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Old 06-12-2010, 11:49 PM
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Radiator Stop Leak found in oil

I've had issues with my 406sbc for a while now. Last year I pulled the heads and I found three cylinders on the left bank and one on the right with milky residue. The engine oil wasn't milky. I thought maybe my head gaskets weren't sealing because of my 11-1 cr. I installed new gaskets and have been driving the car the last few months.

I started noticing a miss on two of the cylinders that were milky. The spark plugs on those two cylinders were cleaner than the others and smelled different.

I started reading up on Bar's stop leak. I thought I could have some sort of minor leak in the block or heads. I poured the stop leak in the radiator and hoped for the best. A week later I changed the oil and I seen some of the gold flakes in my oil. My drain pan was dirty so I hoped I had spilled some stop leak in to it by accident.

I changed my oil again two weeks ago and I noticed a few more gold flakes in my oil. I now confirmed I have some sort of internal leak. I went to Harbor Freight and bought a leakdown tester. I couldn't come to any conclusions after doing the test. I thought I might hear bubbles coming from the radiator, but I didn't.

This has me baffled as I have tried several things and have gotten no answers. The oil has never been milky, so the leak couldn't be bad. I've never seen steam out of the tailpipes. I've done compression test and leakdown test with no culprits. One weird thing is, the engine will not start after it's warm. I've tried high torque starters, wrap, bigger cables and battery. I'm now thinking a little water could be causing it to hydrolock? Just a theory.

I'm thinking of yanking the 406 and building a 383.

Any ideas or suggestions would be appreciated.

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Old 06-13-2010, 12:07 AM
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It could be the steam holes on the decks are leaking, letting coolant seep into the bores. The steam holes are a common place for 400 sbc`s to crack.
This problem is usually solved by having king pins as they are sometimes called installed. You could snatch the head and inspect the steam holes near the offending cylinders. Then check the blocks deck for flatness. Also check the bolt holes, sometimes what is called a "tri crack" can occur, I seen this happen once on a friends 350. There was 3 seperate cracks from one bolt hole, one crack going to the coolant port, one crack going to the number 2 and 4 cylinders. The funny part was the engine didn`t skip, didn`t overheat, and didn`t show any signs of problems. The only issue it had was it was down on power, it also used coolant but very slowly, the plugs were cleaner than the other cylinders as well. You may also want to check the head deck for flatness.
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Old 06-13-2010, 05:25 AM
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I think this is the second or third thread in a couple weeks, mentioning of contaminated oil, or steamy exhaust...from a 400-block. This is why I don't mess with 400's anymore. Not only are good cores getting scarce, but the potential for failure with these blocks is high.

Any good machine shop will tell you to have the block magnafluxed...especially around the steam-holes/bolt holes. It's worth the extra money. If they don't, and you bore it (new pistons/rings, balancing, blah blah blah)...then end up with "milk", or a locomotive exhaust...that's money THROWN AWAY.

There was a thread recently, I think it was something like "383 or 406"...something like that. I was probably the only one that said 383...and THIS is why. I've seen enough 400 failures...I've thrown away 400-blocks because of multiple-cracks. If you've got the moolah to full-on prep the block, that's fine. But I'm betting most people on here don't. So don't...

You want big-number cubes, go with a big-block.
If your car can't swallow a big-block (and big-cubes are your main concern) time to get a car that can...
Otherwise, an affordable/reliable 350/383 is the way to go.

Last edited by a1supersport; 06-13-2010 at 05:34 AM.
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Old 06-13-2010, 01:21 PM
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no dont go with a big block go with a world small block and make a 454 lil block big inch less weight more hp there are other after market blocks out there to
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Old 06-13-2010, 01:32 PM
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oh and why in the hell chenge a progect over the engine
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Old 06-14-2010, 12:23 AM
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Thanks for the replies everyone.

I've had alot of problems out of this engine and it may be time for it to go. I went the cheap route and only had it bored, should have had it magnafluxed.

I have a 350 block so it looks like a 383 would be a logical choice. I can have the machine shop turn down my 400 crank to a 350's journal size.

Thanks again for your time,
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Old 06-14-2010, 09:26 AM
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Quote:
Originally Posted by 4speed57
I started noticing a miss on two of the cylinders that were milky. The spark plugs on those two cylinders were cleaner than the others and smelled different.
Are these cylinders next to the water crossovers?

Quote:
I started reading up on Bar's stop leak. I thought I could have some sort of minor leak in the block or heads. I poured the stop leak in the radiator and hoped for the best. A week later I changed the oil and I seen some of the gold flakes in my oil. My drain pan was dirty so I hoped I had spilled some stop leak in to it by accident.

I changed my oil again two weeks ago and I noticed a few more gold flakes in my oil. I now confirmed I have some sort of internal leak. I went to Harbor Freight and bought a leakdown tester. I couldn't come to any conclusions after doing the test. I thought I might hear bubbles coming from the radiator, but I didn't.
You should pressurize the cooling system w/the engine hot- warming it up fully w/the cap removed will be enough. Then leave it to see if the pressure drops.

There are other places where you can pick up gold colored metal flakes- the thrust surfaces of the thrust bearings, the bearings themselves often have a copper colored layer (although not always).

Quote:
One weird thing is, the engine will not start after it's warm. I've tried high torque starters, wrap, bigger cables and battery. I'm now thinking a little water could be causing it to hydrolock?
It takes a LOT of water to lock the engine. Just a little wouldn't do anything in particular.

More likely the timing or something along those lines.
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Old 06-14-2010, 01:21 PM
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Thanks for the help. I think Autozone rents pressure testers and that should be my next check.

The two cylinders that are missing are #6 and #8.

When I had the heads off back in the winter and noticed the milky substance, I could never figure out where it came from. The head gaskets looked perfect and nothing appeared out of the ordinary. Cylinders 4,6, and 8 had the substance and cylinder 5 also did.

I thinking maybe my deck surfaces aren't flat?

Thanks for your time
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Old 06-14-2010, 01:44 PM
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Quote:
Originally Posted by 4speed57
Thanks for the help. I think Autozone rents pressure testers and that should be my next check.

The two cylinders that are missing are #6 and #8.

When I had the heads off back in the winter and noticed the milky substance, I could never figure out where it came from. The head gaskets looked perfect and nothing appeared out of the ordinary. Cylinders 4,6, and 8 had the substance and cylinder 5 also did.

I thinking maybe my deck surfaces aren't flat?

Thanks for your time
Having warped decks could be the cause, like you say.

What head gaskets are you using?
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Old 06-15-2010, 02:43 AM
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I used a set of ROL head gaskets. The description said they were extended duty and good for 500HP. The gaskets that I was using on when I had the milky substance were Felpro 375-8364PT. I think the Felpro's are for stock to mild builds.

I may yank the heads again this week and see what's going on.

I'm almost 100% sure the gold flakes are stop leak. I've changed the oil several times in the last year and I never noticed the flakes until I poured in the stop leak.

Thanks for your time and help
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Old 06-15-2010, 03:26 AM
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Hope I didn't sound like I was jumping on you in post #3. If I did, I apologize.
But I really hope it's NOT the block. Hope it is something as simple as a head gasket. Even a warped or cracked head is better than a cracked block.
Quote:
Last year I pulled the heads and I found three cylinders on the left bank and one on the right with milky residue. The engine oil wasn't milky.
Do you remember how the gaskets looked when you removed them? That's a lot of cylinders to have residue. If it were two neighboring-cylinders, you could narrow it down. But three on one side, and one on the other...wow.
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Old 06-16-2010, 02:16 AM
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The head gaskets looked good when I removed them. They weren't stuck, they looked almost reuseable.

Here is a link from an older post that has a couple of pictures of my milky pistons.

406 sbc woes, blown head gasket and bad lifters

Thanks again for your time everyone.

Last edited by 4speed57; 06-16-2010 at 01:49 PM.
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Old 06-16-2010, 01:51 PM
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Quote:
Originally Posted by a1supersport
Hope I didn't sound like I was jumping on you in post #3. If I did, I apologize.
I didn't think you was jumping on me at all.

I appreciate your help
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Old 06-16-2010, 02:07 PM
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My experience is 400's HAVE to be decked when rebuilt, either to just clean them up and provide a flat surface or to deck to a specific piston to head clearance, ...but it has to be done. They tend to sink the head surface between the cylinders .002-.004", too close to the operational limits of the composition gasket, regardless of whether they have been run hot or not.

If any cylinders that looked steam cleaned before are now better, or fine, after you made the first head gasket change then that fact would rienforce this as a place to check for problems.
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Old 06-17-2010, 02:46 AM
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Thanks for the reply Eric.

I guess I need to yank the heads and see what I have. After that I may be paying my machine shop a visit.

Thanks for your time,
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