Cylinders #5 and #6 strike again - Head Gasket #3

[schwiplarkin]

how thick is it? interested in selling one?

[z-ya]

I would rather spend $80 and replace a head gasket than sink ringlands. I just need to tune for California gas.

 

Brian, I am not going to run a manifold, but I am going to tap #5 and #6 and to get the hot coolant out faster.

 

How do you have the coolant lines routed two and from the head and heater core (do you have a heater core hook up)?

[ktm]

z-ya, I do not have a heater core. I have the return line where the coolant leaves the head to go to the core, and that returns to the water pump inlet like the stock configuration. The lines to the head enter at the pump and return via the thermostat housing.

[1 fast z]

I milled it on a mill.

[z-ya]

z-ya, I do not have a heater core. I have the return line where the coolant leaves the head to go to the core, and that returns to the water pump inlet like the stock configuration. The lines to the head enter at the pump and return via the thermostat housing.

 

So let me just confirm, you have a 5/8" hose running from the rear of the head on the passenger side to the water pump inlet, also on the passenger side.

 

The only hose connected to the thermostat housing should be the big one going to the top of the radiator. So three coolant lines:

 

- Bottom of radiator to water pump inlet

- water pump inlet to rear of head

- thermostat housing to top of radiator

[ktm]

So let me just confirm, you have a 5/8" hose running from the rear of the head on the passenger side to the water pump inlet, also on the passenger side.

 

The only hose connected to the thermostat housing should be the big one going to the top of the radiator. So three coolant lines:

 

- Bottom of radiator to water pump inlet

- water pump inlet to rear of head

- thermostat housing to top of radiator

 

Exactly.

[wigenOut-S30]

Bo, 12.1-12.5 seems awful lean at anything above 8-10psi of boost. expesially when running 91 oct. I know with Meth, Garrett tunes his car to 11.2-11.4 air fuel . I think you are simply just running lean. I would get her back togeather and tune for a much richer format. I tune my Z for 11.5-11.7 WOT.

[Tony D]

Exactly.

 

I would NOT run that head line to the inlet---that IS raising your overall temperature of the engine by taking water from the hottest part of the engine and shunting it DIRECTLY to the inlet of the engine---where it mixes with the radiator return line and warms it considerably! This is a PRIME reason many 240's overheat. That mixing should be limited to the internal 8 or 10 mm passage, and the external 8mm bypass line from the lower thermostat housing.

 

Think about this: The heater is a radiator and when the heater is 'on' and flowing water through it, it is cooling it therefore allowing NO increase in radiator water return temperature to the pump. When the heater is off, the bypass is OFF. NO FLOW!

 

On the 280ZX's they incorporated a poppett-style valve to open at EXTREME high rpms when the thermostat is closed, as the two 8mm bypasses are not sufficient flow to prevent cavitation of the pump when revved cold.

 

I would remove and plug that line IMMEDIATELY.

 

Then, I would consider either taking the 15mm line off the plug side of the head and shunting it directly to the thermostat housing...but usually the flow increase holes are added directly over the combustion chambers to allow any steam produced to vent 'up and out' as well as increase flow in that area directly out to the radiator.

[z-ya]

Think about this: The heater is a radiator and when the heater is 'on' and flowing water through it, it is cooling it therefore allowing NO increase in radiator water return temperature to the pump. When the heater is off, the bypass is OFF. NO FLOW!

 

He doesn't have a heater core in there, so there is nothing to block the flow. I always connect the heater core in parallel with the line that goes from the inlet to the rear of the head.

 

So you would eliminate the pump inlet to rear of head connection, and just run a connection from the rear of the head to the bottom of the thermostat housing?

 

Pete

[ktm]

So you would eliminate the pump inlet to rear of head connection, and just run a connection from the rear of the head to the bottom of the thermostat housing?

 

Pete, I believe Tony is suggesting to block the head connection all together and tap the head above #5 and #6 and run those lines to either the lower t-stat housing or the radiator.

[m4xwellmurd3r]

i wonder if this is why my Z overheats o-O

the heater core has been bypassed, but instead of plugging the line, the output from the back of the block hooks back into the water inlet. If this DOES cause overheating, well, i'm going to plug that thing ASAP.

man, i wish I had thought of that before, but that does cause overheating. the hot water from the back is now being recirculated into the system without being cooled, causing it to continually increase in temp.

[z-ya]

I have my N47/N42 mild road race engine setup like this:

 

- Bottom of radiator to water pump inlet

- water pump inlet to rear of head

- thermostat housing to top of radiator

 

It never exceeds the thermostat temperature (192F) during track sessions. The only time is get hot is after a session. If I shut it off, and then check the temp in a few minutes, it will spike to 220F, and then cools down. If I start it and let it idle, it cools back down to 192F. It has single electric fan.

 

I might try and change the rear of head connection to the t-stat housing.

[Tony D]

I have my N47/N42 mild road race engine setup like this:

 

- Bottom of radiator to water pump inlet

- water pump inlet to rear of head

- thermostat housing to top of radiator

 

It never exceeds the thermostat temperature (192F) during track sessions. The only time is get hot is after a session. If I shut it off, and then check the temp in a few minutes, it will spike to 220F, and then cools down. If I start it and let it idle, it cools back down to 192F. It has single electric fan.

 

I might try and change the rear of head connection to the t-stat housing.

 

I have seen 'plenty' of people with a loopped heater core. And in EVERY case when I block it off properly, overheating problems go away.

 

You can get away with a LOT on the cooling system, especially in the cooler, more temperate regions of the USA and Canada. But you try that stuff in the Desert Southwest, and you will be milling overheated heads on a regular basis!

 

That someone 'has done it that way' does not mean it's correct. Think about it logically, and you realize the system is designed for ONLY 'cooled' water to go in the water pump inlet, save for ONE small 8 to 10mm internal boring on the block.

 

Other than the later ZX 'poppet' valve which was added for extreme circumstances, nothing is flowing through that 15mm line on the side of the block, and nothing comes through the external bypass line that has not been somewhat, if not totally cooled. The bypass line usually heats the TB, and AAR valve, and the 15mm line goes through the heater core to be cooled before re-entering the coolant pump.

 

You use that line, you have a direct shunt---you may not see a temperature increase on the outlet...but what you have a DRAMATICALLY reduced internal block pressure due to the greatly increased flow. Add a slight heat increase in inlet temperature to a decreased pressure system and you have a recipe for nucleate boiling, and cavitation in the pump or the block perpindicular to the wrist pin...

 

That line being blocked off completely is NOT detrimental to the engine whatsoever.

 

Letting it recirculate uncooled---it's bad. just how bad will be determined by the condition of the rest of your system and operating environment. Lots of aerosol blocking UV and a 90 degree day in NH is better operating conditions than a 65 degree clear and sunny day in SoCal---road temperatures at the radiator will be likely 10-15 degrees higher (in the area of 104F) in SoCal, while NH will be maybe 95F.

[TrumpetRhapsody]

So the verdict is to plug the outlet at the back of the block if not using the heater core then?

 

Good to know, I have it going back into the inlet too

[m4xwellmurd3r]

Yeah, it makes sense to plug it. I smacked myself in the face when i realized how stupid I was when I was trying to diagnose my cooling issues. I do wonder though, if re-routing that back plug to go back into the radiator directly, if that would somehow help with cooling the engine. or maybe re-route it to go to the lower T-stat housing.

[ktm]

Nope. You missed the entire point of the discussion if you do that and have not solved the issue of stagnant water around #5 and #6.

[z-ya]

 

That line being blocked off completely is NOT detrimental to the engine whatsoever.

 

 

I understand that this would be non-detrimental to to engine, that is as long as it runs at a safe temperature.

 

Earlier in this post you mention that the block of flow from the rear of the head when the heater core mixing valve is closed caused all of the overheating problems in early 240Zs.

 

So do you recommend blocking it, or routing it back to the t-stat housing?

 

Sorry for the high jack....

[Tony D]

"Earlier in this post you mention that the block of flow from the rear of the head when the heater core mixing valve is closed caused all of the overheating problems in early 240Zs. "

 

I never said that, I said looping the hose from the head to the inlet causing a shunt will cause overheating.

 

The stagnation of flow above the combustion chamber on 5 & 6 is there regardless of heater operation.

 

If the heater is on, chances are really good you aren't in what would be termed 'extreme overheating environmental conditions'.

 

Somehow people think they need that flow out of the back of the head when they remove the heater from use. This is not the case. In normal operation, that petcock at the rear of the head is closed. People have to realize that---for some reason they don't. Plugging it does nothing more detrimental than driving around with your heater 'off'.

 

But looping it, that causes the shunt. The only conditions where that shunt should exist are the conditions previously mentioned about cold-drive off and ultra-high rpm operation before warmup. This is why the supplemental bypass poppett valve was added to the ZX.

 

If someone MUST loop that hose, I'd not do it unless that ZX Poppett valve is in the line. Then it will stay closed during warmup, and ONLY open the shunt during higher revs when the thermostat on the outlet of the block is closed and can't provide sufficient flow to prevent cavitation of the pump from operating below it's minimum flow curve.

 

The safest thing to do is plug the head, and simply let your engine properly warm up before running to 6KRPM...

 

***************

As to routing it to the T-Stat Housing...I don't think that will help the situation. I think that will exacerbate the stagnation of flow above the #5&6 head combustion chambers, this petcock will be taking block waterflow and shunting it around that upper area in the head.

 

This is why tapping the head above the combustion chambers and routing it to the T-Stat housing helps the situation, it allows the block flow to go to the top of the head and exit directly.

[z-ya]

Thanks for the clarification Tony. I'm not seeing an overheating problem, but I do have that temperature spike problem after a session when I shut it down. I will try plugging the port in the rear of the head, just to see what happens.

 

Pete

[ktm]

Pete, I always let me car idle for a bit after running it hard before shutting down to help mitigate the temperature spike. I do this to allow the coolant to continue to circulate. Another option would be to go with an electric pump and have it continue to run after the car shuts down.