Diagnosing Engine Problems Chapter 3 part 1 Diagnosing Engine Problems

It is important to diagnose the cause of a problem before performing a repair Possible reasons for oil consumption Causes of rough running or lose of power Engine noises Oil pressure problems Cooling system problems

Diagnosing before a repair This starter drive frame was the result of a catastrophic engine failure How ever the same damage can result from a failed belt driven accessory Such as a frozen a/c compressor or power steering pump

What is acceptable oil consumption GM has a tsb that states that 1 quart per 2000 miles is considered normal Aggressive driving habits such as 3000 rpm to redline With frequent deceleration (engine braking) can result in 1 quart every 500 miles Towing a trailer can also have this affect especially on the freeway

Rapid loss is a complaint you might hear from A customer when they are on a trip like a vacation If they do most of there driving in town at low speeds This can result in extra fuel and water build up in the oil pan. Then when they have a long road trip and the oil fully warms up The fuel and water evaporate and then when they check there oil level it can be very low

Bad valve guides or defective valve guide seals These can sometimes be seen as smoke from the tailpipe On a deceleration High vacuum conditions such as this cane pull oil into The combustion chamber

Bad valve guides seals can also cause carbon buildup on the neck of the intake valves Also if a spark plug is oil fouled on one side only this can be the same indication

Oil consumption due to worn rings Due to higher crank case pressures do to blow by (chapt. 1) And higher engine vacuum on the intake stroke Oil migrates up the cylinder walls and into the Combustion chamber

Plugged oil rings can cause the same affect as worn rings. This is generally due to poor maintenance habits Ie: Not having oil changes within proper intervals

Holes or slots behind the oil control rings allow the rings to scrape off excessive oil and return it to the crankcase When inspecting piston that you are reusing. Be sure these areas are clear

Increased oil use after a valve job This can happen on higher mileage engines Due to the increased pressure in the combustion chamber after a valve job, the engine can end up with more blow by, past the worn rings. Anytime that a valve job is performed on a high mileage engine, the consumer should be advised of this first.

Excessive rod bearing clearance High mileage engines with worn crank bearings Can have the affect of throwing to much oil on the Cyl. Walls for the rings to control. Usually at higher engine speeds This can also cause low oil pressure as the oil Leaks out of the bearing to crank clearance that Is beyond spec. for the engine

If the oil consumption is after an engine replacement Be sure that the right oil dip stick was installed Same engine in different vehicle may have had A different oil pan requiring a different dip stick Thus causing a over fill condition which splashes To much oil on cyl. walls

Plugged oil drain back holes Cylinder heads have oil drain Holes in them so that rocker arm Oil can drain back to the oil pan If these holes plug up then the only Way for the oil to return to the pan Is to flood the valve seals and inter The combustion chamber. Any oil in combustion chamber Get burnt

PCV system problems A pcv system that is not sealed can cause a rise in crankcase Pressures, causing oil consumption. The average flow of a pcv system is about 5-8 cfm if above 8 cfm this indicates the ring are not sealing correctly If there is a vacuum leak, then the pcv will pull unfiltered air Into the motor, which will cause engine wear. One way to check pcv operation is to pull the breather hose Off at the filter and plug it with your finger. After a few seconds You should feel a slight vacuum on it.

Oil leaks Oil leaks are a large account for complaints of oil consumption Not only can they be aggravating for the customer but they can Cause several hazards to the engine and vehicle. A loss of 1 drop of oil every 30 feet results in about 3 quarts Of oil every 1000 miles.

Ways to locate oil leaks You can clean the engine the let run until you can see the leak Either on the motor or on the ground. Or you can put dye in the oil, run and drive vehicle for a few miles The n use a black light to locate where the dye is leaking out.

Homework due next class Miscellaneous leak detection methods Read chapter 3 to page 64 Last topic will be Miscellaneous leak detection methods