water jacket plumbing carb'd L28

[jalien]

Hi all! so, we've installed a pair of su hs6's and they're soo much better than the dual 32/36 webers he had on. anyway, whatever carbs we had on, we noticed a difference whether we had water going into the water jackets or not. we noticed plumbed up is better for consistency and cold starts, but we noticed a bump in operating temp. without the water jackets, operating temp was from 190 to 195 depending on driving. with water going through the jackets, operating temp is 193 to 205 depending on driving. the way we have it plumbed is from the lower inlet to the rear carb to the front carb to the t-stat. is this right?

 

 note: no heat shield and heater core.

 

is the heat from the exhaust manifold heating up the water too much without a heat shield?

 

thanks in advance for answers!

 

 

[datzenmike]

You either have the much earlier SU intakes of the 240z or a custom one. If the 240z intakes, only the throttle chambers are warmed by coolant and there is no flow out of the head itself or through the intake runners. You have it connected properly but the coolant flows from the thermostat housing back to the front manifold just behind the SU, then to and through the rear intake manifold again just behind the SU and out the rear side around the back of the head and is connected to the lower radiator hose inlet to the suction side of the water pump.

 

It should be noted that this hot water from the thermostat is being directed back into the water pump inlet at the lower radiator hose without the benefit of passing through the radiator and being cooled. Effectively you are by passing hot coolant past the radiator increasing it's work load on the coolant that does. I would not doubt that the engine will run slightly warmer with this system connected. Possibly the 240z system has a restriction in the return line to limit the flow? Maybe a shut off valve for very warm weather when the warming of the throttle chambers are not needed? Have it operational during cold weather. Or adjust the flow so the temperature does not rise?

 

 

 

 

 

 

 

[jalien]

thanks! dang, i messed up. the plumbing is for the water jackets in the intake manifolds, not the carbs. my bad.... but still same scenario. what u stated is what i was pondering.. that the water is not being circulated. do u think 205f is too high? i read a few places that 215 is too hot. thanks

[ggzilla]

On 3/31/2025 at 2:03 PM, jalien said:

do u think 205f is too high?

205 is not too high. You want the engine coolant temp to be above 180 for optimum oil operation

But below boiling point (212, or with a radiator pressure cap about 230)

Below 190 is better to reduce the chance of detonation on the old open chamber head designs

Coolant in the manifold is below runners, so doesn't negatively affect airflow like hot air intake does, but instead aids in proper atomization for more power. The cold climate thing comes into play with the air temp and is why the twin carb air cleaner had a hot air tube to prevent carb icing during winter

 

215 in the intake manifold sounds high. Maybe the outlet is blocked

Datsun 220 manifold has an outlet at the front end and inlet at the cylinder head face

 

 

Datsun K14 manifold has water connections on both(?) ends of manifold. Not sure how that one is plumbed

[datzenmike]

It's an L28 with presumably an after market dual 32/36 weber and then presumably switched to a 240z intake with SUs.

 

Get an infra red heat gun and shoot the thermostat housing to get a realistic temperature reading. I don't trust gauges till they are confirmed good. While it will run at over 200F it may ping under load and performance will be hampered. I would prefer under 190F.

 

If those numbers are correct replace the thermostat.

[ggzilla]

thanks, i read as carbd L18

 

Using an external thermometer is a great idea. I have a little battery-powered laser temp gun and it is suprisingly accurate. And lets you get spot reading of very specific parts of the engine