2004 Grand Marquis LS Rear Differential Fluid, ATF...

[Russian]

Re: 2004 Grand Marquis LS Rear Differential Fluid, ATF...

Recently bought the above referenced car at just under 69,000 miles. Manual says 80w90 for rear diff fluid. Numerous sources say it's okay to use a synthetic 75w 90, taking about two and a half quarts.

I'm near certain my car doesn't require an additive. Does anyone know for sure? My mechanic will be able to tell for sure when the car is up on a lift. A number of the full synthetic 75w 90 fluids say they've the limited slip differential additive already in it. Is harm done using such a fluid on a car not requiring it?

Any suggestions on which 75w 90 brand to use and those to stay away from? Is Lucas a good option?

Is the Fel-Pro RDS 55341 gasket cover a good option? Two different Ford parts departments told me there's no OEM for this part and said to use RTV, which I sense isn't as good as the Fel-Pro option with a good quick dry sealant. Please advise.

The ATF on the car had a dark Robitussin color upon purchase. Ever two weeks with the car warm, I'd suck out about a quart and a half of ATF, replacing it with the Ford approved Mercon V put out by Walmart Supertech. I did this eight times. Is it a good idea at some point within the next ten thousand miles to do a drop pan ATF and filter change as well?

My other planned maintenance issues will be the spark plugs (going with stock Mororcraft), gas filter (looks like it was already changed and will be changed again with the OEM part). I replaced upper and lower hoses and did a braking system bleed. I've done the power steering fluid via the turkey baster method. Serpentime belt to be changed as well.

For the engine oil, I'm using Walmart full synthetic with a Motorcraft filter, every four months/about 4,000 miles.

 

[BAJA_05]

Whats the deal with Russian for a screen name????

 

[GSCJR]

harm done using such a fluid on a car not requiring it?

No.

Is the Fel-Pro RDS 55341 gasket cover a good option?

Yes or RTV is fine too.

Is it a good idea at some point within the next ten thousand miles to do a drop pan ATF and filter change as well?

Yes.

 

[bdcardinal]

Ford did not use a gasket on the differential cover on these, they used RTV. Lube Locker is the best gasket on the market for diff covers. RTV is fine as long as you let it set up before adding fluid. Pro-tip: remove the fill plug on the front of the diff before taking off the cover. You don't want the not be able to refill the diff.

If your vehicle has a Track-Lok (limited slip) it will require an additive unless the fluid you choose already has it mixed in. If you shoot me a PM with your VIN I can tell you for sure but IIRC only the HPP equipped Whales had a limited slip.

Absolutely drop the pan and change the fluid and filter. If there is a little plastic floaty bobber thing in there that means either it has never been done before or someone left it in there. That is the dipstick plug from the assembly line. The factory trans pan gasket is reusable but the replacement number is F2VY-7A191-A if you need one.

 

[Lubener]

^^Great advice on loosening the diffie's fill plug prior to draining.

I did those fluid changes and services on my 2003 Grand Marquis a few years ago. I used Mobil 1- 75w-90 in the differential which I already had.. I used a Fel Pro gasket, no RTV for me. Took about 2.25-2.5 quarts. The transmission was pan dropped. The original pan gasket is reusable, I used Castrol Mercon V fluid (S-Tech is fine), a Motorcraft trransmission filter and a new ATP oil pan with a drain plug. That pan added about an extra quart as it is deeper than the original. Took about 6.5 quarts. The converter has no drain plug after 2002. I used a Motorcraft fuel filter. I haven't done plugs as the car only has 45k miles. I already have OEM motorcraft plugs and new boots when the time comes at 60k miles.

The 4.6 2v engine is famous for blowing spark plugs out of the heads. I suggest that you do NOT use anti seize on the new plugs and find the torque specs for the new plugs. It's very critical to do it right or you will have problems down the road with the plugs loosening, damaging the few threads in the head and eventually blowing the plug out of the head.

 

[Russian]

Ford did not use a gasket on the differential cover on these, they used RTV. Lube Locker is the best gasket on the market for diff covers. RTV is fine as long as you let it set up before adding fluid. Pro-tip: remove the fill plug on the front of the diff before taking off the cover. You don't want the not be able to refill the diff.

If your vehicle has a Track-Lok (limited slip) it will require an additive unless the fluid you choose already has it mixed in. If you shoot me a PM with your VIN I can tell you for sure but IIRC only the HPP equipped Whales had a limited slip.

Absolutely drop the pan and change the fluid and filter. If there is a little plastic floaty bobber thing in there that means either it has never been done before or someone left it in there. That is the dipstick plug from the assembly line. The factory trans pan gasket is reusable but the replacement number is F2VY-7A191-A if you need one.

Thanks. The last eight digits of the VIN is 4X695999.

On the RTV, I prefer not to wait for it to cure.

 

[Russian]

I did those fluid changes and services on my 2003 Grand Marquis a few years ago. I used Mobil 1- 75w-90 in the differential which I already had.. I used a Fel Pro gasket, no RTV for me. Took about 2.25-2.5 quarts. The transmission was pan dropped. The original pan gasket is reusable, I used Castrol Mercon V fluid (S-Tech is fine), a Motorcraft trransmission filter and a new ATP oil pan with a drain plug. That pan added about an extra quart as it is deeper than the original. Took about 6.5 quarts. The converter has no drain plug after 2002. I used a Motorcraft fuel filter. I haven't done plugs as the car only has 45k miles. I already have OEM motorcraft plugs and new boots when the time comes at 60k miles.

Thanks. Did you use any kind of epoxy/epoxy like product when applying the rear diff gasket cover?

 

[bdcardinal]

Thanks. The last eight digits of the VIN is 4X695999.

You have an open safety recall, 15S39 for inoperative headlights. You can take it to the dealer and they will do the fix for you, might have to order parts since it is a 9 year old recall.

 

[Lubener]

Thanks. Did you use any kind of epoxy/epoxy like product when applying the rear diff gasket cover?

I applied the gasket dry.

 

[Lubener]

You have an open safety recall, 15S39 for inoperative headlights. You can take it to the dealer and they will do the fix for you, might have to order parts since it is a 9 year old recall.

Had that done already. They replaced the lighting control module (LCM).

 

[barkingspider]

Felpro gaskets have always worked for me so recommend using it over RTV. Just use a little bit of locktite on the bolts for the cover so they don’t come loose. You will be fine using 75w90 w LS already in it. If it was mine, I would use 80w90

 

[Russian]

You have an open safety recall, 15S39 for inoperative headlights. You can take it to the dealer and they will do the fix for you, might have to order parts since it is a 9 year old recall.

Thanks. Are you able to tell if it needs the rear diff fluid additive? I'll ck to see if the prior owner answered the aforementioned safety recall. At some point I'll replace the existing lenses and go to LED.

 

[bdcardinal]

Thanks. Are you able to tell if it needs the rear diff fluid additive? I'll ck to see if the prior owner answered the aforementioned safety recall. At some point I'll replace the existing lenses and go to LED.

Open diff, no modifier needed.

 

[Russian]

Felpro gaskets have always worked for me so recommend using it over RTV. Just use a little bit of locktite on the bolts for the cover so they don’t come loose. You will be fine using 75w90 w LS already in it. If it was mine, I would use 80w90

STP makes a conventional 80w 90 without and modifier for LSD. The Walmart Supertech 80w 90 is a conventional with the added modifier.

At issue is what's better 75w 90 full synthetic or 80w 90 conventional?

 

[Rob_Roy]

If you live in a cold climate the 75w-90 would be worthwhile, otherwise just stick with 80w-90.

 

[Russian]

^^Great advice on loosening the diffie's fill plug prior to draining.

I did those fluid changes and services on my 2003 Grand Marquis a few years ago. I used Mobil 1- 75w-90 in the differential which I already had.. I used a Fel Pro gasket, no RTV for me. Took about 2.25-2.5 quarts. The transmission was pan dropped. The original pan gasket is reusable, I used Castrol Mercon V fluid (S-Tech is fine), a Motorcraft trransmission filter and a new ATP oil pan with a drain plug. That pan added about an extra quart as it is deeper than the original. Took about 6.5 quarts. The converter has no drain plug after 2002. I used a Motorcraft fuel filter. I haven't done plugs as the car only has 45k miles. I already have OEM motorcraft plugs and new boots when the time comes at 60k miles.

The 4.6 2v engine is famous for blowing spark plugs out of the heads. I suggest that you do NOT use anti seize on the new plugs and find the torque specs for the new plugs. It's very critical to do it right or you will have problems down the road with the plugs loosening, damaging the few threads in the head and eventually blowing the plug out of the head.

No.

Yes or RTV is fine too.

If you live in a cold climate the 75w-90 would be worthwhile, otherwise just stick with 80w-90.

Thanks. With the NY metro area in mind, what's an acceptable price for having this work done (rear diff fluid and gasket change on an 04 Grand Marquis)? I've gotten ranges in the $100-$125 range (one shop) to $200 (from another). Both shops with excellent reputations.

 

[GSCJR]

Estimates look correct, I would have estimated $200.

 

[RF Overlord]

@Russian: Using a gear lube with LS additive will not cause any harm to your open diff.

Felpro gaskets have always worked for me so recommend using it over RTV.

I like Fel-Pro gaskets on the diff cover as well.

At issue is what's better 75w 90 full synthetic or 80w 90 conventional?

Ford specs 75W-140 synthetic for this same axle when used in the Police Interceptor or the F150

Also, yes definitely do a transmission pan drop. Check the pan for clutch wear debris and the magnet for metallic sludge. (Some is normal). Use a Motorcraft FT-105 filter. Pro tip- either install a drain plug or use a replacement pan with drain plug built in. Makes future fluid changes WAY less messy.