Compression testing results

[Keith_J]

Took me long enough, finally found that round toit
The Lang Tool GP adapter to my Foster adapter and finally PT gauge worked perfectly. Even for #7 with the ugly oil cooler lines. Plugs looked normal despite the wide range of pressure. Lowest was #5 with 365 PSI. Highest is #8 with 420 PSI but I think it is high . Below 1 to 8 in order:

400
400
405
405
365
415
405
420

I then pulled the Schraeder valve from the Lang Tools TU-15-2A and connected it to a high pressure air source..a compressor for pre charged pneumatic air rifle..4500 PSI. Set to 500 PSI, don't need to send the cylinder head in orbit. No leak through the intake or exhaust valves but pressure in the cooling system. I keep the pressure cap lever up to prevent coolant from leaking back to the cylinders.

I ran out of time to do pressure leak down in a range of pressures. Hypothesis is the composite body of the head gasket degrades over time. This material is squeezed between the fire ring and is necessary for pressure resistance. Once the material is lost, the fire ring functions as a check valve, admitting combustion gas into the cooling jacket but preventing, at least in my case, preventing coolant under 15 PSI from causing hydraulic lock of the engine..I hope.
Won't know until the heads are pulled. Will measure piston protrusion just in case it was hydrolocked. Odds are looking like head gasket based on both compression test and 500 PSI leak down showing cooling system pressure.

 

[INFChief]

Shouldn’t the readings be 380 or higher & the lowest reading within 80% of the highest reading?

 

[Keith_J]

Shouldn’t the readings be 380 or higher & the lowest reading within 80% of the highest reading?

Exactly. I expect pressure to rise in order of testing due to oil buildup. I did driver side left bank first, then passenger side right bank.

Oil builds due to lack of glow plugs in all cylinders as lack of blow by unseats rings.

I've noticed pressurized coolant when cold for about 6 months. The low compression in #5 is completely explained by leaking head gasket. And confirmed by leakdown test showing air entering the cooling system when only #5 is pressurized.

Had #5 tested at 400 PSI without any leaking into the cooling system, 420 PSI is within the 80% mark. The engine starts, runs and drives fine otherwise. As it should for only having 36k on the odometer.