Around The Block
Separation of Engine Coolant, Exhaust, Oil and Vacuum
By Don Fedak
Have you heard about the dinosaur that went to a shrink because of "terrible recurring dreams that involve numbers and letters … 10W30?"
Every engine builder's nightmare also involves oil because no remanufactured engine will run very long without an adequate supply of clean oil. Previous columns have discussed the common problems of bottom end oil leaks due to worn shafts (Automotive Rebuilder, 3-99) and oil consumption from the middle of engines due to piston ring design, installation and wear (Engine Builder, 9-03).
But many of us have also seen engine oil mysteriously disappear or become contaminated in the absence of any visible leaks from gaskets and seals or smoke in the exhaust. The purpose of this column is to explain how excessive engine oil consumption and damaging oil contamination, mainly due to coolant leaks from other than head gaskets, can also originate in the top end of engines, i.e. the cylinder head(s) and intake manifold.
We once sold a factory remanufactured 4.1L V8 Cadillac. The owner returned to report that he had checked the level and had to add oil to the crankcase at least six times in one month and asked, "When will it stop burning oil?" There was no visible exhaust smoke because the catalytic converter burned all of the oil that left the combustion chambers. But many of the spark plugs had thick carbon deposits on one side. The engine was replaced under warranty because the positive valve stem seals did not fit tightly on the valve guides.
A 2.8L V6 Ranger engine started to use oil two weeks after it was installed because the cheap gaskets supplied by the production engine rebuilder became oil soaked and slowly disintegrated, allowing oil to enter the intake. No engine damage occurred because, as in the previous example, the owner checked the oil "religiously" to protect her investment in a replacement engine.
We were asked to supply a 350 V8 engine to the new owner of a used GMC motor home that was a "steal" because the original engine had spun a rod bearing. Over a year later, our rebuilt engine developed a knock and spun another rod bearing. When the installer returned our engine the intake manifold was still installed. We eventually traced both of these bearing failures to contamination of the engine oil by exhaust gases entering the crankcase via a crack in the crossover passage in the original cast iron intake manifold.
Some years ago, after we rebuilt his 390 V8 Ford, a customer asked us to install his new aluminum intake. Fortunately, after he installed the engine in his Mustang he noticed that coolant was running into the oil pan almost as fast as he could pour it in the radiator. His new "name brand" intake was badly warped right out of the box! As a result of this experience, we always check intakes, new or used, to determine if they are warped and require resurfacing.
Ever since, as a matter of policy, we will only clean and check intake manifolds and then set them on an engine. We no longer do any "favors" and install intakes.
After installation, a 318 V8 Chrysler we recently rebuilt wouldn't idle properly or pass an emissions test. After his third attempt, the installer finally got the intake manifold gasket to seal. Last we heard, he is still trying to convince the owner that the oil leak at the front of the engine is coming past the worn harmonic balancer.
For an example of how hot exhaust gases can produce coolant contamination of engine oil, look no further than the plastic upper plenum of late model GM 3.8 V6 engines. The coolant passage adjacent to the point in the upper plenum where hot exhaust gas is injected for EGR also happens to be the highest point in the cooling system. What happens, especially when an air pocket forms in the coolant? The plastic separating the hot exhaust from the cooling system is breached and the car comes to a stop just ahead of a big cloud of steam reminiscent of "Old Faithful." We get to rebuild the engine and when the owner picks up his car from the installer he gets his "5 o'clock surprise," an additional bill for a very expensive piece of plastic!
Since most intake gaskets must isolate, separate and prevent cross contamination of coolant, exhaust gases, oil and vacuum, we also insist that the engine installer take full responsibility for and warrantee their proper installation. Conversely, whenever we have a potential issue regarding engine warranty, we also insist that the engine must be returned to our shop for evaluation with the intake manifold attached and undisturbed. This was not always the case.
We supplied a 4.9L V8 Cadillac to a dealer with the intake manifold installed because we had the original intake and it was a convenient way to keep dirt from entering our rebuilt unit. Shortly after the engine was installed, external coolant leaks developed at the corners of the intake. We initially took responsibility and honored a labor claim for installation of another intake gasket. But subsequent events revealed that the cooling system was contaminated with black greasy deposits of block sealer, added in a misguided attempt to address the original problem of a poorly serviced and perforated aluminum block. Melted heat tabs revealed the intake coolant leaks occurred because the engine had been overheated and loosened the intake bolts!
For over a year, the driver/owner of a 351W propane powered Ford delivery van whined to his installer that the engine we had supplied was using oil at a steady, albeit low, rate. He had no complaints about fuel economy or performance. We, in turn, listened to the whining of the installer who eventually removed and returned the engine to our shop for evaluation. If our customer had removed the intake, we might never have ever found the problem. However, when we removed the intake, we discovered that both intake gaskets had been installed upside down, allowing a small amount of oil to be sucked into the intake. After more than a year and 56,000 miles km of oil injection-produced thick carbon deposits in the combustion chambers and severe valve seat recession, the engine had to be rebuilt again at our former customer's expense.
In 1996, GM redesigned the 4.3L V6 intake manifold and gasket. The changes in the orientation and size of the manifold bolts resulted in a reduction in the recommended torque and the effective clamping force imposed on the new gasket. GM has since advised that over-tightening the new smaller intake bolts may lead to block distortion and premature main bearing failure! Others have suggested that the new gasket, over-tightened or not, is prone to fail and allow coolant contamination of the oil, precipitating bearing problems. In my opinion, this situation is reminiscent of the 2.8L, 3.1L and 3.4L V6 GMC intake manifold gasket pattern failures (Automotive Rebuilder, 3-90) that began in 1980 and remain a common fault.
Anyone still want to argue that engines are more reliable and that the engine business is slow because of improved quality? When you add the problems associated with the introduction of the new alternative coolant formulations and the soon to be announced changes to all engine oil additives, it seems to me that a lot of effort, or lack thereof, is being directed at keeping dealer and independent bays busy with engine repair.
Don Fedak owns RPMS a machine shop located in Brantford, Ontario. firstname.lastname@example.org