Were the heck is my oil going?!?

[Randog]

Howdy,

My 1973 Datsun 620 is losing oil. Like, lots of oil. Its gets 22 miles to the gallon gas and 40 miles to a quart of oil. I haven't for the life of me been able to find a leak. I have changed the PCV valve, and with the exception of the main seal, all oil gaskets and seals on this engine are new. Unfortunately, I really have no idea how many miles the engine has, but I do know that it is not the original engine and the odometer says 140,000. It has plenty of power, and while it does blow out a small puff of blueish smoke when I shift, I would think for a quart to be gone in 40 miles I'd have to be billowing out clouds of blue smoke constantly and badly, not just a little puff. And I would probably foul my plugs, to. Anyone know what could be wrong?

[datsunaholic]

That little puff of smoke is enough to know it's burning it. I've got one that burns a quart in 100 miles, and virtually no smoke at all. Modern oil is so thin and so "anti-pollution" that it hardly smokes at all when the engine is running hot enough.

[zed]

the oil must be going somewhere, if it's not being burned. Are there drops on your garage floor or driveway? oil on the underside of the car from leaking engine oil being blown back from the motor while you're driving? I have that on my Hardbody truck - my main cap side seals are leaking I think. Maybe try laying under the motor while it's idling and look for a leak? Are L-motors very tolerant of oil use?

[Zeusimo]

http://community.ratsun.net/topic/28804-how-to-replace-valve-stem-seals/

[Randog]

The truck can sit in the shop over night and no oil on the floor. I was just out there, I looked at every oil seal and gasket I could find and couldn't find a leak. I forgot to pull the plugs out and see if there were fouled. Not sure what you mean by tolerant of oil use. And what about before the truck warms up? I don't let it sit in my driveway, I start up and go, still not much smoke. Maybe it is being burned, but it just seems to me that a quart in 40 miles is a LOT of oil to just burn, and not hardly see any blue smoke.

 

So, Zeusimo, there is no way to change the seals without taking off the timing chain and camshaft?

[ggzilla]

Randy, it is burning the oil. Once you see any blue smoke, it's all over. Most smoke people never notice. You can double check it if you want by doing smoke tests.

 

Time to throw a new set of rings in it. You won't need new pistons or need to bore it. Just fit new rings (overhaul).

[Randog]

So I can't even just get away with changing the valve seals?

 

Where do I get new rings?

[banzai510(hainz)]

I would pull off the PVC hose at the crank and smell that sucker or leave open then at night since a flashlite acroess it and see if you see the smoke. Or from the top valve cover vent. At idle should be more noticable

 

if running stock aircleaner assembly it will get sucked up and blown out the back.also if still using a weber set up.

Sidedrafts set up most run open crank case and youll notice a stick or smoke out from the hood

 

Where do I get new rings?

 

What you mean? where? there is the internet!

[datzenmike]

So I can't even just get away with changing the valve seals?

 

Where do I get new rings?

 

Try running a thick(er) 40w oil.

 

 

i I would definitely change the valve seals first. It's cheap and easy to do in a morning and without removing the head.

[ggzilla]

Valve seals rarely cause puffs of smoke when you drive. They typically cause smoke when you first start.

 

Have you done wet & dry compression tests? Start with the basics. Don't forget the basics! Don't listen to anyone from Ratsun without doing the basics and double-checking it yourself.

 

You can buy new rings from Nissan or Oreilly/Kragen/Grand Auto. But do you need them? Do a compression test (both wet and dry).

 

I hear there is a guy in Sacramento with lots of Datsun parts. Maybe just get a good used L-series four and swap it in?

[EricJB]

Smoke on exceleration= rings.

 

Smoke on decelerationm and morning start up = valve seals.

 

Does it smoke going uphill? (excel), or downhill ?(decel) Have someone follow you. And yes do a comp test.

[ggzilla]

Smoke on decleration can also be caused by the rings, not so much the Compression ring, but the 2nd and oil rings. If you remove the rocker cover and see some missing/broken/loose valve seals well then that's a big problem.

[Zeusimo]

Rev Motor

 

If Smokes For A Bit And Clears Out

Your Seals Are Bad

 

If Smokes Continously

Your Rings Are Bad

 

Some People Say There's A Special Valve Spring Removal Tool

But You Might Only Save 30 Mins Of Time

What's The Difference Between Removing Cam Or Not?

 

Just Change Your Stem Seals.. There.. What $15?

Do It In 2-3 Hours

[ggzilla]

"just replace the valve seals" is a pretty good idea. If the oil loss stops after that, you are done. And if it doesn't stop it, well at least you have new seals.

 

That diagnosis about revving is not very accurate. Bad rings can cause puffs or even no smoke at high revs.

 

Your test works well if the rings are way past worn, but not so well if they are partially worn. Rapping the engine and testing at idle is a better method, in conjunction with a compression test it covers most bases.

[Randog]

It smokes when I shift.

 

I got a great deal on a 720, it was practically given to me. I'm gonna sell both beat up trucks and hopefully clear up enough to buy myself one nice decent truck. My 620 is listed in Spokane Washington Craigslist, if anyone's interested.

[harlow426@msn.com]

<font size="5">Try eliminating pvc......<br>--connect a long (15-24) tube to the crankcase vent and stick the open end in a small coffee can w/ hole in lid. The manifold vacume may be pulling oil thru your valve guides if they are worn and/or if you have bad valve seals. Also....run 40wt single viscosity oil (harder to pull past rings/guides. Hope this helps.  Ive got a dynamite L18 in my 74 I will sell soon (low miles, original/not a rebuild). O!!!! Don't forget to cap off the port on the intake where you pulled off the hose/pvc.....if you don't you will have a major vacume leak(hard to start/run really lean/pop thru carb/burn valve/hole piston, ETC)<br></font>

[datzenmike]

<font size="5">Try eliminating pvc......<br>--connect a long (15-24) tube to the crankcase vent and stick the open end in a small coffee can w/ hole in lid. The manifold vacume may be pulling oil thru your valve guides if they are worn and/or if you have bad valve seals. Also....run 40wt single viscosity oil (harder to pull past rings/guides. Hope this helps.  Ive got a dynamite L18 in my 74 I will sell soon (low miles, original/not a rebuild). O!!!! Don't forget to cap off the port on the intake where you pulled off the hose/pvc.....if you don't you will have a major vacume leak(hard to start/run really lean/pop thru carb/burn valve/hole piston, ETC)<br></font>

 

Removing the crankcase vent hose won't stop the oil from disappearing or smoking. This motor has severe oil burning problems and blowby of burnt oil fumes needs to be vented from the block. Best the PCV system left alone. Do not block the PCV valve as the carb is designed to work with that known 'vacuum leak'. Closing it will throw the idle mixture off.