Porsche 928: Why is There Oil in My Coolant?

Oil and coolant should never be mixing. If it is, then this is definitely a bad thing. This article will go over the most likely problem causing this sort of issue. So continue reading to find out why there is oil in the coolant of your Porsche 928.

By Arthur Guerrero - April 29, 2015

This article applies to the Porsche 928 (1978-1995).

Oil and coolant mixing in any car is a bad thing. A problem like this should be diagnosed and fixed as soon as possible. A problem like this has only a few potential reasons. Some of the reasons are more likely than others. This article will go over the main problems that can be causing your oil to enter into your cooling system.

Step 1 – Do you have a bad head gasket?

A bad head gasket is the most common cause of this type of problem. The gasket seals the area where the head cylinders meet the block. Over time, this seal can wear out (usually from overheating), causing oil to mix with coolant. This is usually the first thing a mechanic will check. These jobs are tricky to do because the gasket has to be replaced, and the heads have to be machined properly to ensure good fitment, so that this mixture doesn't occur again. This job is also pricey if you have a mechanic do it, and even more so if you take your Porsche to the dealer.

Figure 1. Head getting cleaned before installing new gasket.

Pro Tip

Make sure the mechanic you go to knows what they are doing. If you're not sure of their track record, you might want to take their diagnoses with a grain of salt.

If your head gasket checks out, move on the next step.

Step 2 – Do you have a leaking oil cooler and/or lines?

In the 1990+ models they have external oil cooler lines positioned above the radiator. Whenever the oil cooler lines would spring a leak, Porsche noticed that the oil would leak onto the radiator and cause a potential mixture. You can visually check the oil cooler lines for cracks and leaks.

head gasket
Figure 2. When you hear 'head gasket' and 'milk chocolate' in the same sentence, this is what they are referring to.

Pro Tip

There are pressure tests available to test out your oil cooler.

If your oil cooler and lines check out, try the next step.

Step 3 – Do you have a bad radiator?

Another potential problem that occurs with the 928 models that can cause the oil to run through the radiator is an internal crack. If this is the case, you would have to get the radiator replaced. You also have to replace the radiator hoses if oil got in them because the oil can cause them to eventually get damaged or cracked.

Figure 3. Radiator overflow contaminated with oil.

Pro Tip

There are external oil cooler upgrades that you can do to avoid this potential problem.

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