engine rebuild and synthetic

[willfxp]

if i rebuilt an engine would it be good to switch to synthetic? i hear that synthetic isn't good on an old engine (180k miles) because its thiner and would get into cracks and start leaking. but if you rebuilt an engine it would replace all those seals right? so it might be good to switch over? tia

[Mule]

The synthetic leaking "story" is that it cleans/scrubs the inside of the engine. So if you have little leaks held together by goo or debris, it may get scrubbed away and create bigger leaks.

 

If the engine is rebuilt without leaks, the synthetic will not create them on it's own. Now, depending on what is rebuilt, there may be some wisdom in using mineral for the first few hundred miles to help things break in.

[Import Hater]

The majority of professional opinions are to start an engine off with dino oil then switch to syntehtic on the 1st change.

 

My personal feelings on the matter is that as long as you build it right, I would think most modern engines can run synthetic right from the get go. Corvette, Mercedes, Porsche, and several other new cars come with synthetic on the factory fill. Brand new never fired engine has synthetic oil, with the blessing of the factory. That should tells me all I need to know right there.

 

Rob

[superbee]

In modern factory engines, the parts are CNC machined. Computer controlled machining, if you will. Using low tech methods of rebuilding, ie your average local machine shop/ parts store, the tolerances are not nearly as close as the factory builds. Using Dino oil the first 1000 miles is said to make sure you wear the sharp edges in quickly. Using Synthetic oil will take longer to wear said edges and may consume (combust) some oil until the break in is complete. I have done both. I have decided to use petro oil to break in my rebuilds for one reason. It is cheaper. When an engine is assembled for the first time at your local machine shop, or in my case in my garage, moly assembly lube is applied to the camshaft and bearings during assembly. I always run the oil pump with a drill for 3-5 min to bathe everything. On first start I run for 15-20 min at idle to break in the cam. Stop engine, drain oil, change filter. Drive for 100 miles, repeat, run for additional 400 miles, repeat. Run for 500 miles, switch to synthetic. I change the oil so often that it is not economical to run synthetic any sooner. I like to get all of the assembly lube flushed out as soon as possible. Many people will have different opinions. Good. I have yet to have an oil related failure in any of my home built engines, road or racing. Oil is too cheap and engine parts are too expensive!! If in doubt, dump it and pour in fresh oil!! Your engine will love you for it!!

[willfxp]

Thanks for the tips! Burn in idea with dino oil sounds better since it's cheaper.

 

This would be our first time rebuilding an engine