i keep seeing stuff about block heaters pop up and i have heard that the stock block heaters caused the blocks to crack. i got an 85 6.9 i imagine the original block heater is in there the line going to it is but i never looked for the heater. anyway i am wondering why did the block heaters make the blocks crack. what would be a better replacement? and why? how much does a good one run? and any other comments on the subject

 

Never have heard any explanation of why, but I suspect it was a case of the block wall being too thin in that area and the stress of repetitive heating/cooling cycles concentrated right in one spot caused stress cracking. Just a theory though. Someone who knows the actual cause will probably chime in with it.

I have read that it was the pre-86 blocks that had the problem though. So your's probably had the heater removed or disconnected as a precautionary measure. As for other alternatives, there are several. There are 2 types of magnetic heaters that go on the oil pan that I know of. One is a round heavy duty magnet that goes in the center of the oil pan. The other is more like a heating pad with a flexible sheet magnet to hold it in place.

There are also other types too - like the ones you put into the lower heater hose, or the ones you use to replace one of your freeze plugs. Though the freeze plug type might cause the same kind of problems that the factory unit did.

 

As for the magnetic oil pan heaters do you leave those attached while driving or crawl under and remove them?

Thanks.

 

I've had one on my oil pan in my 84 for 2 years, never taken it off...if you want anything like a "block heater" go the one cheaper described.

 

ive got an 84,85 and 87 ford f250 with 6.9 diesels in em and i have never had a problem with them had to replace one cuz it quit worken but other then that no problems

 

6.9 blocks up to serial #u2u17900 had a thinner casting around the block heater. It is very common for these blocks to crack.


6.9L Old Style Block

Block Casting Number:


On left side of block (beneath oil cooler) 1805440C1
Note: Some 440 blocks are truly new style and must be visually inspected by raised donut around the block heater, frost plug (right rear). Old style below serial number 173828.
Visual Identification: *No counter bored area for block heater
*No defined area on side of block for dip stick
*Thickness of cast iron around block heater 3/8" (.375")
Head Bolts: *7/16, 12 point socket is used to torque head bolts
*Block tapped with 7/16-14 for head bolts

6.9L New Style Block

Block Casting Number: 1807996C1 Note: Some new style blocks have casting
number 440. Above serial number 173828.
Visual Identification: *Has counterbored area for block heater
*Very defined relief area cast in side of block for dip stick tube.
*Thickness of cast iron around block heater 15/32" (.470")
*Latest style (not all new style 6.9) has ribs around head bolts, rear two on left side go from head gasket surface to pan rail - same as 7.3
Head Bolts: *Same as old style 6.9

 

I was in a Ford training class back in the 90 s and the tech told us Fords explanation for the block cracking was contamination between the heater coil and block causing rerosion. That makes about as much sense as the crankshaft problem with 302 s behind the AOD tranny. Ford was just covering thier butts. My explanation for the blocks cracking is instant heat from the block heater in below freezing weather. Ford said the cranks where going out because they used the wrong flex plate bolts. The real reason was the torque converter was balloning from overheat. ( bad torque conveters )