Old engine (/6), Low miles, slight leak. What oil?

[dannyd]

I have a '62 Valiant with a 170cu.in. slant six. The car has only 13K miles on it and sat in storage (wet) from 1962 until 1987. The engine runs well but has a slight oil leak from, I believe, the rear main seal.
OK, do I use HM oil with seal conditioner, or stay with, say M1 10w30? Do seal conditioners cause havoc with other parts in the engine? I called M1 hotline and the person there recommended 10w-40 M1, but the owener's manual says 10w30 or 30 weight.
Sooooo, what do you think?

 

[94supraonchrome]

I'd use a straight 30 or 10w40...

 

[Steve S]

I am thinking the rear main seal is rope type seal and cork pan gasket? try h.m., oil won't hurt.

 

[bepperb]

Is fixing the rear main seal out of the question? I'm not sure the rest of the car's condition, but that's a pretty cheap and easy fix and at only 13,000 miles it seems if that's the only thing wrong with the engine, then it has 100,000 miles to go before a rebuild would be in the works, you might as well do it now.

If it's so slight you think a HM oil would do it, I don't know why you'd stray from 10w30. Shouldn't get hot enough in Seattle to go 10w40, and consuption doesn't seem to be a problem.

 

[dannyd]

Why would you use 10w40 in an engine designed for 30?

 

[440Magnum]

Use a good quality 10w30, synthetic if you want but not necessary. Also join slantsix.org if you haven't already- great resource for leaning towers of power. Don't be tempted by single-grade or heavier grade oils (20w50, etc.). The slant-6 is a really durable engine, but you can get in trouble by doing things that raise the oil pressure too high (like running thick oils...). The oil pump drive pinion is small and if you overload it it can wear out quickly or outright fail.

As for the rear main... are you SURE its a rear main? My money would be more likely on a valve cover that leaks at the rear and dribbles around/through the bellhousing and makes you think its a rear main. If it is a rear main, it might be worth the effort to replace it on such a low-miles engine. You'd be living with that oil leak for a loooooong time otherwise... ;-)

 

[TallPaul]

High mileage oil. My preference being Maxlife.

 

[94supraonchrome]

better protection and may stop that leak, friend with a 92 Camry has a slight leak, switcked to 10w40 2 oil changes later leak is gone, heck I'd even try 20w50...if it doesn't work replace that rear main...I'd use a ZPPD additive or an oil that has it already as well for that older engine.

 

[Volvohead]

Straight 30 or 10w30. Don't need a 40.

I'd be more comfortable with a conventional due to the seal technology. Rotella or Delo are good picks.

The older rope style split shell RM seals were prone to weeping even on thicker conventionals. Yours is predictably leaking. They all eventually leak. You are almost guaranteed a leak on a modern synthetic. It's not an oil issue. It's a 1950s-1960s seal design and materials issues. A modern seal conditioner won't fix it.

At least the RMS is easy to do. I can't tell you how many of those I've replaced over the years.

Drop the pan, replace the rope, and run Rotella.

 

[440Magnum]

Originally Posted By: Volvohead
Straight 30 or 10w30. Don't need a 40.

I'd be more comfortable with a conventional due to the seal technology. Rotella or Delo are good picks.

The older rope style split shell RM seals were prone to weeping even on thicker conventionals. Yours is predictably leaking. They all eventually leak. You are almost guaranteed a leak on a modern synthetic.


FWIW, I've never had a Mopar rope rear main seal leak, even at >>200,000 miles and on synthetic. If this one is leaking, its most likely from the extended period of sitting. It probably stuck to the crank and then tore slightly on restart.

But I still say its more likely a valve cover or other leak trickling through the bellhousing.

 

[Boomer]

And watch out for the exhaust valves. They are not the newer hardened ones and so you might want to run a lead substitute in your fuel.

 

[demarpaint]

Originally Posted By: Boomer
And watch out for the exhaust valves. They are not the newer hardened ones and so you might want to run a lead substitute in your fuel.


Good point, a lead sub, or TCW3 @ about 2oz-3oz/10 gallons of fuel, or MMO @ about 4oz/10 gallons of fuel should help with the valves.

 

[Volvohead]

Originally Posted By: 440Magnum


FWIW, I've never had a Mopar rope rear main seal leak, even at >>200,000 miles and on synthetic. If this one is leaking, its most likely from the extended period of sitting. It probably stuck to the crank and then tore slightly on restart.

But I still say its more likely a valve cover or other leak trickling through the bellhousing.


I GUARANTEE that if you reach up and wipe your fingertip along the seal/bearing cap, your finger will come away wet.

They ALL weep. Perhaps not dripping, but you'll always find a spread of film getting past the seal. It's designed that way. If the rope didn't let some oil weep past, the seal would burn up. It's a crummy design (glorified packing), but easy to assemble and repair in the field.

That's not to say that a Mopar engine of that vintage doesn't sport a gasket leak too. More did than didn't when I worked on them. High Tack can become your best friend with some of these.

 

[Steve S]

Originally Posted By: dannyd
Why would you use 10w40 in an engine designed for 30?
It doesn't matter.

 

[TallPaul]

Oh, come to think of it, I'd spike the oil with some extra zddp, or run Valvoline VR-1 which already has the extra zddp.

 

[Dupree]

I run 5w-40 rotella in my slant and she likes it. I would check valve cover first. Also if you are he** bent on 30 go with mobil 1 10w30 high mileage or rotella 10w30, either of these will be good with the slant (they have a good dose of zddp).

 

[dannyd]

And the winner is.....drum roll.....

440 MAGNUM!!!

--Tightened up the valve cover, and , voila! no more leak...(I hope...)

Next, the auto trans leak...somewhere in the back around the area of the shift(?) cable housing.

Thanks, 440, for your help in solving problem #1.

-Dan
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[jorton]

Originally Posted By: dannyd
Why would you use 10w40 in an engine designed for 30?


5w30 and 10w30 thin to borderline 20 weight oil, or thinner after 1000 - 2000 miles of use because they're "energy conserving" grades. That may be ok in your 62 I don't know.

If you're not sure about that either, use 30 or 5w-40 or 10w-40.

 

[ac_tc]

Hi, just wanted to add my wiev.
Been running my /6 on syn 15w40 hdeo for years.
Only draw back have been those really cold starts.
My new hdeo oil is a syn 10w-40 so thats whats going in next time.

 

[lewdwig]

I'd do an OCI with a high-mileage oil (10w-30 or 5w30) and then go to whatever you want (maybe Valvoline VR-1 or a HDEO).