I had the usual cam thrust case oil leak that plagues most second generation Diamantes. The problem is caused by the O-ring failing. When it does, oil seeps out of the case and gets all over the engine. It a usual cause of starter failure due to oil contamination. The cam thrust case is the small cap at the rear side of the front camshaft. It is about 2 inches in diameter and is held in place with two bolts. You may think you have a rocker cover seal leak, but most likely the leak is from the cam thrust case.

Replacing the O-ring involves removing the thermostat housing to gain clearance to remove the bolts and case. That can be a real pain and involves draining the coolant, working in a cramped area, and replacing all related gaskets and O-rings. Also, since the O-ring usually begins leaking after 5 years, even if you replace it you will most likely be back to do it again in 5 years. So I thought I would first try sealing it with silicone instead of replacing the O-ring. I started with cleaning all of the oil from the area with D-Solv-It, then completely flushing and drying it. I then applied a generous bead of Permatex Gray Gasket Silicone around the perimeter of the cam thrust case and let it dry overnight. It took a few applications to get all the leaks stopped. Each time, I would remove any oil that had leaked using alcohol, since De-Solv-It would have weakened the silicone.

The final job has sealed the leak for two months now. I will monitor it and see if it works long term. Keep in mind if you go this route, and then later decide to replace the O-ring, you will be scraping a lot of silicone off.

Here is a picture of the sealed cam thrust case.

 

if you have the proper tools, you dont need to remove the coolant crossover.

but replacing the o-ring with the updated one is still the correct repair.

 

Interesting... you had told me some time ago that the coolant crossover must be removed first, saying it was "a bitch and a half" to get off as I recall. Don't the cam cover bolts hit the coolant crossover? From your previous comment, I had assumed that they do. Or are they short enough to be removed without hitting it? I haven't tried in fear of making the leak worse.

What proper tools do you need? I have a very extensive set of tools. It looks like all you would need is a GearWrench. Please explain how you remove the cover and/or replace the O-ring without removing the coolant crossover.

 

Sorry for this second question of asking, is it the rear crank oil seal that you are trying to describe that is leaking, this plate with the four bolts, is it attached to the bell housing of the gearbox ?? if so, then the oil leak, as you say, could be coming from the two half moons, of the rocker cover gasket, quick check, try and push your hand down the back of the rocker cover at the back of the engine, between the rocker cover and the bulkhead at the back of the engine and see if you can feel any oil coming out of the rocker cover, this is were the two half moons are situated, if you find that this is where the oil leak is coming from, then change the rocker cover gasket, ok best of luck.

 

CerneDef73 - From your description you are not referring to a second generation Diamante which has the 3.5L engine. There are no half moon seals in the rocker cover of the 3.5L engine. It is the rear camshaft (not crankshaft) seal I am referring to. It is a 2" diameter circular aluminum piece that is held in place with 2 bolts. It is technically called the cam thrust case but is sometimes referred to as a cam plug. It definitely is not a rocker cover leak because I had changed both rocker cover gaskets and that did not stop the leak. After applying the RTV silicone to the perimeter of the cam plug, the leak stopped.

What I am waiting on is clarification from Manybrews on how he gets the cam plug out without removing the thermostat housing which is only about 3/4" away from the top bolt of the cam plug. That doesn't appear to give enough space to remove the bolt, or even if it did, to slide the cam plug fully out to replace the O-ring. It is not a matter of reaching it with a wrench. It is easy to do with a box wrench.

In another forum Manybrews had told me that you have to remove the thermostat housing and that is why I tried the much simpler and quicker RTV sealant fix. Now he has said I could have replaced the cam plug O-ring without removing the thermostat housing. Sine I have my wife's Diamante still to fix, I have the option of replacing the O-ring, but I don't want to loosen the cam plug until I hear from Manybrews on the details of the procedure.

 

I am currently chasing down oil leaks on my engine and hope this is the answer. I just replaced the valve cover gaskets which were leaking, and, finding this thread, hope this is my answer as well, I will be diving into it tomorrow, if not tonight. Thanks to all who post fixxes here, it saves lots of cars and headaches for owners.
cheers,
Kevo

 

KevinsDiamante - You will most likely find the cam plug is the source of most, if not all, of your oil leak. My silicone fix has held up quite well for 90 days now. For my other Diamante, I am still waiting to hear back from manybrews on how to remove the cam plug and replace the O-ring without first removing the thermostat housing. He hasn't responded yet.

If you do find that the cam plug can be removed and the O-ring replaced with the thermostat housing in place, please post the procedure you followed.

 

I will go out into the garage, and, if I can do it without removing it, I will let you know, but, I have no problem with opening the cooling system. I will let you know of my findings nonetheless.
cheers,
Kevo

 

Sweet, I can log in again.....mrvivona, I successfully did the "O" ring swap without removing the water inlet. I loosened up the bolt that is too long to remove without help, then made sure I had a slightly shorter one in my junk bins. I ground off the head with a die grinder, removed the bolt, replaced the "O" ring and replaced the bolts, sweet, no leaks. Then, yesterday, I acquired another "O" ring to replace the one on the distributor and managed to replace it as well, it was another major oil leak. I have yet to drive the D and check it for leaks there. I thank the overlookers of this forum for fixxing something to allow me access once again....
cheers,
Kevo
btw, I used to post here as "Kevoz", just could never log in after initial sign up...

 

KevinsDiamante: For some reason, email notification for thread activity doesn't work consistently for me. I just found your reply. How much shorter does the replacement bolt have to be?

Manybrews: I am still interested in how you do the repair without removing the coolant parts. The same way as KevinsDiamante did it, or some other way?

For what it's worth, the silicone sealer fix I tried is still holding after four months.