Triumph Repair: 75 TR6 Black Wet Exhaust, head gasket leak, coolant leaks

Question
QUESTION: Howard,

You've been a great help in the past so hopefully you can help again!

'75 TR6, rebuilt head with new valves/guides, trued, and leak checked in spring 2010.  Carb rebuilds at same time.  All this was required as the #4 intake vale was leaking.  Now have good compression on all 6, timing and mixture all predictable, performance has been very much improved: steady throb and good "oomph". Water pump new in 2007.  New hoses all around in 2010 including heater hoses.  New thermostat, new heater valve.  Cleaned EGR, new water return pipe to water pump housing.  Water pump itself was replaced in 2006.

However, shortly after the head rebuild, I had the lower rad hose pop off while driving after a highway run.  Fortunately I heard it and was beside a service station so the fix was inconveinent but nothing more.  I blamed a poor access making for a poorly tighented hose clamp on my part.  However, the top rad hose (new in 2010) is weeping through it's woven core (indicating to me high temp/pressure).

The car itself runs very hot in city traffic.  Highway is fine.  10 minutes of stop and go in 25C summer weather means I'm watching the temp gauge nervously.

I have had only one "white puff" of exhaust smoke after the rebuild.  There are no burning oil or coolant clouds behind me.  There are no coolant leaks under car.  My oil is changed every 3000 kms and I've had 3 changes since the head rebuild and everything was normal.  I have no oil foaming in the valve cover so I am sure I have no internal leaks.  But....

My coolant bottle always needs to be topped up and my twin exhausts spit a moist carbon mist. You can't see it but put your hand in from of it and it comes away well speckled.  The proof of it being there all the time is that the back of the car is always quite filthy.  It dries to a non-oily state.

Here's my logic: Coolant is going somewhere.  But where?

1)  I can't have a head gasket leak between cylinders as you'd see that on a compression check (comps are very good)
2)  I can't have a head gasket leak between a coolant channel and a cylinder as you'd see that as a burned coolant cloud coming from the exhaust (again, only ever had a small puff right after the reassembly and nothing since then)
3)  Rad itself shows no leak.  Have not tried to use an IR temperature sensor to map temperature across surface to see if there is an blockages/gunked up areas.
5)  Coolant is getting into the exhaust manifold in an unburned state and bringing with it all kinds of carbon scrubbed through the resonator and mufflers.
6)  My water pump is not functioning meaning the engine coolant is not being circulated effectively.  This means overtemps and weeping of fluid (doesn't explain the exhaust angle though).

Any suggestions?  I really want to avoid pulling the head if it isn't required but everything I think point to a leak between between a cooling channel and the exhaust flange?

Thoughts?

Nelson
75 TR6



My

ANSWER: Hi Nelson,

You have done a lot but you are making a couple of diagnosis on misconceptions.

#1. Is not correct. only a really badly blown head gasket shows up on a compression test.
#2. Is also not correct. only a badly blown gasket will blow white smoke out the tail pipe.

There are three good tests of a mild head gasket (or crack somewhere)leak.
1. Is to have the open radiator sniffed with CO/HC equipment. (some shops don't like to do that because of filters in the equipment get contaminated.
2. Put the radiator dye in the coolant and watch for color change due to CO in the coolant (the dye is available at most auto parts stores)
3. A 100% effective test is to get the adapter that fits in place of a spark plug and put that piston on TDC and brake on hard and put air line pressure 125 to 150 PSI in the combustion chamber and watch the open radiator for signs of the coolant raising. This test will show the smallest leak that may not even show up as a over heating or a long term coolant loss.

#2 test is an effective test and not expensive nor time consuming. If the dye turns color as per the instructions on the container it then would be wise to get the adapter (most mechanic's tool trucks carry the adapter and they are not expensive) and run the #3 test on every cylinder to pin-point the problem.

Running hot is city traffic is a common fault in all the old British sports cars. MG, Triumph and Jaguar. An accessory electric fan added in front of the radiator as a blow through fan tends to correct the problem. I usually put a dash mounted manual switch as below 35 MPH is when it is needed and in stop and go traffic.

Howard

---------- FOLLOW-UP ----------

QUESTION: Thanks Howard.

I pulled the head yesterday and found nothing out of place.  No cracks seen, no signs of leaks.  The only thing I saw was lots of carbon.  All six exhaust ports were dry and unremarkable.

The engine block looked good.  There was some carbon in the recesses/lips of the cylinders.  That was cleaned out before reinstallation.

Exhaust gasket showed some leakage areas and I had one stud in the area that was marginal.  Again, all reinstalled after cleaning and inspection.

Everything ran again after I reinstalled the cooling system and the induction/carbs.  A little timing adjustment and it was ticking over as before.  Water pump seemed to be moving fluid through the system (could feel it in the hoses).  One hose seemed a little collapsed so I may change that one just to be sure.

So ...... didn't solve anything but did at least reset the diagnostic clock.

I have a spark plug fitting for my compressor so I think I'm going to go directly to test #3.  I'll let you know how it turns out.

I have an electric fan kit in my garage at the bottom of the "things to do" so I guess that moves to near the top.

Thanks
Nelson

ANSWER: Nelson, You confuse me. Why did you remove the head without FIRST doing the tests?

Also, what do you mean by "No cracks seen" The best auto machine shops can't "See" cracks with their eyes most of the time and have to use a process called "Magnaflux" on iron heads. So how can you see cracks?

Also, it sounds to me like you accidently found your problem and bypassed it. You said you found carbon in the recess on the lip of the cylinders.

There can not be any carbon in that recess unless you used the wrong head gasket or installed it up-side-down. That recess is called a "Flycut" and is the highest pressure point of the head gasket. (only on late model TR-6) The correct gasket has an extra thick ring made on the gasket to fit into that flycut recess. If you use an early gasket there is NO high pressure applied around each combustion chamber. Thus asking for leakage now or in a few miles down the road.

First check the part number of the head gasket to see that it does NOT fit early TR-6 and ONLY fits late TR-6. Both look alike other then that thick ring around each cylinder. If the part number claims to fit all TR-6 you need to find a correct supplier and get the correct gasket.

Howard

Another point. You said "one hose looked a little collapsed". If that was a lower hose(return hose) you should replace it before running the engine again.

---------- FOLLOW-UP ----------

QUESTION: Sorry to create confusion Howard. Guilty as charged for putting the cart before the horse. I fell victim to the "I have the parts and the time" syndrome!

The head gasket I removed did have the right cylinder lip configuration with the metal sealing rings for the flycuts.  However, the gasket was aftermarket and very, very thin compared to the one I purchased from Moss (using my engine/car production number).  Both had the tang on the aft edge denoting it for the later model TR6 blocks.  Given the carbon build up in the #5 cylinder recess, I suspect that was the source of the problem and, as you say, I may have already solved the problem.  I'll run the pressure test after I retorque the head bolts to spec.

As to cracks, I was looking for macro stuff.  The head shop checked the head for leaks when I had the new valves installed and it checked out clean.  My only concern was whether the over-temp I had may have done damage.  I did a good cleaning around mating surfaces and did a visual with 10x magnifier.  I also have an eddy current tester that I did some playing around with but it's tough as to interpretation.  Bottom line is that I didn't find anything that looked like a crack or a result thereof.

New lower hose is already on order......

I'll let you know should the sooty exhaust not resolve itself.

Thanks

Nelson

Answer
It does sound like the gasket was at fault but the #3 test is a very good test for even the smallest leak and is good for even the smallest valve leakage by just opening the throttle and listen in the carbs with a hose in the ear and the same at the tail pipe. even the slightest leak in the valves can also be spotted.

Ring blow by can only be done by performing the test of many cars because even the best sealing rings will hiss in the crankcase which can be heard by opening the oil filler cap. Only by testing many cars could we tell what was a acceptable hiss or unacceptable hiss.

For ring test we used the dry & wet compression tests which was accurate. Not as good as a leak down tester but good enough.

Let me know how it turns out.

Howard