I just rebuilt a D17A VTEC engine to put in my 2005 Civic with 224K on it. The first and current fill that I plan to leave in for the first 600 miles for the break in is Pennzoil yellow bottle 5w20 because it was $3 a quart on sale and as I understand you cannot use synthetic for break in because it is too slippery for the rings to seat or something. My first question is how long I have to wait before I can switch to synthetic oil on a just rebuilt engine. My second question is what viscosity should I use FOR THE BEST PROTECTION? I do not care about a 1-2% increase in fuel consumption. I feel like switching to 5w30 will protect the engine better in the summer heat. The owners manual says to use 5w20 but I have heard that Honda only switched to 5w20 for a small fuel economy advantage, not engine protection. My concern with switching to 5w30 is that it might not flow well enough to cool and lubricate the parts inside the engine. Will 5w30 protect the engine better than 5w20? Thanks, I want my replacement engine to last as long as possible.

 

You should make sure to follow a proper ring seating procedure within the first 50 miles of initial startup. change the oil and filter right after seating the rings. and use a non-synthetic again. you can switch to synthetic after 100-200 miles of driving AFTER seating the rings. some may say 500 miles after.

oil viscosity is determined by bearing clearances, not protection. newer motors use a tighter bearing clearance which requires lighter oil. tighter clearance and lighter oil also makes more power, it's not just for fuel economy. using the wrong viscosity oil will actually cause less power, less mpg, and a faster wear. if all your clearances are within factory spec, stick to factory recommendation for oil as well. the best protection is not in the weight, but rather the quality of the oil itself. so just use a quality oil, and make sure to stay consistent with oil changes.

 

Thank you, just curious why the owners manual says to not change the oil when new until it is due. Is there a good reason to wait 5,000 miles to change the oil? Thank you, I want my engine to last as long as possible and run as good as possible during its life.

 

when a car is brand new, the engine already has several hundred or thousand miles on it. they break the motors in at the factory under very strict conditions before even installing into the car. and it gets fresh oil and filter upon install into the car.

 

Do you know your main and rod bearing clearances? If they are within factory spec, use factory spec oil weight. If they are looser, you're probably fine to run a slightly higher viscosity oil.