Cracked VQ35DE heads?

[Propdr]

I'm working on a VQ35DE engine in my friends 2003 G35. What I am wondering is how common is it for this engine to develop cracks around the exhaust valve seats and or blow out head gaskets?

Engine tested positive for hydrocarbons in the cooling system and has steam coming from the exhaust when warm.

I preformed a leak down test and all cylinders were between 6-10%.The test did not produce any bubbles in the coolant withe the radiator cap off.

Any thoughts?

-Jay

[zozoka1212]

What pressure did you use? Also never heard the G with cracked headgasket here but it is possible. More possibility would be the gasket but to my remebering the leak down test need to be done in different pressures lower and higher since some leaks are only apparent when the pressure lower or hgher. 6-10% is good as far as I remember anything above 10% and more than 5% differences between cylinders are considered a problem. Am I right? Sorry these things in my memory are 20 years old.

[Propdr]

I ran the leak down test @ 80psi. As far as max % leak down 15% is where i usually start looking for major problems on a street engine. On something high performance (race) anything worse than 3% is cause for tear down. Its really subjective though, the service limit on aircraft engines is 25%.

I'm starting the tear down here in a bit and I will post pics when I run across the problem.
Modified by Propdr at 8:58 PM 1/6/2010

[tollboothwilley]

Prop DR. Do you work on Boats as well??

I haven't heard of many people having cracked heads. Not a very common issue with this motor. Not even with the 3.0L engine. Of course, anything is possible.

Go ahead and take pics of the entire tear down process for us. I'd like to see all the steps you go through.

I have heard that you should do a leak down on these engines both high and low pressure as well.

[Propdr]

Sure, I have been known to work on boats from time to time. Not really my specialty, I'm a aircraft mechanic by trade. What kind of boat do you have?

[tollboothwilley]

I hear PROP and I immediately think "boat" haha

I didnt even consider airplane propeller (although you mentioned aircraft mechanics)

Just a 23.5 ft Rinker. Family boat. Its got a 454 that needs to be tricked out. Nothing special but I love wakeboarding (even though I suck)

[Propdr]

Cool. I have fixed boat props in the past. The last one was about a 2 years ago for a friend after he bashed 1 of the 2 props on his boat really good on some rocks. Looked like new when i was done. I do all sorts of fab work and weird repairs.

[Propdr]

Progress so far....

[Tampa G35 Sedan 6MT]

The VQ is really a ugly motor.... Great but It needs a cover lmao!

DJ

[Road Ruler]

The VQ is really a ugly motor.... Great but It needs a cover lmao!

DJ

For sure, it's no looker like a 60's, 426 Hemi!