XC70 2000 Persistant Exhaust Manifold leaks

[lnyboer]

I'm a newbee here, but have found useful articals here in the past. Perhaps something has been written up on exhaust manifold gasket replacements that I'm not locating. My 2000 70XC with B5244T engine, has had engine light code issues (P0422) since I bought it at 80,000 miles. The frequency that it would come on increased until it was on constantly. At 129,000 miles, a Volvo service tech told me I had an exhaust manifold leak, and most likely gasket replacment would end the code problem. I dismantled and cleaned all mating surfaces without scratching or gouging anything and bought new OEM gaskets and 5 new studs and nuts of the 10 it takes. I remember wondering which direction the gaskets should face, and it seemed they only fit one way. I reassembled and tightened the nuts in two stages ending at 25nm. I completed reassembly without running the engine which I recently read was not a good choice, but had not read about running then retightening at that time. Engine codes were gone for at least 300 miles then P0422 code returned. After driving 500 miles on the new gaskets, I retightened them again. I found all the 8 inner nuts shy of 25nm and the two outer nuts still at 25nm. Reassembled and drove with light out for about 700 miles and code P0422 reappeared again. What have I not done correctly and what would you suggest I do now? Should I start all over again and get all new studs and nuts and gaskets and reinstall with a locktight agent or silicone gasket compound?

Perplexed!
Lee

[JDS60R]

Most of the time the problem with an exhaust leak is that the exhaust manifold was warped from the leak itself.

I would check the manifold for being flat or cracked.

If it is only slighly warped (most likely is if it had a leak for any length of time) I would put it on and tighten the bolts only to 12 nm and then while the engine is runing I would bring them to 25nm . This lets the manifold heat up some and it lets i bend back into place.

I the manifold is badly warped then I would replace it with an R manifold for better breathing or a salvage unit for low cost.

Volvo installatino instructions attached

[lnyboer]

So I should start all over again and replace the gaskets and bolds and nuts? This time I should tighten to 12nm cold then tighten the manifold bolts to 25nm while the engine is hot hoping to eliminate a potential warp in the manifold. Tightening from the center out.... I can do this..........

Thanks

Lee

[JDS60R]

I assume you are sure you still have a leak - can you see it or hear it??? If so

Can you take off the manifold and check it with a straight edge?

If so do it and let me know.

If flat then reistall and tighten to full torque - shoul dbe fine

If only mildy warped then replace manifold or put on with 12 and then go to 25 while running.

Must complete this in under 5 min running as bolts will heat up also and metalurgy will change . Bolts will plasticise earlier when hot . i would go 12 to put it on 18-20 when running and then turn it off right away. In about 1/2 hour come back and go to 25

[JDS60R]

Oops - new bolts are good but you already replaced 1/2 of them so no need to do again unless they are stripped.

Take a look at the old gaskets. If they are still ok then you can reuse them. I do replace them when doing this as it is cheap insurance of a good seal. If theya re stained with carbon then get new ones

[JDS60R]

Yes - new nuts/bolts - throw out the originals (when engine manufactured)and start with new. Corrosion on threads alters the torque readings. If you can chase the thread on the bolts its ok but nuts should go.

[JDS60R]

Have you read this from another board - he says unmentered intake air could be the culprit - you might want to check for intake leaks if you can't see an exhaust leak

I have been chasing a P0422 on my 2000 XC70 (140K miles) for a few months.

I may have finally resolved it in the past week.

It was an obtuse, but inexpensive problem to fix.

My approach was to eliminate all the places where un-metered air could get into the intake manifold.... clean and clamp the vacuum hoses; etc.

After checking and rechecking everything, and making some significant improvements in the performance and economy along the way, I still got an occasional P0422 under specific driving conditions.

One more check last week and I discovered that one of the two plastic clips on the intake air temperature sensor was broken off.

I bought a new one from volvo for about $20. It took 2 minutes to replace.

With only one plastic clip, the sensor will work fine at highway speed and a good vacuum in the intake. At suburban driving, the seal is not so good, and a positive pressure in the intake (like when you let you foot off the gas), might even push the sensor partially out.

IMHO, the only way that sensor got broken was when it was in the dealer for service. From the looks of the break, it has been broken for a while.

I think that this solution to P0422 would more likely apply to turbo vehicles, as the non-turbo's would not have the positive pressure in the intake.

Good luck !

[lnyboer]

I had not seen the related P0422 posting and appreciate it. The low suburb speeds were what usually set off the code originally. I'll check out all these things and thank you for your input. I was thinking I would not get a reply and all this info... Thankyou so much....

The one question I still have is, when re-installing the new exhaust manifold studs, should I torque them to 20Nm's? Is there a proseedure for reinstalling them? All of mine came out when I removed the manifold. That made it very easy to clean the head surfaces. Should I use anti-seize on the stud threads?

[JDS60R]

When reinstalling the manifold studs you should use antisieze just in case you need to take them out again someday. Use the 20NM torque value given.

An argument can be made that you can should use 18Nm to offest the lubricating properties of the antisieze. Given the materials you are using and the application you will be fine at 18or 20Nm . I would put a light coat of antisieze on ( use the brush to force it into the threads - but no globs on top. Then torque to 20Nm . Wipe any excess antisieze off before installing gaskets.

[JDS60R]

Thanks - you are more than welcome - anything I can do to help please let me know.

Ok - one more.

Here is the Volvo document concerning flanges . it specifies to use copper paste - which is basically high heat antisieze .