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Porsche: Air Cooled Engine - Thermal Performance

Thermal performance for an air cooled Porsche engine is measured in how well an engine sheds heat. Obviously the cooling fan plays a major role in this heat-shedding process but there's more. Integral to the effectiveness of a Porsche engine's fan forcing ambient air over the crankcase and down through the cylinder fins and oil radiator is the thermal performance of each of those engine areas. Thermal performance meaning the ability of any given engine area to transfer heat away from the engine. Grime build up from oil & debris on an engine's exterior is the enemy---it serves as an insulator that degrades efficient heat transfer. Over time, this insulation can build up to a point where an engine's thermal performance is compromised beyond acceptability. Depending on the driving conditions an engine is subject to, thermal performance decline may or may not be easily noticed. Engines that experience stop-and-go traffic offer greater opportunity to detect thermal performance decline due to sitting repeatedly at idle.

Assuming a properly working temp sensor and temp gauge, a Porsche engine with optimal thermal performance can sit and run at idle (in roughly 80 degrees ambient) indefinitely and never will the temp indicator rise much above the bottom box or 210 dF or 90 dC. A Porsche air cooled engine with compromised thermal performance is indicated by an engine sitting and running at idle with its temp indicator progressively climbing into the red zone box. >> Prior to an indicator entering the red zone box, an engine should be turned off and allowed to cool prior to restarting. Opening the engine compartment lid facilitates cooling. << The faster a temp indicator climbs... the worse an engine's thermal performance is.


There are 2 fundamental benefits gained by preserving an engine's thermal performance:

1. Cooler engine operation preserves engine oil viscosity. Viscosity basically refers to oil's ability to lubricate/protect and so preserve an engine. An engine that consistently runs at a higher temp degrades its oil's viscosity faster and so sooner than a cooler operating engine. To remain on par with a cooler running engine, a hotter engine requires more frequent oil & filter changes. The absence of attending oil & filter changes more frequently in this case translates into premature engine wear. Bottom line: given all things being equal but for thermal performance, a cooler running engine will outlast a hotter counterpart.

2. An engine with poor thermal performance that's caught in stop-and-go traffic is concerning. In this circumstance, a driver should constantly monitor engine temp and consider options to prevent the engine from overheating. For any driver interested in their engine's well being, this is an annoying situation at best. Worse would be to ignore engine temps entirely. Doing so can be an expensive proposition---one best avoided by ALWAYS & CONSISTENTLY scanning gauges for engine status and taking intelligent action to preclude the unwanted.


We'll look at this from 2 perspectives. The first is restoration of thermal performance. The second is preservation.


Porsche's air cooled engines are notorious for leaking oil. Unless cleaned regularly, that oil will collect road debris and create unwanted insulating value over time. Where mild oil & debris build-up exists, degreasing an engine is a restorative process that can return adequate to optimal thermal performance to a Porsche air cooled engine.

In cases where oil-debris build-up has reached significant proportions, degreasing will work only partially (as is evidenced by repeated applications of degreaser failing to cleanse a surface to bear metal.) In such instances, oil-debris has baked onto the engine's surface forming a gelatin insulation and sometimes even a hard crust. Any accumulation of this nature between cylinder fins prevents cooling air (as provided by the cooling fan) from extracting heat from the engine as it is designed to do. Instead of exiting, unwanted heat radiates throughout the cylinder assembly outwards to the heads an inwards to the case... ultimately to the engine's oil. The more heat imposed on oil, the sooner its viscosity degrades.

In extreme cases---where degreasing is ineffective---one has to evaluate how best to clean a given engine. The best option may be to remove the engine from the car---this being required in order to gain necessary access to otherwise inaccessible areas. Compared to using a degreasing agent, more aggressive options are pressure cleaning, dry ice blasting, and media blasting to name a few. Each has advantages and disadvantages according to a given engine's situation. Optimal results are achieved by skinning an engine via media blasting. Skinning refers to cleansing a metal surface down to genuinely bare metal. Typically this is done with walnut shell particles blasted through a control nozzle under high pressure. Expert care is required where preparing, blasting and post cleansing is concerned.


Where the cause of thermal performance decline is not attended---continued oil leaks being the primary cause---engine cleaning on some routine basis is called for in order to continually preserve thermal performance.

Given the variety of covers, gaskets, hoses, clamps and oil related passages an air cooled Porsche engine has, it's impossible to offer advice concerning where oil may be leaking from in one engine compared to another---each engine can leak oil differently and to different degrees. The objective in regard to optimal thermal performance preservation is to minimize if not halt all oil leakage... and do so with the intent of keeping an engine as oil tight as possible for as long as possible.

Prior to proceeding with any cleaning of an engine where oil containment is an issue to be dealt with, it's of value to inspect the oil-grimed engine before cleaning... the goal being to ascertain any and all areas of particular interest---discerning where the oil's appearing most and where it's not. This intel serves not as a definitive conclusion about an engine's oil leak status, rather, it provides reference that highlights areas of special interest.

Some oil leaks can be attended without having to remove the engine from the car. Others simply cannot. To what extent an engine is to be resealed is always a decision affected by other attention an engine may require.

A perfectly sealed engine is possible, however, due to repeated expansion and contraction and the wearing of seals and gaskets from heat... an air cooled Porsche engine will eventually begin to weep oil at some point in time from somewhere.

Inspecting an engine from above and below on occasion is always a good idea. The more familiar one is with an engine the better equipped one is to care for that engine. Where preservation of thermal performance is concerned, it's better to degrease an engine often and remove minor build-ups as compared to degreasing less frequently and having major build-ups to deal with.


GP AutoWerks offers complete services in the areas of thermal restoration and preservation. It all starts with a complimentary inspection and analysis of your engine's status. With the intel we provide you---there's of course no obligation on your part---we'll gladly provide a budget for whatever you want accomplished. Want some complimentary tips?...give us a call. We'll provide you some important info so you can DIY if that's your preference.

For a look at the scope of our services, you're invited to visit our website: Services


This engine provides good reference for better understanding thermal performance of a Porsche air cooled engine. In this engine's case, when sitting at idle... the engine's temp would---if allowed to---quickly climb into the red zone. Being caught in stop-and-go traffic was annoyingly avoided by the owner at all costs.

The spread of oil here is prolific. On top, evidence suggests the breather and valve covers to be areas of origin. Underneath...oil sump cover, valve covers, return tubes, chain housings, main seals and intermediate cover appear guilty.

Degreasing this engine while it's in the car would be better than doing nothing however, given the condition of gaskets, clamps, hoses, seals, and o-rings... this engine's not a good candidate for degreasing. Were that path taken, it would not be a lasting solution---much like a band aide on an open artery wound. Essentially this engine is leaking too significantly for minor attention. Of major import is the fact that oil has streamed down from above and through this engine's cylinder fins. Where a Porsche engine's thermal performance is concerned, this cylinder status is very concerning. Essentially oil cooks and cakes up between the fins and progressively obstructs air flow. Hence, only by maintaining higher rpm does an engine in this condition cool sufficiently.


Every engine and every owner operates under unique conditions. Valuing this from the beginning is important when considering what course of action to take---doing things in cookie cutter mode lacks valued finesse to see the individuality of a given circumstance. In this particular case, what's most important is liberating the engine's cylinders from their accumulated obstructions and sealing the engine to cease it from continued leaking. These areas MUST be attended as priorities. There is no short cut here---the owner understands this.

Among options discussed, the owner opts intelligently to media blast the engine. Pressure cleaning will not work and dry icing will not achieve the optimal results as will walnut shell particles. >> It should be noted that blasting an engine with any media requires meticulous preparation---certain parts of an engine need be protected from the media. And all portals must be sealed correctly. No media is allowed to enter the engine. Blasting in itself is an exacting process---too much force applied in a single area can cause damage. Upon completion of the blasting process, meticulous cleansing of the engine is necessary to remove all blast media that would otherwise adhere to the engine were it allowed to. Particular attention must be paid to all crevices and all seams between the engine and seals installed for the blasting process. In a nutshell, media blasting an engine successfully requires specialized knowledge and skill. <<

The metal's surface that has been cleaned here is almost like new. "Almost" referring to the fact that on a molecular level, some oil/debris has been forced into the metal's surface. Of course this cannot be seen with the naked eye---nor does it matter. What matters is the metal being significantly liberated from the insulation that previously covered it. Most importantly being the removal of baked-on-crud between cylinder fins that previously inhibited adequate airflow passing over the entire skin of the cylinders.

Before removing seals that protected the engine from particle intrusion, the engine is meticulously cleansed. While seals are removed, great attention is paid to the process of separating a seal from the engine so that any particles residing at the seal's seam with the engine accompany the seal when the seal is removed.

After blasting and proper post-blast cleansing, this engine's being disassembled for further factory-spec inspections and work. Notably, and in regard to this engine's thermal performance, all its oil related sealing will be attended. Significant amidst this attention is the careful and thorough cleaning of all mating surfaces that will embrace either a gasket or o-ring.

The engine's now in assembly mode. Factory specifications are followed throughout the process. Not only does this mean accurate standards being applied, it means any future work done on this engine will have a factory-based reference to consider. This is of considerable value for any professional mechanic attending this engine in the future.

This case demonstrates the high end of what can be accomplished in regards to restoring thermal performance to a Porsche engine. Compared to when this engine was encased in oil-debris insulation... and could sit at idle for only a short period of time before its operating temperature would exceed reasonable limits, it can now sit indefinitely at a running idle with temp indicator rising only slightly above the lower box. This condition is recorded in 80 degree ambient temp.

Above. Before-and-after reference to the sample engine. While outward appearances are impressive in the final result, what matters more to the lasting performance of this---and any engine---is the work accomplished inside from beginning to end.

Need help understanding your Porsche engine's thermal performance? Give us a call---we'll be glad to assist you (305) 588-0874. You can also go through our website to learn more about our range of services


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