I am looking at doing an oil change on an 1978 Corvette and need some advice.

I purchased this car last year, and the previous owner told me to always use 10-40 oil in the car.

I have read this forum a lot and heard very good things about Mobil1 oils, so planned on using that. However, I am told that Mobil1 does not make a 10-40 oil (or if they do, it is not readily available in this area).

This leads me to a couple of questions.
1) I was told by one person that 10-40 oil is to heavy for this climate (Minnesota). The manuals tell me that I can use either 10-30 or 10-40 oil. Is it true that I should not be using 10-40 oil?
2) If Mobil1 does not make a 10-40 oil, I can only assume that the oil this previous owner was using was non-synthetic. Would it be bad for me to suddenly switch to synthetic (and change the weight to 10-30)?

Car details:
1978 Corvette Pace
L-82 engine
61xxx original miles

Thanks for any advice you might be able to provide.
Andrew

 

I'd run a 5-30 in winter and 10-40 during your 2 month summer.

 

Run the Valvoline 10W-40.

 

In your climate, and considering the age of the Corvette, I would recommend using a good grade of 10-40 motor oil. I wouldn't use the synthetic simply because it is going to leak more than likely in an old engine. You are more than safe using a top quality 10-30 or 10-40 motor oil. I use Castol 10-40 in my 79 L-48 and it is perfect for here in Pennsylvania which is close to your type climate.

 

10-40 is good down to like -20. If the temp drops below that for a couple of days of not driving then you need an oil heater...they should sell them up there...either the blanket type, or an oil pan modified with a heating element inside. As for the lighter oil, here's an excerpt from Pennzoil.com:

7. Why do we really need lighter viscosity oils?

Most late model engines were designed to use lighter viscosity oils compared to older models, which required a thicker film of oil to provide proper separation of parts, such as main bearings from the crankshaft. Oil passages were larger to accommodate these thicker oils. To take advantage of the fuel economy benefits of lighter viscosity oils (SAE 5W-30, SAE 10W-30), late model "low friction" engines are designed with smaller oil passages and film thickness requirements. Lighter viscosity oils also flow much more quickly at engine start-up especially in cold weather. Severe engine wear can result if oil fails to circulate rapidly to critical areas. Lighter viscosity oils also circulate more efficiently through the engine and remove heat faster.

So, you see lighter oils will be good for newer engines, but if you have a stock engine then you need the thicker oil. What "manual" says to use 10-30? If it's your original owners manual, then read on...cause mine says to use 10-30 only in an emergency, and if you use 10-30 then driving at highway speeds (like 50mph or greater) could cause excesive engine wear. Keep in mind that even in colder climates your engine will get up to operating temperature, and at that temperature the stock engine requires 40 weight oil.

I would not recommend using synthetic in an original engine, nor do I recommend using 10-30. If you feel you need an oil for the colder climates then go with the 5w-50 that I'm sure is available up there. Anyway, isn't the cold weather over? Here in Washington State we are getting temps in the 70's.

 

Thanks everyone for the advice, it was very helpful. I will avoid the synthetic and stick with the 10-40 weight oil.

What is the consensus for what the best conventional oil and oil filter are to use, assuming I am going with 10-40 non-synthetic oil?

Thanks again.
Andrew

 

Any of the major brands are excellant choices, and I use a AC PF-25, but there are any number of good filters out there. Everyone has their own ideas.

 

Very easy, If you are not buring oil stick to 10-40, If you are burning oil then 1/2- 10-40 and the other 1/2- 20-50. Chances are you are burning at least 1 liter or quart per 1000 miles. Do the 50/50 mix

 

Don't get caught up in the brand of oil. As long as the oil as the API sticker, you're safe. Consumer reports did a big test on oils, trying to see if there was any truth to the marketing. There isn't. The cheapo stuff protected as well as the high dollar oils.

Synthetic is great for high stress applications, or if you live and drive in a very cold climate. But as others have pointed out, you do not want to start running synthetic in a high mileage engine that has not had the benefit of synthetic oil, early on. It will leak and smoke like crazy. Just to see if there was any truth to this, I tried it. And my car that did not previous leak, leaked like a mother. I switched back to organic oil, and it all cleared up.

Good luck with it. An oil change is a good way to get your feet wet, with mechanical sort of things.

Make sure you remember to put the new oil in, before you start! And make sure you rub a little bit of the old oil on the threads and gasket of the oil filter, before you install it.