home > tech tips > bruce's tips > engine corrosion

Engine Corrosion

a) Like the 944 4 cylinder engine, which shares many common parts, single cam and twin cam 944 models, the 928 models engine blocks have proven to be very corrosion resistant.

The cylinder heads are a different alloy though, and are more prone to corrosion.

b) The 928 4.5 and 4.7 single overhead cam engines are not at all prone to head gasket problems. That is, coolant leaking into combustion chambers or oil galleries or vice versa, providing the coolant mix is changed every two years. If that is done from new, they have almost no corrosion.

Iím talking about Sydney conditions. I donít know about other locations or the condition of water used. 

For example, South Australia has water very high in minerals, and even if an owner tops up from time to time with tap water, a problem could occur over a long time. Iíve had some heads off these engines because of excessive oil leaks from the head gasket, the oil gallery passes (oil under pressure) on cylinder bank 1 to 4 near cylinder 4 on the exhaust side and on cylinder back 5 to 8 near cylinder 5 on the exhaust side.

All of these cars were ex company-directorsí cars that for the first 3 to 5 years sat in heavy traffic every day. Under those driving conditions everything in the engine and engine bay gets fried i.e. oil seals, wiring harnesses and head gaskets go hard and age quickly. So when they get to 15 years of age they have oil leaks from places that just donít seem possible. In other 928s of the same age, but with different upbringing, a totally different result is seen.

On these 'oil leakers' with the heads off, 13 to 20 years old I have seen no corrosion around the tops of the cylinders and at worst only slight corrosion inside the heads - in other words very fixable.

In another case I had a 944 single cam MY '83 that had a classic case of coolant in the combustion chambers and at over 265,000 km, I removed the head and found it heavily corroded but the engine block luckily still in good condition. I discovered this engine had been running on just straight water for over 3 years.

Donít do this!

The ones that have had corroded cylinders would suggest to me either a lack of coolant changes (i.e. ex Hong Kong cars for example)

c) Same thing applies to water pumps, when removed. When replacing the cambelt etc. I have never seen a water pump impeller ever go near the machined corresponding section of the engine crankcase. Usually just the opposite, with the impeller usually wears into the water pump housing if in a bad way.

d) I havenít any oil leaks from the quad cam head gaskets 5.0 or 5.4 litres. But have seen a few (lot) of cam cover seals leaking oil externally down the side of the engine. But also into the spark plug holes, which fill up with oil, so when you remove the plug lead suppressor/connector, itís soaked in oil which also wrecks the soft end-push on the sleeve that is part of the suppressor/connector.

e) Last note on corrosion. On the ones with poor coolant change histories, they also have corroded heater pipes (on the near side of the engine bay) and heater cores and radiators. (e.g. Hong Kong cars mainly). Look at the condition and amount of corrosion on these easily accessible header pipes as an indication. The ones with regular coolant changes over the years = no corrosion at all or very little.

Buchanan Automotive
Unit 2/2 Paton Pl, Balgowlah NSW, 2093
(02) 9948 2651