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Sometime in the last few years, in an effort to be greener, Nissan discontinued the use of lead in all engine bearings. We know of this through discussions of sources deep within Nissan which will have to remain unnamed. At this time the engineers at Nissan noticed that warranty claims for bearing failure in the RB26 GT-R engine, another Nissan engine noted for running high oil temps, spiked. Nissan launched an intensive study on the reasons of this bearing failure and discovered that the new environmentally friendly bearings started to loose their load bearing capacity at temperatures as low as 260 degrees. Although there was plenty of reserve strength for normal passenger cars, the turbo high output RB motor pushed many sets of bearings to the failure point. Although you think of lead as a very soft metal with a low melting point, it was still a major contributor to the bearings mechanical properties and resistance to heat.
So as the oil temperatures climb, the bearings soften and loose their load bearing capacity, if the temperature climbs past 300 degrees and the engine is being pushed hard the bearing material can start to flake and spall. This disrupts the hydrodynamic film allowing metal to metal contact, resulting in catastrophic failure of the bearings, the crank, rods and even the entire engine often within seconds. Oil also begins to deteriorate quickly at temperatures above 260 degrees. It starts to oxidize and thicken, loosing its lubricity while forming sludge and varnish. This further compounds the problem, generating more drag and heat in the bearing/crank interface area.
Why does the VQ37VHR have such high oil temperatures? We have several ideas. The VVEL/ CVTC variable cam timing system needs a lot of oil pressure and volume delivered to it to function correctly. Oil pressure must be able to move the rotor position inside the intake cam gear to advance and retard the cam. The VVEL system with its many pivots, links and sliding surfaces needs a lot of lube to be pumped to it to keep it lubricated. These devices must be moved quickly against the great frictional and spring tension forces generated by the rotating valvetrain.
Thus the VQ37VHR has a big high capacity oil pump. A big high pressure pump puts heat in the oil from the pumping action itself. A lot of oil is pumped up to the heads to operate the VVEL system and released to the area under the valve cover, 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 in the pan gets pumped through the engine many more times, gaining heat from the pump, valvetrain and bearings as its circulated.
As the oil pumped to the head drains back to the sump, much of it lands on the rapidly spinning crankshaft where it becomes part of the churning windage cloud of oil and air gaining more heat as it’s whipped into a fog of oil and air by the engines crank and rods. 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 370Z long lead press car has it's oil cooler pickup in the same place as the aftermarket parts, by the oil filter |
Now what can be done about this? Well the obvious thing is to add an oil cooler and many feel that Nissan should have done this from the factory. If you consider Nissans rational, it was probably to save weight and cost. Nissan had set aggressive weight and cost targets for the 370Z during development. The goal was to provide a good power to weight ratio and to provide an excellent performance to cost ratio for the customer as well. Every single piece of the car was scrutinized to meet these goals. It was probably judged somewhere that it was cheaper to protect the engine with basically free ECU fail safes than to add an oil cooler that would add weight and cost to the car. The probable rational was that most likely only a small portion of the customer base would actually put the car through the paces on a frequent basis enough to where serious oil temperature issues would come into play.
Well it seems like this decision may not have been the best as reports of oil temperature issues are starting to come in even under typical driving conditions such as heavy traffic or hot weather driving. Is this a cause to panic? Not really. The reason is that if the oil temperatures climbs under normal conditions, although this is far from favorable, the engine is not being pushed anywhere close to the limit and has plenty of reserve load capacity. If the engine is pushed to where damage can start to occur, The ECU goes into limp mode which although annoying, puts a halt on the situation and protects the engine. Is the 370Z the only car to do this? No way. The BMW 330 is infamous for doing this as was the last C6 Corvette we drove.
What can be done? Well if you participate in motorsports events such as autocross, drag racing, track days and wheel to wheel racing, an oil cooler is probably mandatory. If you drive in a sporting manor in the street or drive in heavy traffic a lot and run into limp mode or observe oil temps in the 260 degree range, an oil cooler can’t hurt. In any case we recommend high quality synthetic oil changed frequently at no more than 3000 mile intervals. For sports use, Technosquare, Stillen, Nissan Motorsports and ARC currently make high quality oil cooler kits. We like the Technosquare kit as it uses fewer 90 degree fittings for less pressure drop and lighter and less abrasive Earls Ultralite hose with the smooth aramid cover, but essentially all 4 of these coolers have equivalent excellent quality and performance.
Read about Technosquare oil cooler, evaluation here:
