Mike Kojima posted on May 18, 2009 08:31
If you are reading this, you might have read about these things on a forum, you might have heard the rumors or you might have experienced some of these things yourself on your car. There is a lot of misinformation floating around on the net and hopefully this will help answer some of the questions about these incidents.
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| The Technosquare oil cooler kit is a good part for the 370Z, Stillen, Nissan Motorsports and ARC also make quality kits for the 370Z |
One of the main issues is that the Nissan 370Z and Infiniti G37 with the VQ37VHR engine experiences high oil temperatures. The high engine oil temps can cause the engines ECU to put it into a limp home mode where the engine rpm is limited, first to around 6000 rpm and if you don’t start to behave, a lower limit of about 3500 rpm is engaged until the oil temperatures drop below around 280 degrees and the key is cycled. The VQ37VHR is very prone to suffer from high engine oil temps during any sort of extended high speed driving such as motorsports events, and even non competition events such as track days and Autocrosses. The engine can also suffer from high oil temps even with short burst of full throttle use such as on an engine dyno, drag racing and even bumper to bumper traffic.
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| This 370Z long lead press car has a hidden oil cooler in the drivers side front wheel well, probably to help keep the engine from going into limp mode during abusive driving |
To understand limp mode we must understand what it’s protecting in the engine. The most oil temperature susceptible parts are the engines crank and rod bearings. The engines bearings are made of soft metals, such as aluminum, tin and zinc with other trace alloying agents such as indium which refines the metals grain for better mechanical properties. The reason why soft metals are used is that they offer good embedability. If hard contaminates are present in the engines oil such as casting sand, metallic particles, hard carbon bits and dirt, a soft bearing surface will allow the particles to become embedded into the surface of the bearing where the damage to the bearing and crankshaft can be limited. The contaminating particle will be soaked up by the soft bearing instead of being ground into the hard steel journal surface of the crank with damaging effect.
Soft metals can be used as engine bearings because under normal conditions, the crankshafts journals never touch the bearings surface. Since the liquid oil layer is not compressible, the crank rides on a pressurized hydrodynamic film of oil a few thousands of an inch thick that is maintained on the bearings surface by the engines oil pump. The oil pump must maintain pressure (this varies for as low as 5 psi at hot idle to more than 60 psi at higher rpm) and continually replenish the oil because the oil leaks out at the edges of the bearing and is flung out by the centrifugal pumping action of the rotating rod journals. This circulation is necessary because the shearing action of the oil in the boundary layer between the rotating crank journal and the static bearing surface creates heat and this heat must be dissipated. Most of the heat is removed by the oil as it passes though the interface between the bearing and crank.
The bearings, although soft still have to bear a heavy load because the incompressible liquid oil film transfers the forces acting upon the engines reciprocating parts to the bearings, thus the bearings have to withstand thousands of pounds of force even though direct contact does not happen. The best engine bearing have high embedability with a high load bearing capacity.
Usually everything works fine until a couple of things happen. In the case of modern late model engines, the green movement is to blame for part of the problem. In the last few years, Nissan has worked hard to make their cars green and more recyclable. In an engine traditionally one of the most toxic areas was the bearings. A few years ago, many Nissan bearings were made of trimetal construction using layers of lead, zinc and tin alloys of different percentages. This tri metal construction has been a mainstay of heavy duty bearing construction and composition for decades. The old Nissan bearings were very strong, heat resistant and durable. It’s a little known secret that old L-Series Nissan bearings are so strong and durable that many race engine builders use them, adapting them to other engines. The Infiniti IRL engine used in Indy cars used off the shelf L-Series bearings for this reason.
Discuss on our forum here:
Oil temp overheating and limp mode
http://www.370z.com/Forums/tabid/88/aff/7/aft/246/afv/topic/Default.aspx
The $300 oil change
http://www.370z.com/Forums/tabid/88/aff/7/aft/279/afv/topic/Default.aspx
Oil temp Issues
http://www.370z.com/Forums/tabid/88/aff/7/aft/205/afv/topic/Default.aspx
oil cooler and diff cooler questions
http://www.370z.com/Forums/tabid/88/aff/7/aft/332/afv/topic/Default.aspx
Technosquare oil cooler
http://www.370z.com/Forums/tabid/88/aff/7/aft/233/afv/topic/Default.aspx