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Old 04-07-2020, 10:14 PM #16
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Originally Posted by G_Raw View Post
I did smell the exhaust yesterday but smelt fine, like I said I couldn't replicate it at the time. I then realized since im thinking coolant is sitting in a chamber and gets burned off I'd need to make the engine burn it...So started up today normal steam, normal exhaust odor. Revved hard a few times and steam starts to change to noticeable white clouds blowing while holding revs. No white clouds when i stopped revving . Revved hard and high and went out to take a whiff and it smelt dare i say like a sweet spice? Cinnamon...ish?

I know doing my valve covers are no where near the heads, but I was going to do water pump and timing belt. And at that point I am close to my heads, and would need to redo all those upper gaskets anyways.

It's one of those do I spend 500 to do VC and timing vs 1200 to do VC, timing, and heads. Or worse do first option only to do second option a few months down the road...
Here's my take on it. I'm at 385k and thinking the same as you. But in the end, if you are not actually using coolant, then you don't have a gasket problem. I have the same random puff of white smoke in the morning sometimes, but my truck does not use noticeable amount of coolant in the past 5 years since I replaced the water pump/tb. I have added about a quart of coolant in that time. I say just fix what you know is broken.

Save money for down the line, or do a block test if you are really worried about it. These engines run forever if you take care of them. I think most HG's go as a result of the radiator or WP leaking and running low on coolant and overheating. I was super worried about mine as I overheated it 1 time at about 355k, but the past 30k has been flawless.
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Old 04-08-2020, 02:07 PM #17
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I think most HG's go as a result of the radiator or WP leaking and running low on coolant and overheating. I was super worried about mine as I overheated it 1 time at about 355k, but the past 30k has been flawless.
My pet theory is that lack of cooling system maintenance is the problem - wrong coolant and/or not changing the coolant. If that's the case, the head gasket corrodes from the coolant passage side instead of the cylinder side.

Same deal with the pink milkshake - I took my radiator apart at 270k miles / 18 years old and it was *perfect* inside (no corrosion around trans cooler) - but the coolant was changed regularly (even though it was just regular green) through the life of the truck.

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Old 04-09-2020, 08:52 AM #18
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There's no doubt that poor maintenance (allowing coolant to get old and change PH and start corroding things) can cause them to fail. As can overheating the engine. And poinging/detonation.

But aluminum heads on iron blocks do scrub against each other as they heat up and cool down. They simply expand and contract at different rates. And the head gasket is caught between them and serves as the buffer. Ye olde style composite gaskets worked great for iron heads on iron blocks - the mating surfaces were machined a little on the rough side, and this clamped onto and locked into the head gasket composite material and it all stayed in place for a long time. And when they started sticking aluminum heads on iron blocks, initially, they used the same techniques. Which works fine for a certain number of heating/cooling temperature cycles. But eventually, you're going to scrub that HG into failure. Even if everything else is in great shape.

Eventually, they started using a different style of gasket - MLS. Multi-Layer Steel. And they make the mating surfaces of the head and block smoother. Now the head and block cerep and squirm against each other - but they're less abrasive. And the gasket isn't depending on a rough surface to lock in and maintain strength - it's a much stouter stack of steel sheets.

Toyota went through at least 4 revisions of HG's on the 5VZ, following a recall on the first revision when a lot of them had failures. Revisions 2 and 3 are still composite, but with larger metal surfaces on one side of the gasket. Revision 4 is the MLS version.

And really - you have to give credit to the rest of the engine here. Many other cars probably would have had similar issues - if they had alu heads on iron blocks, but they tend to hit junkyards earlier. The 3.4 just keeps on going until more subtle design issues like this pop up.
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