Head cooling on cylinder #5 - solutions?

[RTz]

Bob, You have a PM

[Z_Maggio]

Forcedfed Z...One more thing.When hot (1220+)exhaust gases leak into the cooling system,the temp will spike very quickly.I suggest a Nissan head gasket and ARP head studs and make real sure the two surfaces are flat and clean before assembly. Bob

[Tony D]

Lifting the head is not really an issue with Nissan Heads like it is with Ford 5.0's.

more likely it's a partial failure of the head gasket under boost.

 

On the subject of 'when is it appropriate' I think it goes more towards what BMEP the engine is designed to operate at full time. The stresses of a stock turbocharged L-Engine is still below what the FIA engines were running in the early 70's, and those engines got a special non-crossflow head that had more of the 4 Cylinder L-Head arrangement for evacuating coolant from the head with large chambers between cyls 1/2, 3/4, 5/6 to a separate manifold that went to the radiator.

 

Same goes for the LY Crossflow head which took coolant off the head above the cylinders in pairs similarly to the FIA head, and ran it out to the radiator in a hose-sized manifold which contained the thermostat (it was not on the bolt-on casting on the side of the head).

 

I believe Nissan recognised that below a given specific output, the L-Head was totally acceptable in it's cooling characteristics, but permanently turn up the wick some more (325HP on the L24...) on an expected full-time horspower expected operation, and the cooling was not so great and so they changed it in purpose built parts specifically designed for that purpose.

[Forcefed Z]

Forcedfed Z...With that nuch power,you must be running pretty high boost.You may be lifting the head off the block.Are you running head bolts or studs?To pressurize the cooling system,compression has to be "leaking"into the cooling system.That can only be a bad gasket,crack in the block or head.

Maybe I'm just a lucky guy but I roadraced a 2.8na(300hp)12.8 to 1 compression ratio with none of these problems described here.In road racing,the races were 30-45 min and I routinely shifted at 7800-8000rpm.I also had a z car shop in New Orleans for 25 years.Maybe I'll learn something new here.Thanks,Bob

 

I have arp's and a 2mm nissan comp gasket, running 25 psi last time if I remember right, turned it up higher but didnt make much more power....if I recall it was 28 mabe more for the 480whp run.....Originally I thaught the head had cracked, as it was cracked before...I had a low k motor and took the head from that and ported it got new arp's new gasket......same happened.....changed the rad for a big aluminum one.....same happened....but keep in mind ive never driven the car with less boost till recently.....now at 15psi about 350 whp it isnt as bad but is still blowing out coolant......

[Z_Maggio]

"O" ring the block

[WizardBlack]

Just as an update, I added two cooling circuits as suggested here. There is a -6 AN line from the number five jacket to the water pump inlet neck (to facilitate lots of water flow) and another -6 AN line from the number six jacket to the thermostat housing (for lesser flow and to avoid having two circuits recirculated back to the pump inlet). I kind of mirrored ktm's setup, I suppose. At the same time, I also went from 50/50 water/EG with water wetter to 85/15 water/EG with water wetter. I noticed that sitting still it would be down in the 160's but eventually creep to 190, but running around it stays solid or even a tad low. It stays at about 178~181 *F in full power pulls and cruising along will sit around 167'ish. I will try to take more notes on the heat levels and post pics of my install (if anyone is curious). I am using a new standard water pump and have dual electric cooling fans. I also ported and cleaned up the oil and water circuits in the timing cover. The water outlet (to the block) had a lot of room for improvement.

[hughdogz]

If I run the coolant hoses into the UPPER thermostat housing, will that work? I figure it is equivalent to running directly into the radiator inlet.

 

From the looks of RossMan's diagram, he's planning on running into the lower thermostat housing?

 

Thanks! -Hugh

[TimZ]

If I run the coolant hoses into the UPPER thermostat housing, will that work? I figure it is equivalent to running directly into the radiator inlet.

 

From the looks of RossMan's diagram, he's planning on running into the lower thermostat housing?

 

Thanks! -Hugh

 

If I'm interpreting your question correctly, running into the upper housing would bypass the thermostat, which would most likely make your water temps swing more widely.

[ktm]

If I'm interpreting your question correctly, running into the upper housing would bypass the thermostat, which would most likely make your water temps swing more widely.

 

Swing widely? I don't think swing is the correct word. Once the t-stat is open, then running a line to the upper housing would not be any different. Running it to the upper t-stat housing would be like running without a thermostat at all. It would take longer for the car to get up to operating temperature. Once the car is at operating temperature, the t-stat is open though not all the way (depending on the temperature rating of the thermostat).

[TimZ]

Swing widely? I don't think swing is the correct word. Once the t-stat is open, then running a line to the upper housing would not be any different. Running it to the upper t-stat housing would be like running without a thermostat at all. It would take longer for the car to get up to operating temperature. Once the car is at operating temperature, the t-stat is open though not all the way (depending on the temperature rating of the thermostat).

 

I was trying to be polite.

 

What I was trying to point out was that the coolant temps would drop much farther in low heat load conditions, such as cruising down the highway on a cool day, and then would probably run about the same temperature when the heat load is high, which would result in a wider swing in temperatures than if you had not bypassed the thermostat. This, by the way would not be a good thing.

[WizardBlack]

If I run the coolant hoses into the UPPER thermostat housing, will that work? I figure it is equivalent to running directly into the radiator inlet.

 

From the looks of RossMan's diagram, he's planning on running into the lower thermostat housing?

 

Thanks! -Hugh

 

I think the simple answer they're kicking your way is that doing that would add more complexity to the behaviour of the cooling system. Besides, there really isn't much of a place to tap the line into on the upper. The lower is a nice block of aluminum with (typically) one or more unused threaded ports.

Getting all the coolant flow back together before it hits the coolant temp sensors in the lower is probably a wise idea as well.

 

As an update, in 70 degree weather, my car idles pegged at 160 steady. I had yet to dial in the EDIS sensor after reassembly and realized it was about 6~7 degrees retarded which didn't help with engine bay heat before.

[X64v]

This modification isn't intended to help the car run any cooler, in traffic or otherwise. The same amount of heat is still being put in the water, same amount still being put into the air by the radiator. This is only to keep chambers 5 and 6 from developing hot spots under extended load conditions.

 

As a follow up on my engine, after almost a year now of running these bypass lines (9,000 miles on them), the main difference I've noticed is I no longer have a wide range of light ping before blowing a gasket. Before these lines, there was a lot of spark timing range where it would induce light ping but not blow the gasket. Now, it seems as if I go from no ping straight to a loud knock and blow the gasket. I would attribute this to bringing the 'ping threshold' on 5/6 closer to the rest of the cylinders, so either none are pinging, or most are.

[hughdogz]

Good thing I only got as far as buying the bung

 

I appreciate all the info Guys!!

[ktm]

This modification isn't intended to help the car run any cooler, in traffic or otherwise. The same amount of heat is still being put in the water, same amount still being put into the air by the radiator. This is only to keep chambers 5 and 6 from developing hot spots under extended load conditions.

 

Actually, both myself and Jeff Priddy noticed that the car does run a little cooler. The lines at #5 and #6 promote flow from these eddy/dead spots, flow that was not previously occuring. Additionally, we noticed that the car came up to temperature more quickly and stabilized sooner.

[jgkurz]

This modification isn't intended to help the car run any cooler, in traffic or otherwise. The same amount of heat is still being put in the water, same amount still being put into the air by the radiator. This is only to keep chambers 5 and 6 from developing hot spots under extended load conditions.

 

As a follow up on my engine, after almost a year now of running these bypass lines (9,000 miles on them), the main difference I've noticed is I no longer have a wide range of light ping before blowing a gasket. Before these lines, there was a lot of spark timing range where it would induce light ping but not blow the gasket. Now, it seems as if I go from no ping straight to a loud knock and blow the gasket. I would attribute this to bringing the 'ping threshold' on 5/6 closer to the rest of the cylinders, so either none are pinging, or most are.

 

Actually, both myself and Jeff Priddy noticed that the car does run a little cooler. The lines at #5 and #6 promote flow from these eddy/dead spots, flow that was not previously occuring. Additionally, we noticed that the car came up to temperature more quickly and stabilized sooner.

 

Sean and Bo,

This is really interesting feedback. My car has always pinged slightly if I turn up the boost above 10psi. I have tried COLD plugs, various AFR's, ran more and less timing. Nothing made a difference other than higher octane fuel. The car runs really well and makes the power it should but I have always struggled with random pinging. (Note: I have a very sensitive ear and NEVER power through a ping) Thanks to your posts, I'm starting to think my rear cylinders may be the source of the pre-ignition.

 

All,

Is there any advantage to bypassing cyl 4, 5 and 6 or just 5 and 6?

[ktm]

John,

 

I previously posted some pictures, as did Cygnus-x (IIRC), of my head gasket showing detonation damage at 4, 5 and 6. The worst was at 5 and 6 with 4 showing a bit of an egg shape. I used this observation as the basis for running the bypass at 5 and 6.

 

You could certainly run a by-pass at 4, 5 and 6 and as our resident historian Tony D would add, professional teams ran a by-pass line to a manifold for each cylinder. I focused on 5 and 6 because that is where I saw the worst of the detonation damage on my head gasket. Also, having only two ports allowed me to utilize my existing coolant routing without tying lines together similar to Sean's setup. If you look at my arrangement, 5 feeds my turbo's coolant section that then returns to the bypass line to the water pump inlet; 6 goes to the port on the drivers side of the lower t-stat housing. Before I tapped the head, I was running a line from the lower t-stat housing to my turbo and the return was to the by-pass to the water pump inlet.

[jgkurz]

Thanks Bo! Looks like I'm starting a new project...

[datman]

I had problems with pinking on my engine for some time...I have a knocksense kit fitted and it would flash under full load at 4000 ish rpm 12psi boost 18deg timing.....I couldn't hear it so I suspected I had sensitivity too high on the knocksense box....I dropped the boost and tried again and had no warning flashes.....I fitted a heatshield under my inlet manifold/fuel rail and took 2 deg timing off the the problem areas and it stopped.

I would imagine plenty of engines are knocking slightly....not enough to cause instant failure but not good in the long term.

Great Thread though, I think I will modify my spare head.

[WizardBlack]

Actually, both myself and Jeff Priddy noticed that the car does run a little cooler. The lines at #5 and #6 promote flow from these eddy/dead spots, flow that was not previously occuring. Additionally, we noticed that the car came up to temperature more quickly and stabilized sooner.

 

I did as well, actually. I didn't really think about the warmup thing, but it does that too.

Click my project car in my sig and you can see some pics of my own install.

[X64v]

Actually, both myself and Jeff Priddy noticed that the car does run a little cooler. The lines at #5 and #6 promote flow from these eddy/dead spots, flow that was not previously occuring. Additionally, we noticed that the car came up to temperature more quickly and stabilized sooner.

 

Hmm, I haven't noticed any change in warm-up time or operating temp at all. But then again, the car runs against the 160 degree T-Stat I have all the time except in heavy traffic when it's 100+ out. Perhaps it's because I have both 5 and 6 running back into the water pump, uncooled.

 

John - Now that I know that doing just 5/6 seems to work, I plan on eliminating the stock T-Stat housing and running them all into some sort of runner or something, as Tony D, et al. have talked about elsewhere. Also, FWIW, I've blown a head gasket at number 4 without blowing 5 or 6, so I'd guess doing all three rear cylinders would be worth it.