305 life expectancy


Junior Member
how many miles do they average before rebuilding time?
got my truck used 67000 miles i now have 94000 on it.
i had no problems other than water pump and brakes.
dont use or leak any oil.or smoke.
seems like it was tooking care of.
i was told it had new timing gear in it
motor is clean untouched steel looks like factory
this is a 305 are they in 3/4 tons?
why is this motor so bad on gas to much truck?


Senior Member
Lafayette, LA
whoa! Rebuild already?!?! Been running it without oil or something? Haven't you ever heard 100,000 is break in on a 305 or 350...it should be fine...if everything looks good and it runs good why touch it...a rebuild will more than likely not help your gas mileage that much...try a good tune up before a rebuild. Gas mileage usually is crap with a 8 305 shouldnt be that bad. What kind of gearing do you have?


Senior Member
Fairbanks AK
How long really depends on how you use it and how you take care of it. I had one (a 305) that was probably ready for a rebuild at 120,000. I've also had friends that make it to 150,000 and they still run like new. Sounds like yours is fine, from what you said. I think mine also wore out faster because it had to survive me driving it in my teens when I thought I had a 4x4 race car. Not to mention towing the boat, hauling fire wood, ect. You get the picture. Change the oil, take care of it, sounds like it's got lot's of life left.

mike reeh

Senior Member
regarding mileage, you said it.. too much truck..

had a friend with a 305 in a 79 suburban 4x4, it got terrible mileage.. dont make a whole lot of torque, but that motor should would rev to the moon


John DiMartino

PlowSite.com Veteran
Mike the 305 is not a great high revver,due to being a fairly long stroke motor.(as compared to 302 Ford)The 305 is a great engine for a car or 2wd truck,but in a 4x4 it is marginal,especially the 2500.I think if it is EFI,and is mainatined,200K isnt unreasonable to get out of one,they seem to be indestructable as far as durability.I would expect to be adding oil at that mileage along with it getting tired and a little smoke by then.My 350,which is the same engine,but with a 4.00" bore,as opposed to the 3.76 of the 305,has 146 on it now,and it plows and pulls-a lot.The hrs on it are probably similar to a truck with 175-200K on it.It does burn a quart between changes,but runs as good as new,The oil usage hasnt changed ,the valve guides are worn,a common problem with engines built at the flint plant.

[Edited by John DiMartino on 01-18-2001 at 07:46 PM]


Junior Member
1985 gmc 1/2 ton

i have a 305 with the valve guides worn , it uses a quart of oil between oil changes .it smokes a little when you first start it cold. it has 189,000 miles on it i change the oil and filter every 3 to 4 thousand miles or three times a year, once just before winter sets in ! it is not a good idea to run old oil in the winter. at 170,000 miles i change the water pump , the timing chain and gears,and the oil pump and shaft ,the 29 cent piece of plastic between the dist. and oil pump shaft ,broke one time on my 1976 chevy silverado and cost me a set of bearings!that piece of plastic can break any time after 7 years when you punch the gas. i replace the oil pump and the shaft with a high performance oil pump and shaft with a steel sleeve. :)


I have a 1994 s 10 with a 4.3 (same as a 350 just short 2 cylinders.) 140k on the clock and runs hard only reason that I am preping to rebuild is I want to add a cam and a couple other goodies to up the power a little
It is my daily driver and I can get 22+ mpg out of it plus it has enough to do most of my work if it can't I get the full size out that gets 8 mpg with tail wind well got a little off topic but any how keep your oil changed and wait till closer to 200k to rebuild or replace with a 350 at that time if you need more go