water cooled manifold

Jimbo

1978 260z in yellow
Club Member
can anyone shed any light on why the manifold on my 78 260z is water cooled and if i can delete the water cooled function by simply blanking off the coolant connections at the thermostat housing and the T piece on the other side of the block?


thermostat outlet


sparkplug side of block Tpiece.



my carbs have been playing up due to throttle spindle wear, so i have bought some genuine new/old stock SU carbs that arent water-cooled, hence me wanting to block the passage of coolant through the manifold by blanking the outlets from the thermostat housing and tpeice on the other side of the block.
 

Jimbo

1978 260z in yellow
Club Member
yes please.
i assumed its to help prevent carb icing in the cold winter months
 

SeanDezart

Well-Known Forum User
i assumed its to help prevent carb icing in the cold winter months
Why would water-cooling prevent icing ?:confused:

It's to prevent fuel evaporation and present because the Z was a world-car, sold into many different markets with widely different climate.....most European temperate climates don't need it and there are other after-market ways to prevent it that were too expensive as a factory-build option at the time.......therefore you can lose it and IF you need to, replace it with other, more effective solutions.
 

Rob Gaskin

Treasurer
Staff member
Site Administrator
Why would water-cooling prevent icing ?:confused:

......

I always thought it was a water heated manifold but I suppose it's both.

If the pipes are ok I'd leave it connected but the problem most people have is that the pipe is blocked or rusted through.
 

SeanDezart

Well-Known Forum User
.....but the problem most people have is that the pipe is blocked or rusted through.

What I've heard of most is that non-stock parts* conflict with the pipe which then must be modified/isolated.

*including triple carb inlet and especially exhaust manifolds.
 

Rob Gaskin

Treasurer
Staff member
Site Administrator
What I've heard of most is that non-stock parts* conflict with the pipe which then must be modified/isolated.

*including triple carb inlet and especially exhaust manifolds.

On my old car Sean with the standard the pipe was solid with 'crud' (lovely word) and when I looked at it closely it had numerous small holes too! So I ran without it connected - no problem here.
 

SeanDezart

Well-Known Forum User
'crud' is a lovely slang term here for dirty, an adjective as opposed to a nown.

eg that car was crud inside !
 

Jimbo

1978 260z in yellow
Club Member
the reason i wanted to block it off is because I've obtained a pair of new SU carbs but they aren't water cooled so require the water system blanking off.
my old carbs have bad air leaks around the throttle spindles so unless i can get the bodies rebushed the SUs will be the alternative.
 

Jimbo

1978 260z in yellow
Club Member
thankyou all for your help so far.
my next question is do i need to bleed the cooling system now i have blanked off and refilled the cooling system?
and if so, how do you bleed the cooling system?
 

MaximG

Well-Known Forum User
So ok it's a fairly straight forward job.

Take the radiator cap off.
If needs be top up the coolant.
Turn the engine on and let it run upto temperature.
Keep an eye on the coolant level because your waiting for the thermostat to open.
Be aware when it does the air pushing past the thermostat and being driven by the pump may push some water out the radiator.
So keep an eye on the level when the thermostat has opened the level will drop in the radiator. Top up with more coolant and put the cap on.
Job done.
 

Rob Gaskin

Treasurer
Staff member
Site Administrator
the reason i wanted to block it off is because I've obtained a pair of new SU carbs but they aren't water cooled .......

I don't understand this, do you mean carbs on a manifold or just 2 carbs? The carbs aren't watercooled the manifold is.

thankyou all for your help so far.
my next question is do i need to bleed the cooling system now i have blanked off and refilled the cooling system?
and if so, how do you bleed the cooling system?

I would just check the coolant level cold - it needs to be about an inch from the top to allow for expansion.
Replace the cap and check after using the car when cold. It should just bleed iteself - unlike some modern cars.

I don't like running the car hot without the cap on.
 

A2Z

Well-Known Forum User
1978 260Z Carburettors

The carbs aren't watercooled the manifold is.

Here is a picture of a Hitachi "flat top". Not sure if it is for a 1978, but I always thought the pipes in the base were to route water through the carburettor body.
 

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MaximG

Well-Known Forum User
It should just bleed itself.

Until the thermostat has opened any air behind it wont go anywhere. The system unlike modern cars does not run at high enough pressure to force the air to saturate into the water.

So until its been run up to temp the thermostat wont open and let the air out.

To be honest I do take some offence in the insinuation that I'm wrong Rob. Like your boys I have a Dad that spent all his life working on Cars he was even an apprentice mechanic when apprenticeship meant something. Its the way my brother and I were taught and you know what, cant say its ever been a problem!
 

MaximG

Well-Known Forum User
I don't understand this, do you mean carbs on a manifold or just 2 carbs? The carbs aren't watercooled.

The Hitachi carbs have a gallery underneath them that was part of the water cooling system. I you took one off today you would more than likely find it clogged up with crud.
 

Rob Gaskin

Treasurer
Staff member
Site Administrator
Until the thermostat has opened any air behind it wont go anywhere. The system unlike modern cars does not run at high enough pressure to force the air to saturate into the water.

So until its been run up to temp the thermostat wont open and let the air out.

To be honest I do take some offence in the insinuation that I'm wrong Rob. Like your boys I have a Dad that spent all his life working on Cars he was even an apprentice mechanic when apprenticeship meant something. Its the way my brother and I were taught and you know what, cant say its ever been a problem!

Mike, I'm saying I wouldn't do it your way, you can. I had a dodgy thermostat on my orange car so I did what you did to see if and when it opened. When it opened very hot water came OUT of the rad violently, I was shocked and felt daft for even trying it. When rallying in the 70s someone working on our Avenger scalded himself badly by opening the cap when the car was hot.

So my experiences may be isolated but they don't put warnings on rad caps for nothing.
 

Rob Gaskin

Treasurer
Staff member
Site Administrator
Here is a picture of a Hitachi "flat top". Not sure if it is for a 1978, but I always thought the pipes in the base were to route water through the carburettor body.

The Hitachi carbs have a gallery underneath them that was part of the water cooling system. I you took one off today you would more than likely find it clogged up with crud.

Well 'hands-up' guys I've learnt something today - every day is a school day. It's obvious to me that the flat-tops are watercooled/heated because the have pipes on them but I never realised that the 240Z carbs were. I've only had SUs on my old car and they weren't.

So the holes in the spacer/insulator at the bottom are to supply water? I didn't have those holes on my spacer and I've never taken the carbs off my current cars (Hitachi). So when the carbs are removed a drop of coolant runs out?

Thanks guys.
 
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