1970 455 coolant loss / compression test pls advice

Just recently I noticed the exhaust seal at cyl#8 bubbling a little and the whitish color at the exhaust manifold in that area pointed me towards coolant residue.

So I started investigating.
- coolant level in radiator is getting lower. Not fast, but since I check regularly it apparently gets worse.
- no signs of oil in coolant.
- engine oil is not milky.
- trans oil is not milky.
- no visible outside coolant leaks. Radiator is a new Champion AE161.
- spark plugs look okay to me. On the pics they appear more black/oily than in reality.

Did a compression check on warm (not hot) engine and the results are:

cyl...psi
1...197
3...207
5...197
7...207

2...197
4...203
6...200
8...203

Since owning the car I thought the engine is pretty much stock, but those values are way higher than expected. Too high even? Cyl #8 does not stand out, the numbers are quite close to each other.

Until the compression check my scenario was to replace intake and cylinder head gaskets, which would cure the issue of coolant loss - so my thinking, as I was not able to find any other suspect causes.

Now, with the measured compression values I really wonder if those are okay for a street driven car, as in: do I need to do something to bring those down?

Engine by itself runs fine. At wide open throttle (which I usually do avoid) there is some noticeable knocking going on, otherwise no signs of knocking.

The 'SS' block stamping is still visible so it seems to have not been machined so far. Other than that, no idea about the engine build.

Any advice on how to proceed?

 

I doubt you have an issue. The bubbles you see is an external leak boiling on the hot exhaust. You simply would not see coolant burning through the exhaust manifold gasket. Also the manifold looks perfectly normal to me.. again a white discoloration on the exterior of the manifold would not indicate an internal leak. Clean oil, clean plugs and no running issues tell me you do not have a head gasket failure.

My free advice- don't sweat it. Keep track of how much coolant your using and go from there. Diagnose a possible coolant leak before you fire the parts cannon. You may have a loose clamp or something simple like that.

 

Loss of coolant may not even be engine related. It could be the heater core. Check for wet carpet on passenger side floor board.

 

I would check both heater hoses and connections since they are right above the area you are concerned about

 

okay, I checked heater hoses, floor board and all the clamp locations of the other hoses - everything is as dry as the Mojave desert.
The exhaust seal #8 is definitively leaky, I can see and hear it when the engine runs. I could tighten the bolts a little more and it became better.
--> My conclusion still is that the coolant gets lost somewhere inside the engine.

Any comments on the compression values? 200 psi translate into around 13.8 bar, which means I have a dynamic compression ratio at cranking speed in the area of 14:1?! This is not sound, is it?

 

I'd try another compression tester and see if you get the same readings. That is high, but I dont know if you can equate it to compression or DCR.

 

Yes, a non calibrated or false reading compression gauge was my first thought, so I already cross-checked the compression test gauge with a second pressure gauge and it seems to read correct.

 

How much are you losing?

 

Hard to tell exactly, filled it up as before as good as possible. 1 quart in 30 miles is the ballpark. I keep watching it.

 

A quart in 30 miles would be evident in the oil or on the plugs. Thats a huge amount of coolant. I would verify the loss and try to keep track of it. Have you checked the weep hole in the water pump?

 

My coolant level is like 2 inches from the radiator cap.. If I top it up, it will be lower after each time I drive the car, until it reaches the same level again.. I have no overheating etc issues..

 

@Joe, I hear you, makes sense to me.
Will do some driving and crosscheck everything again, the pump as well.

 

can you pressure test the cooling system? that would rule out any peripheral leaks

 

Not at present, but I could buy a pressure test kit for 40 Euros... but then, why would it rule out only peripheral leaks? My understanding is, it is kind of a black and white test, either the system holds pressure or not. If not, the root cause could be anywhere in the entire cooling system. Let's e.g. assume the intake gasket is not longer sealing properly at the coolant channel in the back and there is a small drip of coolant into intake #8 passage, the pressure test would turn out negative as well, or? Am I missing something here?

 

Okay, got that. I can say that when I turn off the hot engine, with a then pressurized cooling system, the pressure does not immediately drop. The upper radiator hose stays pumped up for quite a while (this is subjective of course but nevertheless). I am not able to detect any kind of water puddle anywhere around the engine and under the car.
I know, that goes against the quite high amount of coolant loss... well, as said before let me double-check everything after some additional miles. Will report again.

As it really troubles me - are the 200 psi / 13.8 bar compression values something I need to adress? Ignition timing is set as recommended in Larry's thread. Engine has some WOT detonation going on, otherwise it seems fine.

 

Thanks Larry, that's something I need to digest...

 

Any chance the engine has Rhoads lifters in it? In my experience, those lifters can produce some very high cylinder pressure numbers. An engine I had with the TA 290-H cam and 10.2:1 compression produced 200 PSI pressures like you're seeing. My current engine with a TA 413 roller and 10.6:1 compression produces numbers in the 160-180 range.

If you don't have Rhoads lifters, advanced cam timing can have the same effect. If your camshaft was not degreed when installed or was intentionally installed with significant advance, it could account for the high cylinder pressure you are measuring.

 

First Guess: You don't have an overflow tank, and you're OVERFILLING THE RADIATOR.

If there's no overflow tank, the radiator should be stamped with a "fill level" that's at least two inches down from the cap. Overfill the radiator, the excess blows out the overflow hose onto the ground, you never see an external leak because it on the road, not on the engine.

If you DO have an overflow tank, do you have the correct radiator cap? The cap for an overflow tank-equipped vehicle has an extra rubber seal that prevents the radiator from sucking air as the engine cools.