I just received an 04 XJ8 from my parents in law that came with high chances of a blown head gasket. I am worried the engine block itself is warped and might just need a new engine (which i cant afford or care to pay for). Here is what they told me.

July/August 2019 - engine needs coolant every week
September - radiator blows from overheating and get replaced by mechanic
September - Engine light still on. Mechanic says its the engine block and quotes $14000 for repairs which they refuse
Ever since then until last week - they drive car just fine for 10 minutes or less without overheating or problems and add coolant every 2-3 weeks when light comes on to

As far as the codes go, for some reason when i plug in my OBDII sensor it makes the whole car go wack and throw some codes out and prevent the car from even starting. The codes that show from that experience are P0405, P1638, P1642 and P1000. In researching those none relate to a head gasket problem so i believe the OBD plug in is screwing with something. (i was planning on making a separate thread about this)

What is everyone thoughts on the situation and questions of are chances good that it could be just the head gasket? (im willing to do the work to replace it)
Are chances really high that engine block is warped and damage beyond repair?
Are there any tests i can do myself to get more precise information about the situation?

 

Post the Data Trouble Code (DTC).
Pressurize the coolant system and check for visible leaks.
Your mechanic will have the tools required

 

I dont have a mechanic that helps me out unfortunately. Thats why im trying to do it myself. As far as the codes go, for some reason when i plug in my OBDII sensor it makes the whole car go wack and throw some codes out and prevent the car from even starting. The codes that show from that experience are P0405, P1638, P1642 and P1000. In researching those none relate to a head gasket problem so i believe the OBD plug in is screwing with something.

What tool would be used to pressurize the coolant system? im pretty handy but not familiar with all the different tools out there.

 

The pressure tester is a hand pump that fits where the radiator cap goes. Perhaps one of the auto parts stores have one. The parts store may also have an OBDII reader to get the codes for you.

 

You won't really know if the block is warped until you take off the heads. However, from what I understand about these cars is they do not like to overheat.

You have a couple of tests that can be done to confirm a blown headgasket. You can pressure test the system which has been suggested. However, this can also indicate an external leak
You can buy a testing kit and some dye at your parts store. This looks like a clear bottle that you pour fluid in. You remove the cap on the coolant tank and follow the instructions. This tests for combustion gases inside the coolant. If the dye changes color you have exhaust in your coolant

For some of the more anecdotal tests:
Are the coolant hoses still firm after the car sits overnight? Exhaust gases build up pressure and that pressure remains in the cooling system after the engine has cooled down.
When you start the car up is there a bunch of white smoke from the exhaust? Coolant when burned is white, and after sitting all night, coolant makes its way into the cylinder which is burned at start up. A bad enough leak will give you a misfire at start when the car has been sitting for awhile. That excess pressure from the test above can push coolant into the cylinder and cause it.
Pull all the spark plugs. A spark plug that looks like it is steam cleaned is also a good sign of a bad gasket. There should be white or tan carbon build-up. But one that looks clean is usually a strong indicator.

For codes, the most common codes for a blown head gasket are a misfire, P0300, and low coolant. Signs are car overheats and there is coolant loss. Unless it gets real bad in which you can have a bad o2 sensor, rough idle, and maybe a catalytic inefficiency code.

Also many forums may mention the coolant mixing with oil is a bad head gasket sign. That all depends on the block and head design. My experience comes from the Cadillac Northstar engine which was designed in a way that the coolant and oil rarely mixed. In fact if they mixed, it was most likely the oil cooler built into the radiator failed. I believe from what I have seen that these cars are similar in that it is rare for the two fluids to mix.

 

The key test here is for combustion products in the coolant, as outlined by Arctic_man, but an easy test to do is to drive the car around until it's hot, then let it cool down overnight. You then remove the coolant pressure cap on the header tank with the car stone cold. If you get a "woosh" of releasing pressure, then a head gasket has almost inevitably failed, no ifs or buts

These cars were a very expensive, up-market European car, with spares prices to match. No doubt you have what looks like a really beautiful car, (I had two and loved them !), but if the engine has problems, it ain't going to be an easy fix. From your post it seems your in-laws compounded the problem by continuing to use the car even though it had a coolant problem. Not good !

Anyways, if you want to do the work,, there is a lot of stuff on the aftermarket, and used stuff on eBay, but this assumes you have the tools and know-how to fix problems, which from what I get from your post you don't have. Replacing the cylinder head gaskets is a major job, and not one I would want to do if I hadn't worked on these cars before on more minor jobs.

Sorrey if this isn't what you wanted to hear, but your problem is not an easy one to fix even DIY.

 

As I mentioned in the other thread, the AJ-V8 doesn't like to be overheated. If the diagnosis ends up being warped heads or block, it's far easier and more cost-effective to find a lower mileage engine to swap.

I assume the rest of the car is in good nick with no other issues, such as air suspension warnings?

 

Thanks for all the feedback so far. I tried to go to autozone but they closed at 630 instead of 10 due to the shelter in place here in vegas so i couldnt get them to check the codes for me yet. I'll still most likely start taking a part the engine to see if i get lucky and the engine block isnt warped. it'll also be a good learning experience for me with mechanics since i enjoy doin that stuff if its on a car i like. i dont want to (dont have the finances) spend the money on a used engine (at least $700 from what i saw not including labor). so i will be doing the work that i think is needed on the car and if it turns out to be a warped block then ill have to scrap the car.

As for now i am just trying to get a more certain "yes you should start with the head gasket" lol before i start tearing into it. i would hate to get to the head gasket and find out it was something else easier. i will update you all when i find out what the codes are for the issue.

So far there are not any other issues with the vehicle. last night i drove it to and from autozone and didnt overheat in the slightest (20 minute drive) and didnt feel any other concerns except for the "bonnet is open" warning.

 

Yes, post the DTCs when you have them.

If the heads and block are indeed warped, there is not much else that can be done except find another engine or part out the car.

 

I think you are getting ahead of yourself. Before assuming the worst get the DTCs, check the cylinder compression and do a cylinder leak down test. All aluminum blocks and heads can be destroyed by excessive temperatures, Fortunately, the manufactures installed "fail safe" controls that should turn the engine off before serious damage occurs.

 

I went to autozone to get their OBD test on the codes. It showed the same codes that i got but their tester didnt cause the car to not start or show all the warning signs on the dash. Once again those codes are

P0405 - EGR sensor - as an update with that i found the EGR electrical plug was disconnected. plugged that back in. hopefully that code goes away now.
P1638 - CAN link ECM/INSTM Circuit/Network
P1642 - CAN link Circuit
P1000 - OBD systems Readiness Test Not Complete

I dont see anything that could be connected to a blown head gasket but also doesnt explain coolant loss. Does the P1000 code have to finish doing it's thing before i can get fully accurate codes?

 

I was finally able to remove the spark plugs and got the results from my compression test.

Cylinder 1 and 4 seem quite low compared to the others. Not sure what that means right now but I'll be researching that.

 

Any plugs look like they had been cleaned? Or did they all look used?

 

I would do a leak down test on those cylinders. You have either some leaky valves, maybe some bad rings. One and four should be opposite cylinders banks.

 

Here is a picture of what they looked like although it's weird because my #5 plug had the most oil on the threads when I pulled it but did fine compression wise. I'll look at doing a leak down test next

 

I was finally able to do a Leak Down Test as well on the cylinders that failed the compression test pretty badly. Here are the results of that below

Cylinder 1 (failed compression): 40 PSI in and 10 PSI was leaking out. Heard noise from Engine Oil Cap
Cylinder 3: 28 PSI in and 2 PSI leakage. Slight Engine Oil Cap noise

Cylinder 4 (failed compression): 40 PSI in and 35 leaked out. Noise from Intake and Engine Oil Cap
Cylinder 2: 30 PSI in and 24 PSI leakage. Intake and slight Engine Oil Cap noise
Cylinder 6: 22 PSI in and 1 PSI leakage. Slight Engine Oil Cap noise

None had bubbles in the coolant reservoir and no noise from exhaust. I dont know a lot about deciphering the results but definitely looks like an intake issue mostly. Does this mean i need to take the engine down to the heads in order to repair the intake valves? In relation to replacing a head gasket, how difficult is it?

 

Sounds to me like you need a valve job. I cannot comment on the amount of work as I have never torn into a jag V-8, but I am guessing it is allot with the timing chains....

 

My take is:
1 and 2 look like they were burning oil. Heavy deposits.
None of the compression numbers look great but 1 and 4 are definitely low. As you know, if they went up when you put oil in the cylinders that usually indicates rings.
With respect to sounds, I would say if you hear air bleeding out of the Oil Filler cap that would be air entering the crankcase bypassing the rings assuming it is not bypassing through a head gasket. Since the wet numbers went up we can hope rings.
Sound from the intake would indicate air leakage through the valves.
Don't know how many miles on your engine so...if I could fix the fault code reasons I might just try to drive the car a bit and see how it plays out.
Good luck.

 

So what repair would be the easiest to start with? Im just wondering if i should just start tearing the engine down to get to the head gasket and intake valves or if theres a good chance it could be something simpler. If anyone has any thoughts.

 

Doing the work yourself,will give you the up close and personal experience of fixing your car.
Along with the confidence that is needed to take on the next issue.
Read, ask questions, study the manual take your time.
You have the luxury of not needing the car, and no money spent for the car itself.