97 4runner still burning a little coolant after head gasket replacement... help

[alex.j.nassar]

Hi all,
I have a 97 4runner automatic with the 3.4 V6. Unfortunately it overheated twice earlier this year. The first time I just added water and forgot about it. The second time it overheated caused it to start burning coolant. I took it to my mechanic in August.After it was taken apart he told me that the block was slightly warped. He said that tolerance is +/- 3 thousandths and that my block was 4 thousandths off. I wasn't about the pay thousands more to have the block machined so I went ahead and had him complete the work.


1) New Head Gasket, Valve Cover Gasket, Intake Manifold Gasket, and Exhaust Manifold Gasket.
2) Machined both heads
3) New Head Bolts
4) New timing belt
5) New water pump
6) New Thermostat
7) Adjusted all valves



Ever since I got it back it runs great and gets better gas mileage than it did before. When I start it cold it blows some normal steam and then once warmed up it runs perfectly with no sign of coolant in the exhaust. For some reason I have noticed at times that when I start the motor when it is already hot it will blow a little coolant out the tailpipe. There is no coolant in the oil and I only notice any sign of this problem when the motor is started while there is pressure in the radiator. For example, I start the engine in the morning with no coolant in the exhaust (radiator not under pressure). I get on the freeway and drive 15 miles and park at work. Come back 10 minutes later and start the motor and it blows coolant out the tailpipe for a minute or so. Whereas, if I get to work and park it for 2 hours and then start it there is no coolant in the exhaust (again no pressure). I have experimented with letting the pressure out of the radiator after I park. I have noticed that if I do that it does not blow coolant ever. I have started doing this every time I stop the motor with the intention of restarting it right away but needless to say, that is annoying. What could be the problem? What would cause it to blow coolant only when the radiator is under pressure? Help please…

Thanks in advance!

 

[02SE]

Well, without knowing the quality or accuracy of your Mechanics work, I'd say the warped block might likely be your problem.

If that's the case, the fix is to take it apart, and have the block decked.

 

[alex.j.nassar]

What I want to know is how a castiron block would have warped in the first place. It seems like whatever warpage there is would have been from the factory. I mean, it takes over 2000 degrees to melt castiron while the aluminum heads melt at like 1200 degrees. How could the block have gotten hot enough to warp? Also, why does it only blow coolant sometimes but not always?

 

[02SE]

Measurable Block or head deformation or warping can occur at lower temperatures than the melting point of the material.

Was your block that way from the factory? I don't know. Toyota is pretty good about tolerances, so I feel pretty confident it was within manufacturer tolerances when it was first assembled.

Needing to remove a little material isn't uncommon to get them within tolerance.

4 thousandths is more than I would call acceptable. And could be the cause of the problem you're having.

Another question is whether the necessary RA of the surfaces was followed for the type of headgasket used. There is no mention of that, so we have no idea.

Just based solely on the information your Mechanic gave you, and you gave us, I'd say the problem is likely the block being out of tolerance.

Good luck.

 

[brian2sun]

I agree with everything 02SE said.

Overheating is so bad for the engine. Wherever the coolant is seeping through is probably small enough that it seals up with the temp changes in the engine. My old engine had 2 cracked heads for over a year and ran fine most of the time, until it just got worse and worse to the point it missed like crazy. But coolant out of your tailpipe means the head gasket is leaking (probably from a warped block in your case) or there's a crack in the head or block that was missed when it was all apart. Hopefully it's not the latter. I'm wondering why it was gonna be thousands more to resurface the block? AFAIK, that's usually a few hundred bucks??

 

[nissanh]

When the engine is running the pressure in the piston/cylinder is so great that it will push air into your radiator (according to your description, you have compression and coolant line connection). Do you see your reserve tank is getting full after a trip?

Try this when the engine is COLD!

Remove the radiator cap.
Start the engine.
Put your palm to cover the radiator opening
Now, open the reserve tank, while keeping the end of the rubber hose in the reserve tank immersed in the coolant, look for any bubbles coming out.

If you see bubbles coming out continuously, bad head gasket. You can rev the engine and see what happens.
No bubbles = good head gasket (no connection between the cylinder and coolant)

Finally, how do you know that is coolant coming out from the exhaust?

 

[shadow247]

Lisle 75500 Combustion Leak Detector : Amazon.com : Automotive

Get a block tester. It's a surefire way to know if you have combustion gasses entering the cooling system. Is it using coolant? If not then I'd say you have another issue.

 

[02SE]

Also, why does it only blow coolant sometimes but not always?

Okay, the cast iron block, and the Aluminum heads expand and contract at different rates. This isn't a problem, as long as the tolerances for a flat block deck are in spec, and the same for tolerances for the flatness of the cylinder heads themselves. They can expand and contract and the headgasket(s) will still maintain the seal between the block and head(s).

If the tolerances are out of spec, as your Mechanic apparently advised that the engine block was, the headgasket(s) is much more likely to not be able to maintain the seal as the block and head(s) expand and contract at different rates. That is most likely what is happening here.

4 thousandths is too much of a variance in deck flatness (IMO) over the relatively short length of the 5VZ-FE V6 block. I wouldn't accept that amount of variance in a block deck, even in a long I-6 engine.

Of course cracks in the heads or block are also a possibility. But if he was accomplished enough to check the block and heads for flatness, I would hope he would have been thorough enough to check for cracks, too.

I'm really surprised that any Mechanic would proceed with re-assembly, knowing it was out of spec. Maybe he was hoping to be lucky and it would outlast any warranty period he might have on his repairs.

At this point I'd take it back and see what he has to say.

 

[iowajosh]

That is what worries you? Cause I was worried that one little spec of crap could get under the gasket and keep it from sealing. Or The block surface was too pitted. My bargain manual actually said to torque 90 degrees but didn't mention the other 90 degrees that the head needs to be torqued down. There are a lot of things that could go wrong.

 

[02SE]

That is what worries you? Cause I was worried that one little spec of crap could get under the gasket and keep it from sealing. Or The block surface was too pitted. My bargain manual actually said to torque 90 degrees but didn't mention the other 90 degrees that the head needs to be torqued down. There are a lot of things that could go wrong.

I don't know if you're referring to me, but I'll reply in case you are.

I'm not worried at all. Although I do feel bad for the OP.

Yes, lots of mistakes can be made, and lots of things can go wrong. However, anybody that calls themselves a Mechanic, and charges for their services, should have the expertise to ensure that things don't go wrong very often. When the rare occasion happens and something does go wrong, they should have a policy to fix those errors.

As someone that has built lots of engines over the years, I'll just say that you need to have the basics covered, if you want the engine to be long-lived, and reliable.

Something as basic as starting out with all the parts within acceptable tolerances, is absolutely necessary to achieving that goal.

We know that the Mechanic stated the block was out of acceptable tolerances, when it came to the deck of the block. You simply can't expect to have an engine that doesn't have headgasket sealing problems, if you start out with an unacceptably uneven deck surface.

Why this Mechanic would agree to assemble an engine that was known to have an out of tolerance block deck, is beyond me.

 

[Diagram14]

OP, have you had to top off you coolant reserve since the HG job? If you mentioned it I missed it. I know after I did my HG I was paranoid about it not holding and every hint of steam out of the exhaust had me micromanaging my coolant levels for peace of mind.

 

[nissanh]

Before we make any more comments, we have to wait until "Alex, J N" says something.

 

[alex.j.nassar]

Op back

Its been a while but I am back.

Shortly after that first post I replaced the radiator cap. Apparently my mechanic didn't replace that and I didn't think of it. The old pressure release radiator cap wasn't working properly and too much pressure was being created. I replaced the cap in January and I haven't blown any coolant since. The old girl has over 200k now and runs as good as she did when she was new.

 

[alex.j.nassar]

 

[BrianSD_42]

Great outcome!

 

[Kung]

Now that's good news.

 

[02SE]

Its been a while but I am back.

Shortly after that first post I replaced the radiator cap. Apparently my mechanic didn't replace that and I didn't think of it. The old pressure release radiator cap wasn't working properly and too much pressure was being created. I replaced the cap in January and I haven't blown any coolant since. The old girl has over 200k now and runs as good as she did when she was new.

I'm glad to hear that's working out for now. You should be aware that if a faulty radiator cap was causing enough excess pressure in the cooling system, to cause a headgasket leak, and replacing the cap stopped the headgasket leak, then the seal created by the headgasket is tenuous.

The plastic caps on the top and bottom of the radiator, or the rubber hoses would give up, before a properly sealing headgasket.

I hope it holds up for years, but keep an eye on it.