Synthetic vs Conventional for first 1000 miles

[rockdogz]

I plan on running Mobil-1 on my new engine, but have read in places that conventional oil is recommended for the first 1000 miles, then you can switch to synthetic. Anyone know why this is?

[gmachinz]

If your motor is all-aluminum, you don't need to break it in with conv. oil-you can use Mobil 1 from the break-in on. If this is an iron motor, then yes, you need to use a lightweight conv. oil for the first 500-1000 miles. I would use a 30W non-detergent. In an iron motor, the rings need to seat before switching to a synthetic-otherwise, you'll always have excessive blow-by.-Jabin

[rancherlee]

If your motor is all-aluminum, you don't need to break it in with conv. oil-you can use Mobil 1 from the break-in on. If this is an iron motor, then yes, you need to use a lightweight conv. oil for the first 500-1000 miles. I would use a 30W non-detergent. In an iron motor, the rings need to seat before switching to a synthetic-otherwise, you'll always have excessive blow-by.-Jabin

An ALL aluminum engine STILL HAS steel sleeves in it and the rings STILL NEED TO BE SEATED just like an steel block engine. Use conventional oil for the first 500 miles in ALL engines. I usually run it 20 minutes to break the cam in, change the oil, run it 50 miles, change the oil, run it to 500miles, then change to synthetic.

[rockdogz]

Why a non-detergent oil? The local auto parts guy said that all oils sold there had detegerents, and you'd have to go to some special store to get non-detergent oil.

[Steve25]

Napa carries 30 weight non-detergent motor oil on the shelf. This is commonly used in shop and industrial air compressors. I don't know that it is need or not. This is more an opinion judgement that probably means nothing. Some very well respected engine shops used to use transmission fluid to coat the cylinder walls and I believe transmission fluid has a very high level of detergent compared to motor oil. Some engine shops also use non-detergent 30 weight to coat the cylinders. What I am try to say is that there are many trains of thought and both produce engines that aren't affected by either method.

Also, yes aluminum blocks use iron sleeves so I don't know why the different suggestions, but many people will tell you to run conventional oil for between 500 to 5000 miles. I do know that most factory engines are now put in vehicles with factory synthetic oil so I am not aware whether these engines are tested or not with conventional or synthetic oil from the factory.

Heres my opinion: I use conventional motor oil for the initial break in of the motor (which lasts approximately 45 minutes). From there I drain the oil and change the filter and put conventional oil in again. I then recommend an early oil drain of around 2000 miles for the first time. From there I put a new filter on and use synthetic oil or conventional depending on what the customer wants.

I have gotten to test the various methods at a research center and we determined that the only reason to use conventional oil for the first times is more determined by how good the final surface of the honing procedure was done. Conventional oil produces more friction and helps the rings mate against surfaces that are less than completely perfect. You can get by just fine with synthetic oil from the start if the bore is perfect (when everything is bolted together), but I would strongly recommend using conventional motor oil for the first oil drain and the initial break in. An added benefit is that conventional motor oil is a lot cheaper.

Steve

Edit*** I might also add that after the initial break in and oil change, I drive the car do a series of procedures such as full throttle acceleration from 2000 to 5000 rpm's. After I stop accelerating, then I keep the car in the same gear and allow the engine to slow the car down. This cleans the sylinders and then overlubes afterwards.

[myclone]

Use conventional oil for the first 500 miles in ALL engines. I usually run it 20 minutes to break the cam in, change the oil, run it 50 miles, change the oil, run it to 500miles, then change to synthetic.

I do basically the same thing and no probs yet after a couple dozen engine builds.