Leak down test - possible BHG

toyota
coolant
supra
leaks
gaskets

#1

I just did a leak down test on my 86.5 Toyota Supra turbo, I was looking to find the basic health of the engine. I don’t have an actual leak down tester so I ran compressed air set at 90psi straight into each cylinder set at tdc. For every cylinder, the coolant in my radiator started rising and spilling over, no bubbles were present. Does this mean I have a blown head gasket or something worse? I was told by the previous owner that the engine has a metal hg with arp studs that were torqued to 80 ft-lbs.

Thanks


#2

Did you just buy this vehicle or what?

There’s definitely a problem there but the cause could be anything. A severely warped cylinder head, wrong head gasket, mismatched cylinder head/block combination, etc.

A metal head gasket (copper?) and studs along with a Turbocharger and on a Supra kind of points to someone wanting to whale on it quite hard.

Spark plug tips wet with coolant or have a bleached appearance?


#3

The turbo is stock, the metal head gasket was used because supras are notorious for blowing head gaskets. I’v had the car for a couple of years now and it runs great but I can’t seem to keep air out of the cooling system. The spark plugs have a white powder on the tips.


#4

What sympton is the air in the cooling system causing (I know what it typicaly causes, but I want you to say it) You are making some rather startling observations but linking these observations to a “everything is great” statement. Sooner or later you are going to have to say what your car is doing that concerns you


#5

Every morning I start the car I hear the waterfall noise behind the dash, when I burp the system it goes away only temporarily. There is also whitish/grey smoke out of the exhaust when it starts, I know its not valve seals because I just replaced them and before I did the car used to emit A LOT more smoke on startup. I don’t mean to be vague but these are the only symptoms. The car does run good which puzzles me, I did a compression test and got these results: cylinders 1-6 170,170,182,175,180,180. They seem good which is weird because every cylinder leaks into the coolant chambers according to the test I did.
edit: The car has only ever overheated on my once and that was about 2 years ago.


#6

What is your “burp” method? have you ever just drove and not “burped” the car, does anything happen that you would care to report if you do not “burp” your car every morning?


#7

The compression is fairly decent for an aged vehicle and it would be extremely, extremely rare for a head gasket breach to exist on every cylinder.
The whitish powder can certainly be a sign of burning coolant.

It’s been a bunch of years since I’ve messed around with one of these cars and I simply don’t remember but is engine coolant routed through the intake manifold in any place?
If there is and if there is a breach in the gasket in that particular spot then that could provide a common location for any air being applied to any cylinder to surface and cause a problem like this.


#8

The only possible passage for air pressure to get from the cylinder(s) to the coolant with the valves closed is via the headgasket. That would indicate to me a breech caused by either a warped head, a blown headgasket, or perhaps even an improper prior headgasket installation. Pressure passing from every cylinder to the water jacket would suggest to me an improper installation. Perhaps the surfaces were not properly cleaned, perhaps flatness wasn’t properly checked, perhaps the proper torque pattern wasn’t followed, or perhaps even there were unaddressed erosion paths from the previous headgasket breech. Perhaps even the wrong gasket was somehow used, or the installation orientation was incorrect. It does happen.

Bottom line: every symptom you have suggests an improper prior headgasket installation.


#9

Looks like I’ll be pulling the head this weekend, what you are saying makes perfect sense. Hopefully the problem is just an improper installation, I wonder if I will have to have the block resurfaced as well?


#10

I didn’t mean to say that I burped the car every day, but when the water sound behind the dash gets worse (every couple of months or so), I jack up the front of the car a couple of feet, turn on the car with the heater blowing hot and watch the bubbles come out through the radiator inlet, refilling as necessary.


#11

The only way to tell is a good cleaning, a good inspection, and a good flatness check.

When you put the new headgasket in, let me suggest that rather than use the orientation of the current one you double check the proper orientation. As strange as it seems, people have been known to put gaskets in upside down or backwards and that can cause problems. With some gaskets I’ve seen this is possible.

Best of luck with this.


#12

Thank you, I will post my findings when I have them.


#13

I finished pulling the head yesterday, here’s what I found. As far as I can tell the head gasket looked ok. Cylinders 3, 5 and 6 had excessive oil and carbon build up on the pistons and valves. I knew my car smoked a little at startup, I had replaced the valve stem seals last summer so I?m guessing the valve guides are worn. Since the engine has good compression (as posted above) can I safely rule out bad rings? I checked the head and block for warping and found the block to be ok but the head is slightly warped. The head also seems to have been surfaced by a hand sander/grinder, not by a machine shop which along with the warping would explain the leak down test making the coolant rise. I?m will be taking the head to a machine shop in a couple of days. Attached is a picture of the valves for cylinders 5 and 6 and the head gasket.


#14

You cannot rule out rings, compression readings good or not. It’s quite possible to have great compression readings and a severe oil burner at the same time. This is why I always say that a compression or leakdown test is not 100% definitive.
Based on the grunge on those valves I’d say there’s a ring problem.

(An actual xample of my above statement. A 4 cylinder engine with 185 PSI on all 4 cylinders. This engine used oil at the rate of 1 quart per 10 miles and it was due to only 1 of the 4 cylinders although the compression was the same on all 4.)


#15

Now that I have the whole engine apart is there any way to confirm bad rings short of taking the block out of the car and sending it to a machine shop?


#16

I should also note that when my car was running that it only smoked a bit on startup and I never noticed any smoke while driving, also I never had to add any oil in between oil changes.


#17

At this point, and considering the compression readings, I would not go into the engine lower end. That often leads to one of those “what next” scenarios. The time to check for a ring problem would be before the head was removed and during a wet compression test.

Those valves look awful grungy but if oil consumption is at a minimum it may be best to live with it.

The only thing I can think of in regards to the compressed air/bubbling coolant thing is that the cylinder head is badly (horribly even) misshapen. It’s extremely rare that one would be bad enough to cause this on all cylinders but it’s possible I suppose.


#18

Let me ask this. You say the head gasket is metal. Does this mean 100% metal or is it fiber with metal inserts? The pic is a bit unclear to me due to the grunge on the gasket.

If it’s all metal I would advise you to replace it with a stock gasket along with a few tweaks.
Spray the new gasket with aerosol Copper Coat. This can help greatly in sealing a new head gasket.
Allow the head nuts to sit idle for a few hours after torquing them and then retorque them again.
After about 500 miles of use go back and recheck the torque on the cylinder head nuts and tighten as necessary.

Hope that helps.


#19

I copied your image and zoomed it, and noticed what looks like a clear breech to the water jacket on the bottom of the left cylinder of the shot with the valves in it. I tried unsuccessfully to post the enlarged image, but click on the “download” and you’ll be able to expand it and see what I mean.

Realize that

  1. the pressures blowing combustion gasses into the water jacket are substantial, and the combustion pressure can exceed 2,000 degrees.
  2. the suction during the intake stroke that can draw coolant into the cylinder can be substantial, and the coolant is kept at roughly 15-16 psi.

Or am I seeing too much into the photo?


#20

OK4450, do me a favor. Enlarge the photo of the underside of the head and look at the bottom of the left cylinder. Tell me if you agree that there appears to be an erosion path there. It could have been created before the headgasket replacement by the previous owner and would allow passage without having to have breakage in the new headgasket (the one in the photo).