Hello everyone.

As these engines get swapped more often I would like to explore some of the options to "simplify" the cooling system. Already running a TB coolant bypass.

I've seen some folks bypass the heater by running a hose from the engine's heater outlet to inlet.

It appears like in these engines the heater is usually seeing flow (certain cars bring a flow valve to stop coolant flow through the heater). It seems like anything 2000 + Nissan/Infiniti does not.

I'm sure the vent doors block airflow, however the heater must allow a few degrees of cooling it still sees hot coolant being sent back into the Tstat area.

With that being said, the Tstat already receives a hot feed for opening already from the back neck.

I have the heater pipes capped and so far can report normal function however makes me question if a bypass over capping would offer any benefits in cooling or such?

My theory is the heater pipe by the T Stat shares the channel of the second hose. By bypassing the heater you're sending hotter than the return coolant back into the bottom of the block.

Seem like my theory was correct. Bypassing the heater and not capping the pipes will send hot coolant to the bottom part of the block to blend with colder coolant.

In the oem configuration, having the heater will lead to a cooler effect even if there is no air flow going through it.

As you can see the inside cavity of the thermostat where the hoses go are only divided by a small piece of aluminum, this is so the heater change in temp doesnt affect thermostat operation. These cars do not bring a heater flow valve meaning coolant is constantly running through the core and it's the blend doors job to block airflow so you dont get hot air.

Time will tell however I wonder for those experiencing high coolant temps while racing if they'll see a significant improvement in coolant temps by shutting flow to the heater all together.

 

Totally worthwhile cleanup!
Vacuum lines could use some help too.

Don't see the oil filter "cooler" lines in the above diagram.
But I think it's part of the throttle body coolant line circuit.
I too ditched those lines by looping the rubber line back into the hard line manifold on the driver's side of the block.
And bypassed the heater core lines with a looped line.
Left the burp fitting in the loop.
​​​​​​ Cabin temps dropped by 15 degrees without the AC running.
but the stereo stack sure makes a lot of heat all by itself.
Also installed a brass water heater ball valve in the heater core bypass loop.
Didn't see a difference in coolant temp with it open or closed, But this was only during daily driving in the Florida summer. Not a track day

​​​​​ other other modifications to my coolant system are...
CSF manual radiator with
divorced 15 row trans cooler.
15 row oil cooler.
Bigger PS cooler.
Somehow I squeezed an intercooler and supercharger cooler up front as well, but that's a different story.
​​​​​
Oh yeah, ceramic coated long tube headers keep my right leg slightly less toasty than the uncoated stock headers and test pipes, and I'm sure are way cooler than having the cats right there.

 

Vacuum lines are purposely there for blowby monitoring, I switched the PCV to flow into the evap vacuum sources since I dont have Evap (cleans up the front part of the engine)

The diagram is for G37s without oil cooler/warmer, this cooler/warmer ends up being paper weight when you go external oil cooler and its deletion plays no effect into cooling being that VHRs already came without them.

Im happy to hear cabin temps dropped which confirms the theory of the heater core ALWAYS seeing hot coolant, it also explains the stupid heat radiance in the cabin that you feel with fresh air, thanks for that.

The ball valve is a pretty interesting approach at this experiment since it lets you try it both ways. I suspect that since the capping did not affect anything neither would a block however was expecting some differences in possibly fan cycling or definitely racing times


Thanks for taking the time to experiment and also reply.