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Oil Change

I have a 2008 Cadillac CTS. I have a local shop change the oil regularly. Car runs great, has 65k miles. v6 engine. I had oil changed at the dealer recently and they said it had to have synthetic oil. I have only used conventional oil in it. Is this going to cause a problem?

Here’s what GM specifies for the motor oil for your car. “Use GM Standard GM4718 synthetic motor oil or equivalent”.

Probably won’t cause a problem in the short term. But use the oil specified by the manufacturer if you want the engine to last for the long term.


Read what it says in your owner’s manual. Make sure those instructions are followed. Not doing so can be costly in the long run. Some engines need synthetic and other’s don’t. Tester has given you the specs that the oil needs to meet. Makes sure you get it.

BTW never ever go to a quick oil change place. Not oily will not not likely get the right oil, but you have a good chance of a host of errors they tend to make.

If you have been changing the oil every 3000 miles(if all in town driving) to 5000 miles(mix town/highway) the likely case is no issues.

If you have been using the oil life monitor that tells you when to do it, you likely have caused excess wear or possible damage. The Oil Life monitor is programmed to use proper spec oil and is inaccurate with oil not meeting spec.

The only other major issue is if you hit a powertrain issue related to oil(rarer) and still under powertrain warranty(5yr/100k???), GM can deny your claim with good cause.

A friend has that model, I was surprised at the synthetic oil requirement when he mentioned it. That said, I would use it from now on. “runs great” doesn’t really tell you how well the oil was working. You’re probably ok, though. I would wonder why your local shop didn’t check on the oil needed for your car.

The possible worst case scenario with you having used conventional oil in your Caddy engine is that you have sludge built up in the cam chain valleys, or the valve cover area of the cylinder heads.

This can lead to oil starvation as the sludge grows, and restricts oil from getting to parts that need to be oiled, or from returning to the sump in the bottom of the motor.

That’s when you have oil starvation related failures.

A very high detergent synthetic oil should be used for the next couple of oil changes to help reduce the amount of sludge that may have developed. There might not be any sludge at all, but why run the risk?


Thanks for everyone’s response. I think I will take your advice and use the high detergent synthetic the next few times.