240z overheating at idle in traffic lights and intersections

[Stanley]

He's got the little NLA manifold heater thermostat. You can see it in the second photo posted in this thread, on the rear intake manifold. Whether it works or not is another question. It's probably a good idea to have it in the system. Maybe I'll get one  someday, but it's way down on my list. Problem is the tube that goes through the manifold rusts out and leaks (mine was totally shot), no easy way to fix it then. Doubt if it's necessary in Panama.

FSM says (about) 3.3 to 4.3 psi is acceptable range. I get 3.9 to 4.0 psi with stock mechanical pump and no return line. No problems. No telling what his aftermarket electric F.P. puts out without testing it, though.

1/4 turn of the mix nuts can make a big difference.

Edited January 9, 2016 by Stanley

[Zed Head]

The thing I circled?  It shows up in the pre June 1972 diagram.  Looks a lot smaller though.   #38

http://www.carpartsmanual.com/datsun/Z-1969-1978/engine-240z-260z/manifold/to-jun-72

[Stanley]

Yep.

[Zed Head]

Found this today.  Posted the larger picture in a different thread.  Page EC-21 1972.  Percolation is a bad thing, I think.

[jalexquijano]

On ‎01‎/‎09‎/‎2016 at 1:55 PM, Zed Head said:

Found this today.  Posted the larger picture in a different thread.  Page EC-21 1972.  Percolation is a bad thing, I think.

OK. I have already checked my mixtures and have set the front carb to 4 turns clockwise and the rear car to 3.25 turns clockwise. My starting point was 2.5 each carb as the DVD shows but at that point the fuel mixture was too lean. Anyway, i took the car for a ride and drove it approximately 20 minutes stopping at intersections and several traffic lights, trying to keep the temperature needle under half. Car is running with no thermostat on. Anyway, once it passes half  the idle becomes rough and it tends to stall which is not pleasing at all. The problem is not the carbs believe! Have set the BTDC to 11 although i am planning to increase it to 13 to see if the car has more power at 1st gear. when i came back i took the plugs out and they all showed as attached. I also took some pictures of the manifold heat control thermostat, carb shields and other parts so you can guide me better on the solution. Formerly i had the original heater installed, nowadays i manage to install an ac system from vintage air and bypassed those heater lines. im about to ditch that radiator and remove the freeze plugs as any passages could be blocked.

[siteunseen]

Are you turning the mixture knobs CLOCKWISE until they are tight, towards the passenger's side?  Then turning them COUNTERCLOCKWISE to loosen or lower them 2.5 turns, towards the driver's side, and they are too lean?  So then you are turning them another complete turn COUNTERCLOCKWISE, towards the driver's side to richen them?

The plug looks good enough to me considering they were black previously.  Your number of turns seems to be too rich and I'm trying to understand why.

Could you go to a auto parts store and borrow a vacuum gauge to get a reading?  That would be useful information whether or not your engine has good vacuum or is worn.  17hgs on the gauge is good, less could be a clue as to your problems.

The 2 hoses coming out of the firewall by the battery are being used for your air conditioner's compressor, right?  That could only mean the coolant route has been changed, good or bad I don't know but the pictures are a big help.  Maybe somebody will see something?   

[jalexquijano]

Sorry i meant Clockwise until they are tight, and then 4 turns counterclockwise the front carb and 3.25 turns counter clockwise the rear carb (loosen or lowering the jet. I have a vacuum gauge at home. You will only need to tell how and to which port i must connect it to measure the vacuum. 2 hoses coming from firewall are used by the sanden 508 compressor. Coolant route has been rerouted. Anyway, if i dont manage to find a Manifold Heat Control Thermostat can i simply remove it or it can be fixed if it is shut???

[siteunseen]

Mine was removed by the previous owner and my car ran great, maybe used a longer choke time in the colder months but hardly any choke at all in the warmer months.  My understanding of that coolant line through the intake manifold was for extra heat for colder weather, about 2 months here in Alabama, probably never in Panama.  There's an active thread going on now about that thermostat but those guys live way up in Canada where it's cold, really cold. 

For a vacuum test, if you have the right adapter (big) use the brake hose bung.

 

 

[jalexquijano]

In conclusión do i remove the Manifold heat thermostat or purchase one from you guys to replace the probably shut device? Temperature in Panama is 33 degrees Celsius all year round.

Edited January 12, 2016 by jalexquijano

[Namerow]

The Manifold heat thermostat functions so that it's open when the engine is cold and closed when the engine is warmed up.  If your Manifold thermostat is stuck (mine was), it's almost certainly going to be stuck in the 'open' position, which means two things:

1. Your manifolds and carbs are probably being treated to heated coolant all the time (including when you're sitting at stop lights in 33-degree weather with a hot engine)
    
2. Removing the Manifold thermostat from the circuit won't make any difference, because the thermostat was already stuck in the 'open' position.

Removing the Manifold thermostat from the circuit and then blocking the circuit with a plug may not be a good solution either.  There are concerns (although not confirmed) that this might create undesirable side-effects in the operation of the regular sections of the engine cooling system.

I suggest that you remove the Manifold thermostat and check it to see if it is, indeed, stuck 'open'.  Use the test procedure from the FSM (see my other thread for details).

If this test shows that your Manifold thermostat is stuck in the 'open' position, you can probably get it working again by soaking it overnight in a jar of 'C-L-R' (chemical used for 'de-liming' electric kettles and other home appliances).  You can also try carefully heating it (actually, over-heating it) with a small butane torch to see if you can get it to close.  Again, see my other thread for more details.

[Jarvo2]

I know you're running round-tops, but the concepts within this Fuel System Modification guide may prove useful as well in your current situation.

Fuel-1973 240z 1974 260z fuel system modifications.pdf

[Zed Head]

4 hours ago, Jarvo2 said:

I know you're running round-tops, but the concepts within this Fuel System Modification guide may prove useful as well in your current situation.

Fuel-1973 240z 1974 260z fuel system modifications.pdf

Cool document.  If you don't add it to the Downloads area I probably will in a few days.