Where should I start???? engine smoke -

[86project]

I have an 86 C10 305 - 160K+ - Here's some background info - The truck starts with a lot of smoke - after about 5 mins of idling - the smoke goes away.  It appears to be bluish so i assume this is oil that is leaking past the valves. It runs quite rough until it is warm. It seems to like higher RPMs.....it will not idle without using the accelerator until it is warm.  After it is driven, and sits idling like at a drive thru, it starts smoking again but not nearly like at start up.  My initial thoughts are to buy a set of rmfd heads to see if this solves the problem, but with this many miles on the bottom end, is it worth it?  Could it also be bad rings?  Is it worth rebuliding a 305 or should i just wait and look for a 350 if the head replacement isn't a good idea?  Any suggestions, ideas, or diagnostic procedures etc are appreciated - 

[choptop]

run a leak down test on the cylinders if you have a leakdown gauge,. This will tell you whats leaking. I had a 350 in the wifes truck w/ 275000+ miles on it, so I yanked it. (Of course the 400 hp 355 on the engine stand helped the motivations a little) When  I pulled the engine down, the main thing was valve guides and seats. There wasn't even alot of where in the cylinders. My engine would foul the plugs when idling in traffic for to long. Other than that it did the same thing you are describing. I would rework the heads first, unless you have a power upgrade urging you on..

[86project]

Well the urge is there for the power upgrade but the funds aren't.....so I guess I should start with the leakdown test....I don't have a gauge but I think they are fairly inexpensive at most auto parts stores (you think the gauge is available on the "loan a tool" service?)

I guess I'm concerned b/c I've heard that I may be better of buying a 350 rather than putting the time,effort and money into fixing a 305 with that many miles on it-   Thanks for the advice -

[86 chevy silverado]

A leak down test is for checking loss of compression in the cylinder. Smoke at start up (blueish) is valve guides,  blue smoke under load is rings.

[86project]

so the leakdown test is basically to see if there are also bottom end issues (like rings) right? 

[86 chevy silverado]

It will help diagnose where any compression loss could be. you will hear air leaking through your exhaust for a bad exhaust valve, air though carb, Intake valve, air in oil fill or breather area, rings. You will see the gauge on the tester reflecting any loss of pressure.

[VileZambonie]

86 Silverado hit the nail on the head there....the leakage test is only for cylinder sealability not for oil consumption. Bottom line junk the 305 and upgrade to a 350 and live happily ever after

[choptop]

I have used the leak down test for troubleshooting for years. When you pressurize the cylinder, at that time if you listen and look it will tell you loads of informatiom. Bubbles in the radiator= head cracked or geasket, air leaking through carb= intake valve burnt= exhaust air leak = exhaust valve, air sound from valve cover= valve guides. 86 Silverado explained what I neglected (Thanks  by the way)It does work, you just have to turn the radio down. Air leak through valve covers,or through carb both indicate a good source for oil consumption. Where the air is coming from will tell you heads, or rings. My best guess since it goes away when it warms up , and only comes back when idling, tells me valve guides and seals. It is possible to replace the valve seals without removing the heads, and installing the umbrella style seals, but this is very tricky and on false move can be a nightmare, but it is possible. I bet Vile or Capt know the seal part numbers, but with that amount of mileage, valve guides is probably the main issue and just replacing the seals will only be a bandaide. If the motor is gone, a 350 will be the same cost to build as the 305 if not cheaper, drops in no problem, and makes life wonderful. Best of Luck

[86 chevy silverado]

I did forget bubbles in the coolant for a bad head gasket, between all of us we can get it right.

[choptop]

Thats what makes this site so great, no one knows it all, but all together we got it made.

[86project]

Thanks guys - I appreciate the effort and I'll update when i find out more -