3.5 liter Mk. IV Engine issues

Well my day in the garage with filled with many ups and one big down today. Finally got my 3.5 liter MK iV running again today after a two year restoration. Had to fit many small leaks all today but finally got running smoothly by late afternoon. While tuning we continued to notice small amount of coolant along the head gasket on both sides of the motor near the front cylinder. On closer inspection we notice small bubbles along a hair line crack centered on the front right head stud dome nut. Also noticed similar on the left side between the freeze plug and head mating surface.

SO NOW WHAT? Are there any spares out there or should I look into having if professional inspected and welded. Any thoughts? concerns? helpful hints?

Thanks in advance, Jim Bolinger (Canton, Ohio, USA)

Greetings All,

You might want to look into metal stitching, especially if you want to save the block.

Not sure if fire-ringing the combustion chambers would help depends on where the leak is coming and going.

Would be interested if any fluid is getting into the combustion chamber?

Otherwise your problem is the fluid is just leaving the block, that could be manageable.

Blocks were a bit prone to cracking between the end stud and the corner of the block The ones I’ve seen were at the rear RHS . Later head castings had a bit more metal at that point.
heads [ and blocks ] can be pressure tested . Or even a simple crack test for a start.
As Bob said the Metaloc process would be the best repair…
Or is it the gasket not sealing

Were the head and block faced?
What sort of gasket?
How accurate is the tension wrench calibration?
Were the studs taken out of the block and the threads o them and in the block checked for corrosion ?
Did any f the head gasket crush protrude into the combustion chamber?

I haven’t pulled the spark plugs to see if any I an see if coolant is burning in the cylinders. No stean noticed from the exhaust. So at this point if it is leaking in combustion chamber is unknown.

I never had engine apart except for removing head to replace a head gasket about a year ago. Has not run since then. Now thinking this was unneccesary as leaks might have been coming from crack.

When I had apart I left studs in block up cleaned everything from there up. I used a new gasket from Worchester Spares but not sure of manufacture. I did not surfcae block or head but checked both with a stout metal straightedge.

I’ll go back to garage today and hopefully gather more info.

Thanks to all - Jim

Front spark plug may be a little lighter in color than others but this may be because of distance from carb also. So I’d say not conclusive of coolant getting in cylinder bore. There was steam coming from the exhaust along with a watery liquid. Color was clear and there was no sweet smell of anti-freeze so again no direct evidence on way or the other.

So I guess my game plan is to pull the head, take it to shop and have them clean it up and magnaflux to see what I have. During that time frame I’ll educate myself on metal stitching versus welding.

Water vapor is a prominent component of normal gas engine exhaust. When engine is relatively cold we see the condensation trail and condensed drops coming out the cold tail pipe. When engine and tail pipe are hot the steam of normal exhaust product is no longer visible. Looking for excess water or antifreeze evidence out the tail pipe is a comparison process for normal/abnormal levels and components for the running conditions. On starting up an engine after fresh work, adrenaline can make one worry too quickly about water in the tail pipe.

Was the head properly torqued with a calibrated torque wrench?

Are the head nuts and washers correct? There are acorn/dome nuts out there which do not have sufficient internal thread clearance. These nuts will seat on the head bolt and may not pull down on the head properly.

What is the path of the fluid and bubbles you see, exit source from head, block, joining surfaces and the internal sources which could lead there? There are multiple possible paths, more or less annoying and troubling.

Could you describe the cracks in more detail, location and extent?

Did the coolant level in the radiator diminish after steady running temperature was achieved?

There are several forensics questions which might well be worth pursuing before pulling the head (with associated time, head bolt stress, and expense). Once the head is pulled, the running conditions and symptoms cannot be retested.

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And is there cottage cheese in the oil? Is there creamy color in oil, visible in oil through rocker cover oil fill lid hole, or visible on oil coating inside of rocker cover? All these are evidence of water getting into the oil. You may already know this, I’m just trying to be thorough in early suggestions for this worrisome moment.


Many of the items you mention are common items that I know but it never hurts to have anotherr set of eyes when diagnosis problems! So don’t worry how elementary the questions/comments are.

Let me go into a little more detail on the engine condition. Before starting on a cosmetic and some mechanical issues restoration 2 years ago the car was running and had completed about 200 miles in my hands. At that time the only issues I observed related to the engine where weeping of coolant along the block/head gasket on the front cylinder. From the looks of the staining on the block it appears to have been leaking for a while. The was not much loss of coolant of any white deposits in oil or valve cover area.

During my repairs i removed the head, cleaned both surfaces, cleaned out stud holes with fine sandpaper, cleaned exposed studs, checked both surfaces with thick metal straightedge to be if warped and reassembled with new (more expense) gasket from Worchester Spares.

The only item replaced except the head gasket was the chrome acorn nuts. Washers appeared to be correct and original. When I reassembled it was at a professional auto repair shop that has been in business for years and even worked at MG, Jag dealer in area for years in the late 50’s and 60’s. He maintains his tools regularly so assume torque wrench is close to accurate. WHen we torques head we did not notice and bottoming of threads in dome nuts before it the head appeared to be tight but this is always a possibility.

As far as crack location and visible signs. Ther is no coolant leaking when car is not running. After starting and allowing it to idle for 5-10 minutes. I notice small bubbles of coolant forming along a crack which runs the the 2nd dome nuted head stud on the right side of the engine back at a 45 degree angle towards the m front exhaust port stud on the middle exhaust runner on the front exhaust manifold. There also appears to be a similiar crack rinning from the other side of this head stud forward on the top of the head towards the raised diamond shaped letter in the head casting. This fluid puddle will continue to grow over time and then run down the head to the head gasket seam. My guess on volume is maybe 1-2 teaspoons in 10-15 minutes of running.

On the left side of the block it is harder to identify exactly where the fluid is coming from due to external water jacket, carbs, etc. I do see 2-3 areas the appears the water is runnig down the side of the block to the head gasket seam. The worst of these (by volume) appears to go from the 8 o’clock position in the front freeze plug downways at a 45 angle to the head/block mating surface. I cannot define the exact crack path like the top of the head since gravity is working on the fluid before it forms large bubbles. I have not identified exactly where the other streams are coming from but have felt the bottom mating surfaces of the external water jacket ports and do not feel this is the source. The head gasket seam on the left side is wet almost the full length of the block. In the same 10-15 minute running time I guess there was 2-3 tablespoons of fluid loss on this side.

To tell you the truth I did not look at the fluid level in radiator after running the car nor look for any white substance in oil or valve cover area. Unfortunately I work about 3 hours away for the car during the week so won’t be back until Friday to check this.

The only other thought we had is to retorque the head bolts but I won’t think less than a half hour of total run time after installation would cause this much loosening.

As always and thoughts, questions or comments would be appreciated.

The last two Jaguar engines I rebuilt had what we calll “fire-rings”.

These were XK units, but the procedure is the same.

Going to try to upload a picture.

Fire-ringing is where a groove is cut into the cylinder liner. A ring is fitted before the gasket is installed. The ring is seated into the groove that was machined into the liner. The groove depth is 1/2 the diameter of the ring. This leaves the other half of the ring to exert pressure on the gasket.

This procedure typically used with Diesel engines to deal with the excessive compression ratios used by diesels.<img src="//jl-discourse-uploads.s3.amazonaws.com/original/2X/5/5000d23ada4b22b42aa506f06cacdedfb1f749ce.JPG" width="666" height="500">

I could see how this would contain cylinder compression getting into the cooling system but how would it help with coolant leaks from cracks?

Ok Issues that one can stirke with 3 1/2 engines

The blocks [ or the deck of the block] an pulll up around the stud holes. Often caused by previous use of a copper / asbestos head gasket. If one removes the studs and runs a mill file across the deck , you can see it shiny around the stud holes. Fix is to face the deck off , or a tleast draw file with a good new mill file.
The stud holes go into water jackets so the studs or female threads can corrode, Fix id Recoil kits in corroded holes [ ideally done in a mill to get them perfectly square/ and or new studs]
The acorn nuts can bottom out when tightening usually because facing the block / and or deck brings the top of the head closer to the deck , fix is to check ech studs protrusion from the top of the head and campare against the dome nut.
The centre row of studs go through the inlet tract , which by now is full of carbon , Unless this id cleaned out pieces of carbon can fall onto the head gasket when dropping the head back on .
Depending on what size bores standard sized head gaskets may not fit the bores properly… Of tenwhen reconditioners are reboring, they will have moved the bores slightly towards the worn side andprogressively this can affect the gasket fit
The head gasket you got was made here in Melbourne They are also made to suit over sized bores.
The head should be tensioned and the engine started and warmed up , Then the rocker gear removed and the head retensioned. . I know , annoying to have to fell like a step backwards . But then a further retension after about 500 miles. There is a correct method to re tensioning.
be cause hthe 3 1/2 lost one row of studs, it is more likely to weep on the LHS.
When fitting the head , apart from brain surgery cleanliness a thin coat of Hyplomar should be sprayed on the gasket { THIN]
The heads should be tensioned using a deep socket to get an accurate reading . Something not easy to find ina Whit size and you may findthe places is making do with a standard socket . But using standard depth sockets usually damages the dome nut and c an lead to inaccurate reading.

here endeth the sermon .

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Greetings All,

It doesn’t.

Question for Ed…what is it about the copper/asbestos gaskets that lead to failure…lack of compressibility that overstresses the threads of the fasteners?


The copper / asbestos gaskets are too thick allowing the studs to pull up the deck of the block
Jaguar went to shim gaskets instead of copper asbestos very early in the SS jaguar engine manufacture.
The factory gaskets then were Payen, a shim with a pressed ridge around all the holes. Unfortunately not a method tat lends itself to small volume production. So now they are made of a thin modern composite material with steel crushes.
Pulling up of the deck had been an issue with jaguar for along time . In the end theXJ 6 engines had the studs go right to the bottom of the crankcase. Which may have worked if BmC hadn’t changed the spec of the steel used…
The reasoning being that as long as the corosion inhibitor was maitained as specified it would be all right … fat hope of that being done by owners.

Greetings All,

I’m seeing aluminum shim show up on occasion instead of copper, any worries with those?

They look the same otherwise.

Here are some thoughts on soft head gaskets and block pulling, not tested or confirmed.

From the top, the head side, the head bolt pulls down on the nut which in turn pushes the head down. The downward force of that one nut acts over a wide area at the gasket from the head side and acts from a large distance away from the gasket, that distance being roughly the thickness of the head.

From the block, the head bolt is pulled upwards by the nut at the top of the head.The forces of the bolt on the block occur at the bolt threads. These threads begin at the block deck and go a ways into the block. These thread forces on the block pull upwards on the block starting right at the top of the thread and running to the end of thread engagement with localization near the block deck and vertically, not spread out much and not far from the block deck.

If an absolutely incompressible gasket were to be used, the torque action on tightening the head bolt nut would stretch the head bolt as normal but no pull upwards of the block deck would occur because there would be no space into which the block could elastically be pulled upwards. An elastic or plastic response of the block is prevented.

If a compressible gasket is used, at every stage of progressive tightening of the head bolt nut, the block material will have a localized elastic or plastic movement upwards until the block either encounters material which prevents further pulling upwards of the block or the torque setting is reached. If the elastic limit of the block material is reached then the deck will not be flat when examined later, it will show evidence of the “pull”.

All materials have some compressibility, so one issue in gasket design is to decide how much compressibility is acceptable for the application.

Greetings All,

This is partially true, but please tell me then, how do the threads fail?

Thread failure is complicated to describe and my understanding is quite limited. Bolt threads act partly in shear (which provides the tension along the shank) with the shear stress acting over a radial extent of the thread. By shear I mean pushing the thread over in a direction nearly along the bolt axis, not along the thread peak path. Bolt threads also act partly in torsion. The combination of the torsion and shear seems pretty complicated to me, I tend to think of the shear stress only and estimate the torsion adds some factor to that force. The shear stress also can expand the thread diameter of the outer piece (block or nut) replying to the shear force. This expansion of the outer threaded piece may reduce the area over which the shear stress acts, increasing the chance of going past the elastic limits of the bolt threads. Also, when threads are “chased” in rebuilds, the geometry will no longer have original design specifications for the contact areas between the bolt threads and the block, again making it easier for bolt threads to fail when bringing the torque up towards required number. Also, bolts may be damaged in multiple usages if the elastic limits are exceeded. Bolt designs tend to have torque specifications running from 75-90% of the elastic limit, an out-of-calibration torque wrench is not a good friend.

A small factor also, is the the threads for the head studs do not come right to the surface but start about one turn below the deck
Or did when the engine was new

I have seen recoils put in with the thread right up to yje sirface , and worse. protruding .


I’ve never seen an alloy one I suppose they would work as long as the alloy was till annealed and not work hardened from rattling rou din someones ute for a couple of years.