Got over 200k on this 4.3l vortec. Just bought it and haven't gotten into it much, so don't know the repair history of the engine.

I've read that the 4.3l's will develop some sort of intake leak around the 200k mark, and will ultimately destroy the mains and kill the engine.

My question: Is it worth it to switch this engine to synthetic? If so, should I go with a higher viscosity? (btw, I'm in Michigan) Any recommendations to get this puppy to 300k?

Any recommendations, personal experience, etc.. is much appreciated!

Thanks ;-)

 

Intake leaks? What do you mean by intake leaks? I do know these engines are notorious for there lower intake manifold gasket leak and that happened for me around the 100,000 mile mark. The problem is the intake manifold is aluminum and the engine block is cast iron, which expand and contract differently. If you can repair your own vehicles, the part is not that expensive to get, just a lot work involved of tearing it down to get to the gasket. Otherwise, its about a $500 job at the garage. Make sure you get the manifold gasket that has the metal in it. Otherwise, I don't know if you are referring to another area or not. Being if that's the problem, the answer is no, switching to synthetic will not solve your problem. Coolant will leak into the engine oil and of course there your engine failure. First thing is fix the leak in your intake, then if you want to switch to synthetic, then you can. I know some people might have a different opinion on this, but I just change my Blazer to Mobil Super High Mileage oil and it stopped a small oil leak I had. Yes, it may be temporary, but I hope it last as long as have the Blazer. If you have some minor oil leak and want to go fully synthetic try the Mobil 1 High Mileage oil.

 

Its up to you, I always run Synthetic, I use the weight that the truck calls for 5w-30.
High mileage oil is a gimmick, and not worth the money. The things that are in high mileage oil can swell seals up too much causing them to crack, since there is no stopping them from swelling since the additive causes them to swell.
Once they start, they keep going.

I would stick to either conventional oil, or synthetic.

 

I have run full synthetic in my GM Rebuilt Long Block since I changed the engine in 2003. I now have over 100,000 miles on the engine and the engine runs like new. I am also suspicious of the long mileage full synthetic but I have nothing to base it on other than my gut feeling. I use Mobile 1 5W-30 full synthetic.

No leaks anywhere.

 

I know I touched the high mileage oil hot potato. All I said is it have worked for for now, but I am not going to be here say how great high mileage oil is. At 200,000 miles and not knowing how old or repair history of your engine, high mileage oil may or may not work. Its your call. Same if you want to synthetic. Asking if it worth it to use a synthetic on what you describe, my opinion would be no. Not knowing the repair history or else maintenance history, you don't know whats started going bad and synthetic probably won't stop it from breaking down. Secondly, this engine if been maintained would be able to reach 300,000 miles on conventional oil. Besides an intake leak these engines are reliable. They basically are minus 2 cylinders of a GM 350 v8. But its up to you if you want to use synthetic. Also about going to a higher viscosity and being in Michigan, I would stick to the 5w30 if you are not losing too much oil.