Intake manifold (L20b) coolant passage cap ?

[Sh00bs]

got away from the hitachi for a weber 32/36 and it's AWESOME. feels like a new engine tbh 
at the same time i deleted all the SMOG junk in my bay since it's a california truck (now in Maryland). 
I deleted the coolant line that went from the intake manifold in front of the engine, tapped into the thermostat housing and then down to the lower main coolant line into the block. 

however that cap popped over the weekend and pissed coolant everywhere, too much pressure from having fun with my new more performance carb lol

can anyone recommend a better cap or what i should cap with ? 
oorrrr
should i just put a line back in and route it into the lower main line on the left of the block ? 

[datzenmike]

The by pass is important. Without it the water around the thermostat is stagnant and doesn't move. While the engine warms up the thermostat does so only slowly by convection and lags behind what is going on inside the engine. The engine can and will over heat internally, even generate pressure and the rad hoses become hard, but the thermostat remains closed. This only happens until the thermostat finally opens then it self regulates. The by pass allows a small amount of flow past the thermostat from inside the head so it can sample it and react faster to the actual engine temperature.

 

The coolant lines inside the intake that connect to the by pass are also important. Gas does not burn unless fully evaporated and to do this it absorbs heat from the carburetor, intake port in the head, the intake valve and the hot combustion chamber. The coolant warms the intake when the engine or the weather is cool and the engine is much faster to warm up, and runs smoother. In extremely hot weather the coolant absorbs the radiant heat from the very hot exhaust manifold just an inch away. The coolant in the runners manages to keep the air in a more temperate range than if it was without. Lastly, the coolant on the middle and rear of the head has a long way to go to get to the front and out the thermostat housing. The coolant has two escape points into the intake runners and this promotes circulation of fresh coolant up from the block and prevents the head being hotter at the rear than the front.

 

Yes, keep the by pass functional. Nissan didn't do this for no reason at all. It's well thought out

[RyanC]

Hey I'm new here first post but picked up a 1500 Truck (620) last month and it doesn't seem to have the pipe to connect to the thermostate for the bypass.  I can run the bypass from the block inlet round to the inlet manifold (32/36 Weber).  Should I hunt down the lower thermostat part with the  connector?  Actually I think it has some points that look like screw in taps that are blocked off.  Will have another look.

 

Sorry for the Hijack 🙂

 

Will organise my own build thread soon.

 

Ryan

[datzenmike]

1500?? would that be a J15? Check the thermostat itself. It may already have a 'jiggle' valve in it. You can also drill a 1/8" hole which will do the same thing. The jiggle valve is a small leak that promotes coolant circulation through the thermostat.

 

 

 

If the thermostat is mounted vertically the hole must be at the top like this one, but if horizontal it doesn't matter. I would prefer a proper coolant by pass but this will work.

[RyanC]

It was a J15 but the previous owner swapped it for the l20 and floor 4 speed. I'll have a look at the thermostat I feel like 20 years ago my last l20b had that sort of valve in it.

 

I can run the hose to the intake under the Webber as  all the connections points are there just none at the thermostat.

 

Thanks

[datzenmike]

If L series then thermostat is horizontal. I think only the earlier L16s didn't have the by pass hose and only the jiggle valve. By connecting the thermostat housing to the line from the intake the partially warmed water goes directly back into the engine. With a jiggle valve it goes to the rad and an equal amount of cold water goes into the engine slowing the warm up on really cold days.

[RyanC]

I think I'll pop a hole in the thermostat to allow some flow and run the bypass direct to the inlet manifold as that appears to be all there.

 

Only below freezing here a few times a year here.  Thanks for the help.  I'm pretty sure my 510 (1600) had the jiggle valve and I rehomed onto my l20 when we built it. 25 years ago almost.