diagram # 2.

You end up without the water line around the back of the head.

Makes sense to me and its simular to how you mod the S13 water return system on the SR.

Except the rb26 already has the water nipple on the top raditator outlet pipe.

I am not sure this is the best way as everyone was a little to confused by me "ghetto" diagram.

[s13_Skyline_inside]

the only problem id see with doing it that way is that the nipple your talking about using as a feed would be at an angle against the flow of the water, and im pretty sure in a standard setup the water is suppose to flow back into the engine from there

[s13_Skyline_inside]

cmon i know some of you guys are running single turbo's on your gtr's can you share how you did your and how succesful it's been plz

[discopotato03]

No that is a water - actually THE engines water outlet to the top tank of the radiator . That front water line on an RB26 is designed to take post turbo (hot) water directly to the radiator .

The time it gets a workout is when the engine is shut down at operating temperature and its left up to the water in the turbos jackets to keep them cool enough not to bake the lube oil onto their shafts/bearings . Before I start here please DONT have hysterics because water boiling in a turbo is how its supposed to work .

When the engine shuts down oil flow stops so the bearing temperature (bearings and bearing housing) will rise - mainly heat conducted from the turbine / turbine housing and exhaust manifold/s .

IF the turbo water cooling system is designed properly it will draw coolant from lower than the turbos centres and feed it out constantly rising until it can get to the engines water outlet or header tank (eg Cosworth Sierra) . Now because RB's have the thermostat in the blocks water inlet rather that its outlet you can and should feed post turbo water to this point if at all possible - the top tank of the radiator would be better but there's no provision to do that .

Now back to the turbos , coolant in their jackets begins to boil and the resulting heat and steam bubbles rises up the outlet pipe/s and via the top water outlet and hose into the top tank of the radiator . Usually the cap is at or near the highest point and it will vent these steam bubbles to the overflow tank .

Fact : Cool water is denser and heavier than hot/boiling water , in a reservoir cool water sinks and hot water rises - heavy and light .

Heated water rises from the turbos to be replaced by cooler water - this is call thermosyphoning and its what you cooling system does when you shut the motor off . The constant thermally driven water flow generally maintains the turbos core temp at a bit over 100 C which is not going to be hot enough long enough to do any damage .

The critical thing with any cooling system is not letting steam bubbles fill an area or "trap" and displace coolant water . If you do get steam pockets you getting no localized cooling and massive temp differences with adjacent areas that do and don't have contact with the coolant . Result ? massive thermal stress and warping/cracking . People used to say that SOHC RB30's used to crack underneath the cam bearings because they have the radiator top tank lower than the engines water outlet meaning the highest point in the cooling system is not the radiator .

Out of time , cheers A .

[s13_Skyline_inside]

I understand the theory of what your saying, but the nipple on the front of the engine from the turbo is facing the wrong way for water to be flowing into the radiator, the way it's facing it would have to do about a 140 degree turn to flow the way your saying and the way the thermostat sits in the houseing also indicates that water exits the engine via the lower radiator hose, also every other car ive ever seen the coolant exits where the theromo stat is so that water circulates around the engine until its at operating temp, then the thermostat opens and lets the water travel into the radiator so it can be cooled down to keep a constant temp, please explain to me how this is suppose to happen if the water is entering the engine via the thermostat, and also where would the water go when the thermostat is closed when you first start the car in the morning, if the thermostat is closed it cant go anywhere.

[saliya]

Mine's like your bottom pic if that's any help. No kit; home-brew T04Z install.

Been running for about 1.5 years as-is; no problems.

Regards,

Saliya

[Butters]

but the nipple on the front of the engine from the turbo is facing the wrong way for water to be flowing into the radiator,

The angle of the nipple doesn't mater, the larger body of water that is flowing will determine the direction.

When a stream hits a river at 90 degree's that water doesn't alll of a sudden flow upstream, it will take a 90 degree turn and flow downstream with the rest of the river.

sits in the houseing also indicates that water exits the engine via the lower radiator hose,

Ok now your making me question the fact I think the water enters the engine at the lower hose where the thermostat is.

My reason for thinking the the lower hose is the inlet and the top hose is the outlet is as follows.

Heat rises so the lower hose is going to be coolest from the radiator.

The water pump is attached to the lower hose and I assume that the water pump sucks the water through.

if the cooling system is low ion fluid it will still work as its sucking from the lower hose, wont run dry.

Be nice for someone to confirm this.

[discopotato03]

I doubt your engine would know or care which hose (top or bottom) the thermostat regulated water flow through .

Production engines are designed to have water circulating around the system internally , thats to say the water pump doesn't need to draw water from the radiator as its sole supply .

The thermostat is only there to regulate water based on temperature to or from the radiator .

It goes like this . Earlier Nissan engines Like an L series or FJ had the thermostat at the top or water outlet so while ever the coolant was cool/cold the water pump picked up water from the blocks front jacket (timing cover actually) and pumped it through the block and up through the water passages into the head casting . At low temps the thermostat is closed so they have what I call a water pump bypass hose thats an external steel pipe and is connected to the back of the head and usually the lower part of the thermostats reservoir area . This pipe/hose is probably 19mm and feeds directly back into the pump on FJ's anyway . Where the pipe is plumbed into the back of the head rubber hoses generally duck through the fire wall to sent water from the head to the cars heater core . The return feeds post heater water to the rear of this water pump bypass hose . From this you can see that the engines coolant can do the roundies oblivious to the radiator or its hoses . When the coolant reaches a set temperature the thermostat starts to open and feed hot water to the top of the radiator which until this point is full of cold water . Cold water can then start to flow from the bottom tank of the radiator to the engines water inlet generally in the vicinity of the water pump .

I can hear some of you thinking why does water flow through the thermostat/hose/rad/hose if this water pump thingy is there ? Very simply the fully open thermostat/hoses/rad pumbing is larger/higher flowing than the bypass plumbing and water like most things will take the least path of resistance .

Back to RB's and the like with thermostats on the block side of the lower rad hose . If water cant flow beyond the bottom of a radiator then it can't get in the top can it ? Trust me water isn't compressible so a rad can't take in more than it can let out . Warm up process , engine heats up as per normal except that because the top water outlet and hose are in permanent communication with the radiator the water in the top tank will be at the same temperature as the water in the heads water jacket . With the thermostat down low on the block at the engines inlet virtually all of the water in the block has to reach the thermostats opening temperature before it will . Also this time round its letting post rad water into the block and pump not hottest water at the top outlet back into the top of the radiator .

The RB26's post turbo water fitting is a manufacturing convienence more than anything , I doubt water from an ~ 8mm hose is going to fight its way through the flow from a what 34mm duct ? and get anywhere near the head .

Before I finish - if you can source turbo water from a very low point on the bolck and feed it back into the system just beyond the main engine outlet the engine never sees (feels) heat from the turbo/s . Some people feel the need to pump water through the turbos but the thing is there is no pump driven flow once the engine stops and thats the critical time for a turbo coolant system . The bottom line is if it can't thermosiphon and the turbo/s boil off their jacket water then the system has achieve zip . It MUST be able to operate totally indipendantly or it may as well not be there at all .

Cheers .

[s13_Skyline_inside]

makes sense, ive tryed to find some nissan diagrams to show which way the water flows but to no availe so i might just rout it the way the bottom pic is done as that is pretty much the way nissan intended it to be which im sure they didnt just do for the sake of doing it . its just ive seen some pics of engine bays that dont have the front nipple connected, but yeh 1 thing that didnt really make sense to me if the water flowed the way i thought it did is why would you have hot water running back intot he engine.

[s13_Skyline_inside]

just to clear up the way the water flows just run the car for a bit and see which hose is hotter, top/bottom then you'll know which way the water flows, obviously the hotter hose will be post engine, unfortunatly im not in aus at the moment so i cant get to my car to figure it out for myself

[SirRacer]

Is this any different at all for an rb25.

Can cubes or one of the GT series rb25de head guys post up where they have fed they water return into

Thanks

Byron

[s13_Skyline_inside]

the return would be back into the block where it is standard, so yeh same as with the 25, what i was wondering is if its possible to just run the system without the part of the line that goes around the front of the engine?

[Shaun]

I did mine a few years ago, so its hard to remember, but i definately blocked off the front water in/outlet and used the one out of the block and the one at the back of the plenum.

Shaun.

[Shaun]

I did mine a few years ago, so its hard to remember, but i definately blocked off the front water in/outlet and used the one out of the block and the one at the back of the plenum.

Shaun.

Here are some pics for those interested:

It might look a bit cumbersome to some, but i wanted to leave a significant air gap between the lines and the (ceramic coated) manifold. Also, i had to silver solder a 'weld on' to the water pipe behind the plunum.

Shaun.

Also, i just went and read through my manual, and it said that the hot water flows into the bottom of the radiator. Also, the water temp sensor is on the top radiator hose, so this would suggest that this is cooler water.

Edited December 1, 2007 by Shaun

[s13_Skyline_inside]

cool thanks, hehe i actually saved the pic in your avatar a while ago so i could zoom in to see what was going on .

thats the way i want to run mine, so yours has been fine no problems with it? btw looks fkin neat

[SirRacer]

Hey Shaun,

do you have any pictures of where the water return goes into on the other side?

Thanks

Byron

[Shaun]

cool thanks, hehe i actually saved the pic in your avatar a while ago so i could zoom in to see what was going on .

thats the way i want to run mine, so yours has been fine no problems with it? btw looks fkin neat

Well, i wouldnt say its been going fine; it blew a head gasket on the dyno resulting in a full rebuild (its a long story). Thats why its apart at the moment. But there were no overheating issues at all while it was going. I researched it thoroughly when i was pulling the twins off because i was unsure like you. When i first started it, i used an infared temp gauge on various parts of the head and block and found no massive temp fluctuations.

As for a picture of the other side of the engine, i dont have one that shows it all assembled. There is an assembly of solid pipes under the plenum. I think there are two small ones (these are vacuum pipes) attached to one larger (water) pipe. The water pipe is connected from the thermostat part of the block to one of the heater hoses that goes around the back of the engine. Just before it connects to the heater hose, there is a junction that i cut off and attached a weld on to so i can use an Earls fitting. The picture below shows the general area of the connection.

I do sometimes wonder, however, if it would have been better to bring the cooler water from the front of the engine (top rad' hose) to the turbo, and then run it around the back of the engine. I dont know if taking it from the block on the exhaust side is as effective. Id like to heat some experienced views.

Shaun.