by Mike Kojima
The issue of Nissan 370Z’s running excessively high oil temperatures has been speculated upon since before the cars launch when photos of pre production vehicles fitted with racing style oil coolers started to appear on the internet. These oil coolers with bar and plate heat exchangers, race car AN fittings and braided steel lines were clearly not parts made with production intent. Why did the cars have these coolers, was the question echoed across the web.
We figured that the coolers were just a precaution, installed on press fleet vehicles as cheap insurance against journalistic abuse or for durability in special arrive and drive promotional event use which can be more brutal than racing.
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| Just a heat machine… The VQ37VHR engine found on the 370Z and the Infiniti G37 runs high oil temperatures. Lots of oil churning caused by its variable cam timing system is the main suspect |
Since we have actually started to work on and modify the 370Z we have come to realize that high oil temperatures have the potential to become a problem on these cars. We have recorded oil temperatures of 260 degrees plus on 370Z’s on the dyno, in brisk driving and simply in heavy traffic. Several times we had to stop dyno testing or slow down while driving to allow oil temperatures to drop. This is not race track flogging, a dyno run is a very short burst at wide open throttle through one gear, brisk driving is not an illegal balls out cannonball run, its driving a sports car how it was supposed to be driven and heavy traffic is something any car should be able to deal with easily.
260 degrees is the beginning of the danger zone or about as hot as can be tolerated by an engine without risk. At 260 degrees, oil breaks down rapidly losing its ability to lubricate and forming sludge. At this temperature the engines bearings which are made of soft malleable metal start to soften and lose there load bearing capacity. This is the point where damage can start if the car is driven to the limit.
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| Here is an oil cooler that we spotted on a pre-production 370Z many months ago. You can see the bar and plate type heat exchanger peaking out from behind the grill opening |
Why does the VQ37VHR run so hot? We have several theories. One is that the VVEL/ CVTC variable cam timing system needs a lot of oil pressure to function correctly. Oil pressure must be able to both move the rotor position inside the intake cam gear to advance and retard the cam as well as operate the eccentric that controls the valve lift and duration. These devices must be moved quickly against the great frictional and spring tension forces generated by the valvetrain. A lot of oil pressure and volume are needed to get these devices to work. This means a big oil pump which the VQ37VHR has. A lot of oil is getting pumped up to the heads, probably faster than it can drain back into the pan. At high rpm, this means that there is much less oil in the pan and the oil remaining gets pumped through the engine many more times, gaining heat as its circulated.
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| After passing through the heat exchanger, the air exited into the wheelwell on the pre production 370Z oil cooler |
The oil pumped to the head drains back, to the sump, some of it landing on the crankshaft where it becomes part of the churning windage cloud gaining more heat as it’s whipped around by the engines reciprocating parts. The big oil pump also bypasses a lot of oil at steady throttle and low speeds where the continually adjustable CVTC/VVEL valvetrain is more or less static. The oil in the pan is pumped through the pump where it get heated by the pump’s action and bypassed to the pan, where it is again rapidly circulated by the oil pump again and again picking up more and more heat. Thus the VQ37VHR becomes an oil temperature generating machine.
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| The pre-production factory 370Z oil cooler used a sandwich adapter from the oil cooler to pick up the oil |
What can be done about this? Well if you are not an abusive driver, one who bought the 370Z as an image statement and you drive normally and do not compete in any sort of motorsports, you are probably ok. It would be advisable to only run the highest quality synthetic oil and maintain a frequent oil change schedule. If you drive hard, participate in track days, autocrosses or frequent the drag strip, we feel that more needs to be done, principally adding an engine oil cooler.
