# Rear main seal and engine replacement? **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** mustang, ford\ **Created:** [July 8, 2020, 3:16pm UTC](https://community.cartalk.com/t/rear-main-seal-and-engine-replacement/166980 "2020-07-08T15:16:21Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![J162\_165342](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/j162_165342/32/40582_2.png) [@J162\_165342](https://community.cartalk.com/u/J162_165342)\ **Post date:** [July 8, 2020, 3:16pm UTC](https://community.cartalk.com/t/rear-main-seal-and-engine-replacement/166980/1 "2020-07-08T15:16:22Z")
Hello everyone, I have a 2001 v6 mustang that I was doing an engine swap on. (Taking out the old engine and putting a new one in.) my question is, since the old engine is coming out anyway, would it be relatively easy for a mechanic to replace the rear main seal with the old engine out, before putting the new one in? Or is the rear main seal located on the engine itself and putting in the new engine would replace it anyway? Sorry for the noobie question ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [July 8, 2020, 3:19pm UTC](https://community.cartalk.com/t/rear-main-seal-and-engine-replacement/166980/2 "2020-07-08T15:19:30Z")
Yes It’s very easy to replace the seal with the engine out of the vehicle. ![image](https://global.discourse-cdn.com/cartalk/original/3X/2/c/2c17941bda0864a606e219e2434560daac748257.jpeg) Tester ---
**Author:** ![J162\_165342](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/j162_165342/32/40582_2.png) [@J162\_165342](https://community.cartalk.com/u/J162_165342)\ **Post date:** [July 8, 2020, 3:21pm UTC](https://community.cartalk.com/t/rear-main-seal-and-engine-replacement/166980/3 "2020-07-08T15:21:37Z")
So it would not be very much additional charge for the rear main seal if the engines out anyway? Do you know that if for my specific car if the transmission has to come out as well? Or could it be done with only the engine out ---
**Author:** ![Purebred](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/purebred/32/46796_2.png) [@Purebred](https://community.cartalk.com/u/Purebred)\ **Post date:** [July 8, 2020, 3:36pm UTC](https://community.cartalk.com/t/rear-main-seal-and-engine-replacement/166980/5 "2020-07-08T15:36:47Z")
What do you plan to do with the old engine? If it for the core charge, why replace the main seal? ---
**Author:** ![J162\_165342](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/j162_165342/32/40582_2.png) [@J162\_165342](https://community.cartalk.com/u/J162_165342)\ **Post date:** [July 8, 2020, 3:42pm UTC](https://community.cartalk.com/t/rear-main-seal-and-engine-replacement/166980/6 "2020-07-08T15:42:54Z")
The car has a slow leak at the moment from the rear main seal. I know this is an expensive repair so i was thinking to replace it while i have the engine already removed for the swap instead of waiting until it gets real bad and then having to pay someone again to take the engine out, so might as well do it this time when the engines already out ---
**Author:** ![J162\_165342](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/j162_165342/32/40582_2.png) [@J162\_165342](https://community.cartalk.com/u/J162_165342)\ **Post date:** [July 8, 2020, 3:43pm UTC](https://community.cartalk.com/t/rear-main-seal-and-engine-replacement/166980/7 "2020-07-08T15:43:36Z")
Or is the rear main seal on the engine itself? So are you saying if i put in the new engine i’d already be getting a new rear main seal too? ---
**Author:** ![Purebred](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/purebred/32/46796_2.png) [@Purebred](https://community.cartalk.com/u/Purebred)\ **Post date:** [July 8, 2020, 3:48pm UTC](https://community.cartalk.com/t/rear-main-seal-and-engine-replacement/166980/8 "2020-07-08T15:48:18Z")
No, I was saying if doing an engine swap, why replace the rear main seal on the old engine. Unless you are going to use the old engine in another project, why replace the seal. I would only be concerned about the replacement engine. Again, what are your plans for the old engine? What is the condition of the new engine you are installing? If it is used, sure replace the rear main in the new engine. ---
**Author:** ![J162\_165342](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/j162_165342/32/40582_2.png) [@J162\_165342](https://community.cartalk.com/u/J162_165342)\ **Post date:** [July 8, 2020, 3:50pm UTC](https://community.cartalk.com/t/rear-main-seal-and-engine-replacement/166980/9 "2020-07-08T15:50:49Z")
I thought the seal was between the engine and transmission but not on the actual engine? Or am i wrong? If it’s on the actual engine, then I would just put the new engine in and that’s it, but if it’s between the engine and trans then it would make sense to replace it when doing the swap so i wouldn’t have to pay someone later to remove the engine again to fix it ---
**Author:** ![J162\_165342](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/j162_165342/32/40582_2.png) [@J162\_165342](https://community.cartalk.com/u/J162_165342)\ **Post date:** [July 8, 2020, 3:51pm UTC](https://community.cartalk.com/t/rear-main-seal-and-engine-replacement/166980/10 "2020-07-08T15:51:28Z")
I guess my question is; is the rear main seal on the engine or is it somewhere else ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [July 8, 2020, 3:56pm UTC](https://community.cartalk.com/t/rear-main-seal-and-engine-replacement/166980/11 "2020-07-08T15:56:12Z")
The image I showed places it on the back of the engine. Tester ---
**Author:** ![Purebred](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/purebred/32/46796_2.png) [@Purebred](https://community.cartalk.com/u/Purebred)\ **Post date:** [July 8, 2020, 3:59pm UTC](https://community.cartalk.com/t/rear-main-seal-and-engine-replacement/166980/12 "2020-07-08T15:59:59Z")
In the engine block at the rear of the engine. If the donor engine is used, might as well replace the seal before it is installed. Ten minute job. If the engine is in the car the transmission has to come out . See the picture posted by Testor, that is the engine block and location of seal. ---
**Author:** ![J162\_165342](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/j162_165342/32/40582_2.png) [@J162\_165342](https://community.cartalk.com/u/J162_165342)\ **Post date:** [July 8, 2020, 4:04pm UTC](https://community.cartalk.com/t/rear-main-seal-and-engine-replacement/166980/13 "2020-07-08T16:04:41Z")
Is this the correct part: [https://shop.advanceautoparts.com/p/felpro-rear-main-bearing-seal-set-bs-40620/3216888-P](https://shop.advanceautoparts.com/p/felpro-rear-main-bearing-seal-set-bs-40620/3216888-P) Or do i need to buy some type of housing or gasket too? Or just the seal ---
**Author:** ![J162\_165342](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/j162_165342/32/40582_2.png) [@J162\_165342](https://community.cartalk.com/u/J162_165342)\ **Post date:** [July 8, 2020, 4:04pm UTC](https://community.cartalk.com/t/rear-main-seal-and-engine-replacement/166980/14 "2020-07-08T16:04:56Z")
Is this the correct part: [https://shop.advanceautoparts.com/p/felpro-rear-main-bearing-seal-set-bs-40620/3216888-P](https://shop.advanceautoparts.com/p/felpro-rear-main-bearing-seal-set-bs-40620/3216888-P) Or do i need to buy some type of housing or gasket too? Or just the seal? ---
**Author:** ![oldtimer-11](https://avatars.discourse-cdn.com/v4/letter/o/e79b87/32.png) [@oldtimer-11](https://community.cartalk.com/u/oldtimer-11)\ **Post date:** [July 8, 2020, 4:16pm UTC](https://community.cartalk.com/t/rear-main-seal-and-engine-replacement/166980/15 "2020-07-08T16:16:23Z")
If it is truly a new engine the rear mains seal is also new so there is nothing to buy. When you separate the engine and transmission . the seal is in the recess on the back of the engine. While the engine is out I would replace the front seal on the transmission because if it starts leaking you have to remove either the engine or transmission to replace it. ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [July 8, 2020, 4:33pm UTC](https://community.cartalk.com/t/rear-main-seal-and-engine-replacement/166980/16 "2020-07-08T16:33:39Z")
[![](https://global.discourse-cdn.com/cartalk/original/3X/d/e/de511eb2cf85343b6faa5ec8a4b6310d6ea2de33.jpeg "How To: Mustang Rear Main Seal Replacement (1982-2004 3.8L, 5.0L)") ](https://www.youtube.com/watch?v=RpswkE2b4k4) Tester ---
**Author:** ![It\_s-Me](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/it_s-me/32/12660_2.png) [@It\_s-Me](https://community.cartalk.com/u/It_s-Me)\ **Post date:** [July 8, 2020, 7:55pm UTC](https://community.cartalk.com/t/rear-main-seal-and-engine-replacement/166980/17 "2020-07-08T19:55:06Z")
> [@J162\_165342](#): > > I guess my question is; is the rear main seal on the engine or is it somewhere else The rear main seal is on the engine. If you are putting a new/rebuilt engine in, it will already have a new rear main seal in it. ---
**Author:** ![J162\_165342](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/j162_165342/32/40582_2.png) [@J162\_165342](https://community.cartalk.com/u/J162_165342)\ **Post date:** [July 8, 2020, 10:45pm UTC](https://community.cartalk.com/t/rear-main-seal-and-engine-replacement/166980/18 "2020-07-08T22:45:07Z")
Do you know if the radiator fan relay switch comes with the new engine as well? Or is it attached to the radiator? ---
**Author:** ![J162\_165342](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/j162_165342/32/40582_2.png) [@J162\_165342](https://community.cartalk.com/u/J162_165342)\ **Post date:** [July 8, 2020, 10:45pm UTC](https://community.cartalk.com/t/rear-main-seal-and-engine-replacement/166980/19 "2020-07-08T22:45:26Z")
Hey Tester, Do you know if the radiator fan relay switch comes with the new engine as well? Or is it attached to the radiator? ---
**Author:** ![J162\_165342](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/j162_165342/32/40582_2.png) [@J162\_165342](https://community.cartalk.com/u/J162_165342)\ **Post date:** [July 8, 2020, 10:45pm UTC](https://community.cartalk.com/t/rear-main-seal-and-engine-replacement/166980/20 "2020-07-08T22:45:46Z")
Hi, Do you know if the radiator fan relay switch comes with the new engine as well? Or is it attached to the radiator? ---
**Author:** ![J162\_165342](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/j162_165342/32/40582_2.png) [@J162\_165342](https://community.cartalk.com/u/J162_165342)\ **Post date:** [July 8, 2020, 10:46pm UTC](https://community.cartalk.com/t/rear-main-seal-and-engine-replacement/166980/21 "2020-07-08T22:46:04Z")
Hey purebred, Do you know if the radiator fan relay switch comes with the new engine as well? Or is it attached to the radiator? [Next page](https://community.cartalk.com/t/rear-main-seal-and-engine-replacement/166980.md?page=2)