In this thread I will explain in full detail as to why I prematurely warped the heads on my engine. I hope that this thread can provide a basis for other in the event they are experiencing some of these symptoms.

After that ordeal I decided to investigate WHY it occurred when I never overheated past 70% on the dial.


So that everyone can understand the vehicle of topic:
2003 G35 Sedan
Automatic Transmission with PWR 4 Core Radiator and 2 Separate Transmission Oil Coolers.
Intake, M/D 1/2inch spacer, Headers, UR Pulleys, Full Exhaust.
20inch Wheels.
OEM Thermostat
(Fan CLUTCH AT THE TIME)

Ever since the inception of the vehicle (purchased it used 35k miles) I noticed the car ran slightly “hot”. Immediately I addressed the issue with the dealership and they agreed to take a look into it and eventually changed the fan clutch at their cost. The temperature did drop and stay stable for about 2-3 Months.

Then again the problems began arising. Due to the fact that it was recently replaced it made me wonder, perhaps it was the OEM fan clutch being defective so I purchased an aftermarket fan clutch from Advanced Auto Parts. It worked well too!

Till about 120,000miles it ran fine. Since it ran so damn well it slipped my mind to change it and the fan clutch throughout time gave up.

Regardless, I always caught the issue before it became detrimental.

After the rebuild and the e-fan conversion I learned with the OBD-2 scanner/live data monitor. That the OEM radiator although thin works incredibly well. It worked well because since it’s so thin the amount of fluid inside the fins are cooled rapidly with minimal effort. Where as the PWR would take 3 times as much to do the same. Why?

Simple, Volume! The amount of volume inside the radiator is greater than the volume of cooling air needing to reduce the temperature.

For example:

Recently I installed an efan conversion on another G35 sedan. Only difference was the radiator one being OEM and my radiator PWR’s.

The oem radiator conducts the heat quickly. The pwr takes a long time to heat up. But once heated it takes 3 times as long to bring the temperatures down. This is not a bad thing. In all fairness it’s a great thing.

Now where I learned from tuning the efan controllers:

When driving at below 30mph the car makes more heat than the radiator can cool down, regardless of radiator pwr or oem. This is why our cars come with fan clutches and electronic fans. And of course when you are driving the temps drop.

But, what happens when you drive REALLY rough, and come to a complete stop and then turn off your car ???

What happens is simple, heat soak! The radiator may be colder than the engine but the temperature from the engine will affect the radiator itself.

The combustion chamber pops at about 2000-3000 degree’s. Water does a great job of cooling this down. But you can only cool so long as your car is on.

This is where I came to realize. That if you drive hard, and do not give the car at least 5 minutes to circulate some cooler water, you are doing what I did to my engine. Damaging it!

Moral of the story:
Let the car cool down just as important as warming up in the mornings.

 

Good stuff, thanks Eric.

 

Great advice, but what proof do you have that running hard then shutting the engine off right after caused your heads to warp?

 

Simple.


Since there is no water movement once the engine is turned off the pressure will climb due to the heat. If the pressure is greater than the cap can flow SOMETHING HAS TO GIVE.

I've seen temperatures climb up to 226 degree's with a OEM radiator and a fan clutch when pushed really hard. So that means that if you happen to turn off the car after a hard run/or two the engine will be hotter than the radiator but since the radiator is only a small fraction of what the engine has liquid. It will soat the heat from the engine. Since there is no cooling rapid water inflation will occur, metals expand. Now, once you turn the car back on (say 15 minutes) the fan clutch will be 100% activated which will move lots of air in a short amount of time and bring the temps down from 220+ to 188 (where the fan clutch likes to run)

that constant cycle hot/cold cold/hot will eventually cause premature head warpage, also radiator end tanks will leak, etc...


There is a reason why OEM G35 efan cars engage their fans at 203 degree's and then cut off at 195. thats to keep the temps down to a constant as possible level. Once you are driving the temps do drop to about 181 but coming off the highway you'll notice the temps spike up radically.

But in street use, with stop and go traffic the temps move up in a linear manner.

Which goes to show that with more RPM the hotter the engine gets even if you're doing 55 (which provides over 100x more air than your fans can move).

 

Thanks for the info..

 

thats great information
close attention should be paid to other things as well. it is a true statement that temps are high when shutting down, but car makers are aware of this. they develop the cooling system to avoid too much heat. Once something in their design is changed(modding) all their developement goes out the door. adding a larger radiator and not replacing the thermostat and fans accordingly may cause some damage. there are also other things that give heat trasnfer other than your coolant. many people dont know that your engine oil is part of engine cooling. not only does it lubricate, it also acts as a cooling agent. so it is very crucial to have the correct viscosity of oil, correct water to coolant, correct temp thermostat, and E-fan thermostat for your type of motorsports.
the same amout of coolant stays constant within the engine water jacket. only the volume within the radiator can you hold more. the E-fan thermostat should have been installed with the larger radiator and should stay on untill the temps go low enough to turn it off(with the car off). if a high enough temp was reached during driving, your coolant temp sensor(s) will pick this up and pull timing accordingly to prevent damage...hard driving would actually be taken down a notch automatically. also when high temps are reach your A/C fans should have activated. with the engine stopped, yes there are high temps..but the heat source was cut off, so no extra heat will be made. overheat after shut down is rare, but it occurs.
reasons for overheating>
incorrect coolant to water ratio
faulty water pump
air pockets
low water/coolant levels
faulty radiator cap
faulty thermostat & E-Fan thermostat
insufficent air flow
plugged radiator
leaks in the system
belts
low oil
retard timing
faulty engine & coolant temp sensors
blocked heater
incorrect CFM fan installed on aftermarket radiator
incorrect tunning of E-fan thermostat
ect...

just adding alittle more info to what you have already provided.

 

Usually around 225*F is when you should start to get worried about aluminum heads and warpage. I actually know of a few manufacturers that put indicators on them to show if the head was subjected to temps greater than 225.

200* is usually the magic number for modern fuel injected cars for normal operation. Higher and you start getting into the danger zone...cooler and the engine is not running at proper efficiency.

 

I agree. So much has been changed on his car, it's really hard to say if the problem is a Nissan one or something created by all his modification to the cooling system as well as increasing power which adds heat. I'll just add that I've been working with VQ motors since about 1998 and I've never heard of one instance where the heads warped whether it was because of heat or something entirely different. If there is a problem with the VQ motor, it really lies in the VQ35s which have weak rods (increased stroke) and soft rings (to improve MPGs). The old VQ30s were stout as hell and adding boost is a non-issue. The only thing holding those motors back are the injectors which max out at around 330-350whp.

 

so what youre saying wouldnt a lower temp thermostat solve the problem?

 

Not always.

 

It is a potential that my car did have a problem from factory, and/or something I enhanced made that problem.

 

Yup it's a hit or miss sometimes. Too many variables. I've been boosted for awhile now. My cooling system is entirely stock with a I/C blocking the radiator and PS cooler. No nismo bumper either.. Stock bumper. Ive never had a problem. I've always warmed up and cool down(turbo timer) properly to avoid any over/under heating.