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I recently had an oil leak from the back of my intake manifold. I’ve got a 78 with a 351m and an Edelbrock performer 400 intake. So I changed the valley pan, used RTV as recommended instead of the rubber gaskets, put it all together and had a coolant leak from the back of the intake. I took the intake back off and saw some coolant pooled under the valley pan as well. I think I may have messed up when torquing the bolts and over-torqued the very first one. I followed the pattern on the Edelbrock instructions. My questions is, could over torquing the first bolt cause this issue with the coolant leaking internally and externally or should I be looking at something else?
 

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Did you put the bolts in and just torque them one by one or did you snug them and couple of times then final torque?
 

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I tightened them by hand, then torqued em one by one starting at 25 ft lbs, going over every bolt a few times. But I’ve been told I should’ve started at a quarter of that and work my way up little by little.
 

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The 351M/400 and 351C ALL have dry manifolds, so coolant can't get out there. My bet is a blown head gasket or a cracked block. What numbers are on the block? Ford had some bad molds that lead to certain year blocks to crack, usually between the lifters and the head surface. This was a problem with bad molds, NOT a problem with the engines engineering.

"Foundry casting codes and date codes are significant for M-block engine blocks because some blocks that were cast before March 2, 1977 at the Michigan Casting Center are prone to water jacket cracking in the lifter valley area. Blocks cast at the Michigan Casting Center after that date do not have the cracking problem.."
 

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'95 XLT: 5.8, MAF, E4OD, 4.56's, 6" lift on 33's
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What he said... ^^^^^^^^^^^^^^

I just picked up a used 400 block for that very reason. My ol' lady has one of the M casting blocks and I can't verify the block number because of a poor stamp, so I picked up a different C block to avoid rebuilding a potentially bad block. Hope your issue is simpler but it's a known issue that I'd never head of until recently.
 

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Discussion Starter #7
The 351M/400 and 351C ALL have dry manifolds, so coolant can't get out there. My bet is a blown head gasket or a cracked block. What numbers are on the block? Ford had some bad molds that lead to certain year blocks to crack, usually between the lifters and the head surface. This was a problem with bad molds, NOT a problem with the engines engineering.

"Foundry casting codes and date codes are significant for M-block engine blocks because some blocks that were cast before March 2, 1977 at the Michigan Casting Center are prone to water jacket cracking in the lifter valley area. Blocks cast at the Michigan Casting Center after that date do not have the cracking problem.."
on the back of the block next to the oil sending unit it says 8D12. I’m hoping that 8 in for 1978?
 
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