This is why you should listen to your mechanic

[The_Eric]

Long story short, I've got a customer who has an 85 Mercury Marquis 3.8 V6. It blew both head gaskets and got HOT! So hot that it temporarily seized. He wanted my opinion- I told him to replace it. He didn't want to spend the money, but yet the car does have sentimental value... Got it all back together (heads checked out okay) and it wasn't running like I wanted- rough and down on power. Pulled out the lab scope to do a relative compression test- it's hurtin for certain.

Now the guy is left with a good sized repair bill and a wounded engine. I really feel for him, but I warned him that bad things could result.

If you look at the picture, the two vertical lines mark one complete revolution. #1 to #1. Note the 3 low peaks of the yellow/brown graph. They equal low compression. The green graph is just the number one cylinder for reference.

 

[raytseng]

Can you clarify what you recommended the client to replace versus what he decided to do?

You said don't bother repairing the engine replace the whole thing? and he said let's try to patch it up first instead?

What was the price quotes on each option?

 

[Ducked]

The mechanics I've listened to here don't sound like this.

Not even my inner mechanic, which is the one I mostly have to listen to.

How does the oscilloscope sense compression?

I vaguely recall something about sensing resistance across the plugs but that might have been for pre-ignition.

 

[Merkava_4]

I always thought a Mercury Grand Marquis would have a 4.6L V8.

 

[Chris142]

He got it so hot that he killed the rings

 

[bdcardinal]

Originally Posted By: Merkava_4
I always thought a Mercury Grand Marquis would have a 4.6L V8.


An 85 Marquis, not Grand Marquis, could have had a V6.

 

[Ifixyawata]

Originally Posted By: Merkava_4
I always thought a Mercury Grand Marquis would have a 4.6L V8.


Probably an old 80s Fox chassis Marquis. I used to have an old 84 Ford LTD, Fox chassis with the same v6. Most were 3.8 some had straight 6 and some models 5.0 but those are quite rare. See LTD LX...

 

[Rand]

in 1985 there was no 4.6 It transitioned in early 90's

for example the thunderbird was 5.0 in 93 and 4.6 in 94

and also its not a grand marquis.

 

[bdcardinal]

Originally Posted By: Rand
in 1985 there was no 4.6 It transitioned in early 90's

for example the thunderbird was 5.0 in 93 and 4.6 in 94

and also its not a grand marquis.


1992 was the first year for a 4.6 in a Grand Marquis, I had one. The first use of the 4.6 was in the 1991 Town Car.

 

[Trav]

If there are no broken rings try a 50/50mix of kerosene and Gumout carb cleaner soak for a couple of days. 100% a Hail Mary pass but worth a shot IMO.

 

[eljefino]

OP is talking about this thing:

Surprised it's even still around.

 

[The_Eric]

Originally Posted By: raytseng
Can you clarify what you recommended the client to replace versus what he decided to do?

You said don't bother repairing the engine replace the whole thing? and he said let's try to patch it up first instead?

What was the price quotes on each option?


You've got it correct. I wanted to sell him a long block. He elected to to try just putting head gaskets in it.
(understandably didn't want to spend the coin) He did bring up an alternative line of long blocks, but I recommended to avoid them, even though they were about a grand less.




Originally Posted By: Ducked
The mechanics I've listened to here don't sound like this.

Not even my inner mechanic, which is the one I mostly have to listen to.

How does the oscilloscope sense compression?

I vaguely recall something about sensing resistance across the plugs but that might have been for pre-ignition.


What do you mean about mechs not sounding like this?

I used the scope and an amp clamp to sense the amperage draw of the starter. The current draw goes up with each successive compression event. Cylinders with less compression will show on the graph as lower amperage readings. As I said before, the lower trace is a probe that is clamped to the #1 plug wire. The scope sees the spark on that cylinder and records it. I use it for reference, so if you know #1 and the firing order, you can identify which cylinders are low. In this case #1, #2 and #5, if I recall.


I posted this mainly to show the other end of the interaction and what your mech might have already dealt with- to possibly give some insight on his/her thinking or way(s) that they deal with things.

 

[The_Eric]

Originally Posted By: eljefino
OP is talking about this thing:

Surprised it's even still around.


Yep, that's it! The car in question is in the same shape too, despite being a rust belt car.

 

[Lubener]

Originally Posted By: Merkava_4
I always thought a Mercury Grand Marquis would have a 4.6L V8.


The 4.6 wasn't even a twinkle in an engineer's eyes back in 85. Would have been a 5.0L.as an option. There was a smaller vehicle back in 85 called a Marquis and then there was a bigger vehicle which was named Gran Marquis. A 3.3L inline six was discontinued in 83.

 

[Kruse]

Originally Posted By: The_Eric
He wanted my opinion- I told him to replace it.


As someone who has WAY too much experience with the 3.8 motor (my kid actually has one in a '96 T-bird as I type), you would have my admiration if you told him to replace the entire GD car...with some other car that does NOT have the 3.8 motor.

 

[CKN]

Must be a BITOG forum member who thinks the Panther platforms are the greatest cars in the world.....

 

[bullwinkle]

Originally Posted By: The_Eric
Originally Posted By: raytseng
Can you clarify what you recommended the client to replace versus what he decided to do?

You said don't bother repairing the engine replace the whole thing? and he said let's try to patch it up first instead?

What was the price quotes on each option?


You've got it correct. I wanted to sell him a long block. He elected to to try just putting head gaskets in it.
(understandably didn't want to spend the coin) He did bring up an alternative line of long blocks, but I recommended to avoid them, even though they were about a grand less.




Originally Posted By: Ducked
The mechanics I've listened to here don't sound like this.

Not even my inner mechanic, which is the one I mostly have to listen to.

How does the oscilloscope sense compression?

I vaguely recall something about sensing resistance across the plugs but that might have been for pre-ignition.


What do you mean about mechs not sounding like this?

I used the scope and an amp clamp to sense the amperage draw of the starter. The current draw goes up with each successive compression event. Cylinders with less compression will show on the graph as lower amperage readings. As I said before, the lower trace is a probe that is clamped to the #1 plug wire. The scope sees the spark on that cylinder and records it. I use it for reference, so if you know #1 and the firing order, you can identify which cylinders are low. In this case #1, #2 and #5, if I recall.


I posted this mainly to show the other end of the interaction and what your mech might have already dealt with- to possibly give some insight on his/her thinking or way(s) that they deal with things.
That's an interesting way to test for compression, that would be a lot faster than the old fashioned way of pulling all the plugs & using a compression tester. Has the idea of a junkyard motor came up? Especially if you could find one with a good bottom end & reuse those rebuilt heads.

 

[The_Eric]

Originally Posted By: Lubener
Originally Posted By: Merkava_4
I always thought a Mercury Grand Marquis would have a 4.6L V8.


The 4.6 wasn't even a twinkle in an engineer's eyes back in 85. Would have been a 5.0L.as an option. There was a smaller vehicle back in 85 called a Marquis and then there was a bigger vehicle which was named Gran Marquis. A 3.3L inline six was discontinued in 83.


I think the 5.0 was only available to our brothers to the north?




Originally Posted By: Kruse
Originally Posted By: The_Eric
He wanted my opinion- I told him to replace it.


As someone who has WAY too much experience with the 3.8 motor (my kid actually has one in a '96 T-bird as I type), you would have my admiration if you told him to replace the entire GD car...with some other car that does NOT have the 3.8 motor.



LOL!!! Talked to the guy today and it sounds like it was quite problematic- especially with oil leaks, when his dad owned it.... Poor guy!

 

[slacktide_bitog]

It's a Fox body, so lots of potential

 

[Ethan1]

Originally Posted By: CKN
Must be a BITOG forum member who thinks the Panther platforms are the greatest cars in the world.....


The car in question is a Fox, not a Panther. They are both awesome