1989 e34 m20b25 into an 1986 eta

[e30.4.life]

I just received a donor 1989 525i with a recently rebuilt m20b25.

I have a 1986 325es. The eta motor has over 255k and it burns and leaks lots of oil and is in desperate need of being rebuilt.

I want to take the m20b25 out of the 1989 525i and swap it into the 1986 325es.

Has anyone ever done a swap like this? (e34 i motor to an eta)


I would really appreciate any feedback.

One of my main concerns is finding the appropriate wire harness. From what I have read I think I should try to find a 1987 325i wire harness to mate the 89 m20b25 to the 86 325es. Is this correct?

I figure once I have the m20b25 out of the 525i then it's just like any other m20b25, and if I want to do an eta to i swap, I should find a m20b25 wire harness from an e30 that is as close to the recipient car's model year as possible. In my case, with a 1986 e30 eta, I should look for a wire harness from a 1987 325i or is. What do you think? Am I on the right path?

What am I missing or over looking?

Lastly, what else should I scavenge or use off of the 1989 e34 for the e30?

Also, if anyone wants parts off the car, let me know. The donor car is going to the yard as soon as the motor is out of it. Pay for shipping and the parts are yours.

We will be pulling the motor the weekend after Christmas.

Any and all thoughts/opinions are welcome. Thanks!

[mikegar]

you need to make an adapter for the i harness to connect to the body. on the i it has a round plug and on your car you have a square plug.

you are correct with the wiring harness, and you should replace your gauge cluster as well.
and i would also get a 173 ecu

[SpecM]

you can use any e30 325i wiring harness, '87-91

[e30.4.life]

What is the best way to make the plug?

Should I just cut the square end of my old eta harness and splice it to the i harness?

Is there somewhere I can get the correct plug, so that I don't have to cut up both wire harnesses?

Also, the coolant systems are different. Am I forced into finding an 87 or later radiator and coolant hoses?

I know that the coolant hose configuration is different between the two motors.
The coolant hose configuration on my 86 sucks. (Fan cut one of my coolant hoses once and made a huge mess. No surprise for us eta owners. )

Do I have other options for the coolant system? I just bought a brand new radiator less than 6 months ago for the eta and it wasn't free if you know what I mean.

I think might be able to scavenge the brake booster from the 525i. What about the steering rack?

Any thoughts on what parts I should take off the 89 525i before I send it to it's grave?

Thanks a lot for your input! :)