What size do you guys reccomend opening up the coolant passages in your head gaskets?

[m1garand_man]

The last time I changed my heads I opened up my head gasket coolant passages before putting in the heads. The theory was that I would get better coolant flow and prevent a cracked head. I ended up with another cracked head anyway about 15000 miles later. I didn't open them up much but I don't remember what size I made them. Should I just go in and drill .250" holes in them or .375" or leave them stock? Does it even make a difference? I'm not worried about emissions but ensuring maximum coolant flow to the heads.

 

[tim292stro]

Leave them alone. The heads are too light on the material as built and that is causing the crack (case in point the simpler smaller 5.9l Cummins weighs about 150% of what a 6.2l GM does - that's strenght by adding material). The size of the holes in the head gasket are supposed to control the flow based on the factory water flow, unless you are prepared to balance the flow with a full scale test bench or an FEA computer program, don't mess with it at all.

Question, did your replacement head crack in the same place as the last head? If so, you may have another issue you need to address.

 

[m1garand_man]

Leave them alone. The heads are too light on the material as built and that is causing the crack (case in point the simpler smaller 5.9l Cummins weighs about 150% of what a 6.2l GM does - that's strenght by adding material). The size of the holes in the head gasket are supposed to control the flow based on the factory water flow, unless you are prepared to balance the flow with a full scale test bench or an FEA computer program, don't mess with it at all.

Question, did your replacement head crack in the same place as the last head? If so, you may have another issue you need to address.

yes and no. The last head cracked in the rear most intake valve seat but it was on a completely different engine and I make the stupid mistake of advancing the fuel timing because I wasn't getting enough power when I replaced the IP with a reman.

This time the IP was timed correctly and the head cracked through two intake valve seats in the middle two cylinders.

 

[tim292stro]

Did you have the block and head decked when you installed it last time? Sounds to me like you have something wonky on the block or they weren't matched when installed last time - heads shouldn't fail after 15K miles of use (unless you're doing something wrong with them).

Small cracks can happen in the seats, as long as they don't reach into the water passage you can run the heads still - but I'd try starting with a complete new head (and valves, and springs, etc...). Make sure both the block and head are flat and true - with the cast iron as thin as it is in the 6.2/6.5 castings, any flex forced on the metal during head-bolt clamping will strain the metal.

The GM diesel is definitely a "less is more" proposition. Don't goose the power up with timing or unnecessary add-ons, let it warm up a bit before driving it a minute is not really that long to wait. The Army did a study that shows that oil when cold can take up to 45 seconds to get to all valves. Over-heating valve seats from low lube will lead to cracking...

 

[tourus]

I would start looking at other things IE radiator, water pump make sure you have good flow.. I found out the hard way.. same thing but then found no flow through the radiator so it cost me trans. and head gaskets both twice .. my own fault for rushing.

 

[m1garand_man]

Did you have the block and head decked when you installed it last time? Sounds to me like you have something wonky on the block or they weren't matched when installed last time - heads shouldn't fail after 15K miles of use (unless you're doing something wrong with them).

Small cracks can happen in the seats, as long as they don't reach into the water passage you can run the heads still - but I'd try starting with a complete new head (and valves, and springs, etc...). Make sure both the block and head are flat and true - with the cast iron as thin as it is in the 6.2/6.5 castings, any flex forced on the metal during head-bolt clamping will strain the metal.

The GM diesel is definitely a "less is more" proposition. Don't goose the power up with timing or unnecessary add-ons, let it warm up a bit before driving it a minute is not really that long to wait. The Army did a study that shows that oil when cold can take up to 45 seconds to get to all valves. Over-heating valve seats from low lube will lead to cracking...

No I did not have my block or heads decked last time nor will I have my block decked this time as it is financially impractical to have it done right now. I do find the info on letting the truck run a minute before driving off. I always wait until the after glow cycle is complete before driving away so that has probably been getting me most of the way into the time period where the oil is going where it should be. The radiator is a newer one but that doesn't mean it couldn't have plugged up in the last few years. My old heater core was plugged causing me to change it three years ago.