hey there everyone i currently have a thread regarding my 1993 BMW z3 in which i swapped a 350sbc small block (chevy 5.7L) V8 and Th400 transmission, the build took me about 2 months to get on the road start to finish and since then I've put over 2250 miles on it and have fixed a few minor issues and addressed a ton since the start of the project so i figure i would address challenges you may or may not run into with an engine swap (regardless of what engine you choose to swap into our chassis) specifically things you might not think about initially
Cooling, The problem i had and the solution i was battling a HUGE annoyance with cooling, not due to radiator size, fan size, or even flow it was never enough to overheat or cause real issues but i was having fluctuations on how hot or cold it would get due to air pockets getting trapped in the system, (i figured it would become a problem as my thermostat housing was significantly higher then the highest point in the radiator so that hose would get a large air pocket that was near impossible to properly bleed, I tried running no thermostat, ( helped a bit) bleeding with a comically sized funnel setup to attempt to make it the tallest part of the system (still didn't properly address the problem) i finally tried to vacuum bleed the system and that didn't seem to properly address the issue either. Fortunately i talked to an older friend of mine who is used to old school setups and he mentioned what a lot of guys do and circle track cars and in some cases even factory cars do is run an Inline radiator fill setup at the tallest part of the hose (i didn't waste the money on a chase bays one i got one from AutoZone but here is roughly what it looks like
here is a photo of a OEM setup on an infinity that uses a system like this
i basically cut open the top of the radiator hose i had been using for the setup and put the inline radiator neck filler in and hooked the overflow port up to my overflow reservoir (mine fortunately has 2 ports so I'm running one from the radiator overflow and one from this)
with this i was able to actually truly bleed the system and its been immaculate since even with me running heater lines to the stock heater core
Another issue people might run into but fortunately i was well prepared for during a swap is how to get the driveshaft setup for the BMW 4 bolt diff depending on what transmission you run you can run a normal 1310 yolk to a 1310 joint
these guys made a FANTASTIC product its genuinely the only "bolt on" style product but it fit my diff perfectly i did confirm with them it fits both small and medium case diffs with four bolts and lets you use pretty much the most common u join imaginable so any local shop worth anything can make you a solid driveshaft super simply. (here is a photo of how my driveshaft looked prior to install) mind you a 1310 can be equipped to most transmissions given there is yolks available for most transmission types and brands so this is fairly universal
One recommendation i would make however and it didn't bother or affect me but would make it easier for install ( due to how the driveshaft slides in between the diff and mounts to the diff the easiest way for me to install this was by removing the u joint, essentially separating the yoke and driveshaft, installing the driveshaft and the yolk and installing the joint while both are in the car, however if you wanted to avoid this they do make these style of slip yolks that have the bolt on clamps that you could definitely end up using.
Maintaining all of the stock electronics with a foreign engine, For context my engine is Carbureted and i made a completely separate custom harness for everything drive train related, HOWEVER you are able to keep literally all of the stock accessories for example, Radio, Power windows, AC Fan, Lights, Turn signals, pretty much you name it by literally running a single wire from any battery connection and or distribution block to the primary feed on the fuse box being this (EWSS genuinely doesn't matter or affect anything non drivetrain wise in this case) (in the picture its the red wire with the yellow connection on the left side) that's all it takes to maintain all of the stock BMW electronics with the body control module even after ripping out every single engine bay harness and all of the functioning drivetrain
these 3 possible problems and how i solved them are pretty universal to look out for regardless of engine swap so i figured id at least make a small thread on it in case someone plans on doing a swap down the line, maintaining the electronics and the driveshaft tips can be used whether its a Japanese twin turbo v6 or a German inline 5 and the cooling system portion mainly has to do with height but 2200 miles in and the cars driving great let me know if anyone has any specific or general questions with some of the stuff I've dealt with in this process (the full progress thread start to finish on my small block swap is currently on my page as well)
Cooling, The problem i had and the solution i was battling a HUGE annoyance with cooling, not due to radiator size, fan size, or even flow it was never enough to overheat or cause real issues but i was having fluctuations on how hot or cold it would get due to air pockets getting trapped in the system, (i figured it would become a problem as my thermostat housing was significantly higher then the highest point in the radiator so that hose would get a large air pocket that was near impossible to properly bleed, I tried running no thermostat, ( helped a bit) bleeding with a comically sized funnel setup to attempt to make it the tallest part of the system (still didn't properly address the problem) i finally tried to vacuum bleed the system and that didn't seem to properly address the issue either. Fortunately i talked to an older friend of mine who is used to old school setups and he mentioned what a lot of guys do and circle track cars and in some cases even factory cars do is run an Inline radiator fill setup at the tallest part of the hose (i didn't waste the money on a chase bays one i got one from AutoZone but here is roughly what it looks like
here is a photo of a OEM setup on an infinity that uses a system like this
i basically cut open the top of the radiator hose i had been using for the setup and put the inline radiator neck filler in and hooked the overflow port up to my overflow reservoir (mine fortunately has 2 ports so I'm running one from the radiator overflow and one from this)
with this i was able to actually truly bleed the system and its been immaculate since even with me running heater lines to the stock heater core
Another issue people might run into but fortunately i was well prepared for during a swap is how to get the driveshaft setup for the BMW 4 bolt diff depending on what transmission you run you can run a normal 1310 yolk to a 1310 joint
these guys made a FANTASTIC product its genuinely the only "bolt on" style product but it fit my diff perfectly i did confirm with them it fits both small and medium case diffs with four bolts and lets you use pretty much the most common u join imaginable so any local shop worth anything can make you a solid driveshaft super simply. (here is a photo of how my driveshaft looked prior to install) mind you a 1310 can be equipped to most transmissions given there is yolks available for most transmission types and brands so this is fairly universal
One recommendation i would make however and it didn't bother or affect me but would make it easier for install ( due to how the driveshaft slides in between the diff and mounts to the diff the easiest way for me to install this was by removing the u joint, essentially separating the yoke and driveshaft, installing the driveshaft and the yolk and installing the joint while both are in the car, however if you wanted to avoid this they do make these style of slip yolks that have the bolt on clamps that you could definitely end up using.
Maintaining all of the stock electronics with a foreign engine, For context my engine is Carbureted and i made a completely separate custom harness for everything drive train related, HOWEVER you are able to keep literally all of the stock accessories for example, Radio, Power windows, AC Fan, Lights, Turn signals, pretty much you name it by literally running a single wire from any battery connection and or distribution block to the primary feed on the fuse box being this (EWSS genuinely doesn't matter or affect anything non drivetrain wise in this case) (in the picture its the red wire with the yellow connection on the left side) that's all it takes to maintain all of the stock BMW electronics with the body control module even after ripping out every single engine bay harness and all of the functioning drivetrain
these 3 possible problems and how i solved them are pretty universal to look out for regardless of engine swap so i figured id at least make a small thread on it in case someone plans on doing a swap down the line, maintaining the electronics and the driveshaft tips can be used whether its a Japanese twin turbo v6 or a German inline 5 and the cooling system portion mainly has to do with height but 2200 miles in and the cars driving great let me know if anyone has any specific or general questions with some of the stuff I've dealt with in this process (the full progress thread start to finish on my small block swap is currently on my page as well)