Quote:
Originally posted by Sean K.:
As for overheating with a skid pan.....How do you guys that are saying that come to that conclusion? What exactly are you overheating? It certainly isn't going to be the engine. Yes, you may heat up the floor boards and any wiring in the covered area more (especially if the catalytic converter is housed between the floor and skid), but it's highly unlikely that there's anything that will be damaged by the relatively minor increase in temperature....and that includes the transmission and tcase. Again, easy test if we can find a few volunteers....one equipped with no skid and one with a skid in the same local area. That is, if you guys really wanna know for sure instead of merely speculating about something with which you have no experience.
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Overheated trans fluid is one of the biggest killers of an auto trans. In addition, the pan itself is used as a cooling medium (finned pans increase cooling efficiency). The damage to the trans, due to overheated fluid, will not be done in a few thousand miles, it will be done in 20-30K miles. The fluid will degrade over a period of time, causing internal trans failures.
Trans fluid has a frictional coefficient designed into it, that is why there are so many different trans fluids on the market. Heat, is one of the major factors in deterioration of trans fluid. Heat, over a period of time causes the frictional coefficient of the trans fluid to change, in the case of the 4L transmissions used on GM vehicles, it cause the fluid to become more slippery. The lower frictional coefficient will cause clutches to slip, and this initial slippage will not be that noticeable, since it is happening slowly over a period of time.
Heat also causes the viscosity to change as it does with engine oil. The designed life of trans fluid is calculated on the maximum temps the trans will be normally run, that is one reason why many vehicles required a fluid change on vehicles that are not run at high speed (taxi cabs, police cars, delivery vehicles, etc.). Running a vehicle at low speeds does not create enough airflow past the pan and the trans itself. (Same with an external trans fluid cooler.)
Therefore, the easy test of a few days travel will prove nothing, other than the trans fluid is or is not running hotter than normal. Pretty sure I can save your trouble, since enclosing the trans in a shield will cause it to run hotter, due to the trans heat itself not escaping, and adding the heat buildup from the cat.
I would recommend to anyone adding a full underbody shield to at least change their trans fluid every 10-15K. In fact, I would recommend a full trans fluid flush. A normal trans fluid change only replaces the fluid in the pan, the remainder of the old trans fluid is still in the passages, clutches and servos of the trans. In fact, on the 4L70 trans used on the H3, the pan will contain 5 quarts of fluid, the remainder of the trans hold an additional 6 quarts of fluid. Therefore, a fluid and fill is the only way to replace all the damaged fluid.
At this time, the trans engineers at GM I know would never recommend a full body undershield, unless it is bolted on for minimum use during severe off-road driving. That is probably the reason GM Accessory parts sells only the ladder type, since it is assumed most will leave the underbody protection on all the time.