Id try Mobil 1 high mileage 5w-30 . It is a very good oil with a very stout add pack , with some seal swelling properties that I think your civic would benefit alot from. It could be Mobil's best oil , it has a high flashpoint with a very low pour point as well .Its a stand out oil.
Execut1ve, I don't agree with this suggestion at all but you'll get lots of "out in left field" personal opinions on this website you'll have to sift through. It's not their best oil and the PP spec' is useless to your application.
My suggestion is not a "out in the left field" personal opinion. He said he was interested in a synthetic oil that would work well in his car. I never said it was Mobil's best oil rather one of their better ones. He needs a oil that would provide low and high temp protection and M1 HM will do that. M1 HM is thicker in viscosity than your average 30wt oil but it is not nearly close to being thick as a 40 wt. He lives in Ohio where summer time temps spike above a 100 degrees, why should he put in a 20 wt oil when 30 wt has done well for 234K . Just because Honda says you can use a 20wt does not mean thats the ideal oil for a well broken in engine in 100 degrees.When I said M1 HM was a better mobil oil,all you have to do is look at the add pack and it speaks for itself. I think M1 HM 5w-30 is an appropriate suggestion for a car that I think anyone would classify as a high mileage car for a owner who is thinking about using a synthetic oil in a 5w-30 grade oil.
No offence, but I don't agree with anything you've said.
I'm not a fan of M1 HM 5W-30 for many reasons, but one is it's low VI of 162 which is even lower than the regular M1 5W-30, the latter of which meets Honda's HTO-06 spec' and the HM version does not.
M1 HM 5W-30's HTHS vis of 3.4cP is undoubtedly more than the OP needs, but even if he did want an oil that thick a 50/50 blend of M1 AFE 0W-30 and M1 0W-40 will achieve the same thing but with a far superior VI of 182.
Even though the OP's Honda has a lot of miles on it, that's no reason to automatically assume a heavier than specified oil is necessary. Only if the engine's oil pressure was on the low side would a heavier oil be warranted or if his oil consumption was excessive.
You dont have to be a fan of M1 HM , doesn't change the fact it is a very good oil .As far as the difference between a VI of 162 or 182 , his honda will never know the difference. Im not assuming that because he has high mileage that he needs a thicker oil at all, however his honda will benefit from the slightly thicker oil at summer time humid 100 degree temps seen here in the U.S . M1 HM is also beneficial in this application due to the seal conditioning agents in the oil.Even if he has no consumption and normal pressure it will only help the car from preventing these problems in the future. Im not saying he HAS to use M1 HM , just that it would be a good oil for his car. I have used this oil in my fiancee's old 91 Honda accord which had 285K with saw -20 in the winter in WV and which saw summer temps of 105 in SC. The oil performed excellent until the we donated the car due to a rusted out body. Execut1ve use whatever oil suits you car , my suggestion as stated before is M1 HM , it served my fiancee's high mileage Honda well and would serve yours well.