Rear Cylinder Coolant Bypass Modification
06-07-2006, 08:28 AM
#1
Rear Cylinder Coolant Bypass Modification
First off, I wish I could take credit for figuring this out, but Doug at Crawford Z Car deserves the credit for noticing this modification. Recently, he was doing some work on a Nissan Pathfinder with the VQ35, and discovered that the VQ35 block already has provisions for extra rear cylinder cooling. Nissan uses this setup on vehicles that might experience heavy towing loads.
Well, remember that block off plate in the center/rear of the VQ35? One vendor made a product to help fill the cooling system from this passage. But in reality, it is designed to accept a secondary thermostat, housing, and piping, which allows coolant to flow out of this passage, and back to the cast cooling pipe.
Pictures are worth a thousand words. The secondary thermostat opens at 195F. These are pictures of my engine, with the modification completed. I tested this on the dyno. Keep in mind, with Darton sleeves, baseline coolant temps hover around 195F, vs. 185F with the factory open deck. After repeated dyno pulls, my coolant temps never exceeded 203F!! You will recall, that my coolant temps on the dyno used to exceed 215F after repeated pulls, and others have reported even higher temps.
All of the parts needed are OEM Nissan Pathfinder parts. You do have to cut the passenger side hard coolant pipe, and eliminate the o-ring connection. You may need to weld shut, a couple of your coolant bypass opening as well, on both the driver and passenger side hard coolant pipes. But that's about it...everything else just bolts on. And we did try installing the Pathfinder waterpump, but its a different gear and configuration, and will not fit onto the 350Z/G35 timing plate or chain.
After seeing so many people have issues with overheating, I felt it would be best to share this with everyone; competitors included. Hopefully this simple and relatively inexpensive mod will help prevent expensive engine damage. We'll be using this on all the forged motors we install.
Well, remember that block off plate in the center/rear of the VQ35? One vendor made a product to help fill the cooling system from this passage. But in reality, it is designed to accept a secondary thermostat, housing, and piping, which allows coolant to flow out of this passage, and back to the cast cooling pipe.
Pictures are worth a thousand words. The secondary thermostat opens at 195F. These are pictures of my engine, with the modification completed. I tested this on the dyno. Keep in mind, with Darton sleeves, baseline coolant temps hover around 195F, vs. 185F with the factory open deck. After repeated dyno pulls, my coolant temps never exceeded 203F!! You will recall, that my coolant temps on the dyno used to exceed 215F after repeated pulls, and others have reported even higher temps.
All of the parts needed are OEM Nissan Pathfinder parts. You do have to cut the passenger side hard coolant pipe, and eliminate the o-ring connection. You may need to weld shut, a couple of your coolant bypass opening as well, on both the driver and passenger side hard coolant pipes. But that's about it...everything else just bolts on. And we did try installing the Pathfinder waterpump, but its a different gear and configuration, and will not fit onto the 350Z/G35 timing plate or chain.
After seeing so many people have issues with overheating, I felt it would be best to share this with everyone; competitors included. Hopefully this simple and relatively inexpensive mod will help prevent expensive engine damage. We'll be using this on all the forged motors we install.
Last edited by Sharif@Forged; 06-07-2006 at 08:31 AM.
06-07-2006, 09:03 AM
#7
Originally Posted by ZU L8R
Do you have a list of what you need
We sell the prepackaged kits for $250 shipped. You might be able to order them for less direct from Nissan, but there a bunch of little parts that you'll have to dig up. Bolts, gaskets, clamps, the housing, thermostat, hard coolant pipe, and hoses.
Trending Topics
06-07-2006, 09:20 AM
#8
Registered User
iTrader: (2)
Join Date: Oct 2005
Location: Houma, LA
Posts: 171
Likes: 0
Received 0 Likes
on
0 Posts
I'll have to cut and rotate the hard pipe that goes around the passenger side.. since our engine will be in a FWD car..I'll just rotate it around, and reweld it. The VQ30DE-K FWD engine has a coolant line running to that spot in the block as well.
Travis
Travis
This is a must mod - great job Sahrif!
06-07-2006, 01:03 PM
#12
Registered User
iTrader: (4)
Join Date: Mar 2005
Location: EveryWhere & yet... NoWhere
Posts: 2,880
Likes: 0
Received 3 Likes
on
3 Posts
Sharif, Doug:
Thanks again for all of the hard work you guys put into finding solutions for making these VQ35 blocks more resilient.
Even more, thanks for sharing this knowledge with everyone so we can all benefit and continue to see where these blocks can take us.
--B
Thanks again for all of the hard work you guys put into finding solutions for making these VQ35 blocks more resilient.
Even more, thanks for sharing this knowledge with everyone so we can all benefit and continue to see where these blocks can take us.
--B
06-07-2006, 07:27 PM
#19
thanks for sharing sharif. now i'm trying to figure out how it would actually cool the rear cylinders though. the only thing i have come up with is that it may increase water flow through the water channels in the block around the cylinders. but right where the water passages are that feed that opening, is where the head gaskets open up and the water from the block gets reintroduced to the heads and goes into that rear manifold anyways. it must drop the pressure and create more flow around the cylinders the way you have it now.
curious also why they have a thermostat there? maybe more flow is to be had with it removed. the dia. of the tubing is saying it should flow like a mother anyways though. possibly a bubble tank running inline on the out rubber line (if extended ofcourse) sitting high on the rear firewall would be magical.
maybe i am over thinkin this, sorry been long day.
curious also why they have a thermostat there? maybe more flow is to be had with it removed. the dia. of the tubing is saying it should flow like a mother anyways though. possibly a bubble tank running inline on the out rubber line (if extended ofcourse) sitting high on the rear firewall would be magical.
maybe i am over thinkin this, sorry been long day.