Compression Test Question

[TheBocSez]

I decided to do a compression test on my 91 LX. Here is what I did so tell me what I did wrong and if my numbers look ok.

Engine warm (Temp gauge reading 180*)
Removed all spark plugs
Disconnected Coil wire
Intalled compression gauge
cranked engine for about 10sec per cylineder
checked gauge.

I did not prop the throttle blade open, I did not disconnect the fuel pump in anyway. I understand these are mistakes so do you think they affected my numbers?

#1 138 psi (8th checked)
#2 135 psi (7th checked)
#3 140 psi (6th checked)
#4 140 psi (5th checked)
#5 150 psi (1st checked)
#6 145 psi (2nd checked)
#7 145 psi (3rd checked)
#8 145 psi (4th checked)

I know the rule of thumb is "less than 10% varience is ok" but why the difference between #8 and #1? Only factor I can think of that I checked each cyl in this order 5-6-7-8-4-3-2-1.

Would cooling of the engine from time and maybe the fuel being squirted into the cyl have an affect?

My combo is this.

302
Probe pistions p/n 10682 valve relief volume 4.0 cc
(compression Ratios 58cc=9.35 / 61cc=9.02 / 64cc=8.72 / 68cc=8.35)

Probe rings 1/16 1/16 3/16

Custom Cam (213/221 @.050 520/519 lift 114 lsa) installed straight up.

E7 Powerheads

Felpro 1011-1 (.041 thickness) head gaskets

Not sure what other info is needed or would affect compression. I also dont know what CC the powerhead are so I really have no Idea what compression I am running.

So, what are your thoughts? Ok?

 

[HISSIN50]

Personally I think it's fine. I cant offer much that you dont already know. A wet test afterwards would have revealed a little about ring seal, but I dont think it was necessary.

A battery charger can help keep things even as well.

I think it's fine (there are so many variances in testing, absolute numbers are kinda useless - just the relative spread and yours is pretty decent).

Good luck.

 

[Cman88]

Personally, I don't like to rely on compression test results to show the condition of an engine. Its a good general tool to help show with how the chamber is sealing, but won't really show smaller/medium issues.... only larger leaks. In my case, I showed 140 on every cylinder. Nice and even. The test didn't show me the blown headgasket on #6. A leak down test would be more usefull for trying to pinpoint problems, if that was your goal. Just my opinion.

 

[TheBocSez]

Yeah, it actually was. I am suffering from a little blown head gasket paranoia. I had an overheating issue a short time ago and it did heat up pretty good once. I replaced my thermostat, radiator, and cap (the pump was new)and the overheating has gone away as far as I can tell. The only issue I have is that the overflow fills up. It dosent overflow and I dont see any bubbles, no fluids mixing. Like I said, just me being paranoid.

I know its a little off the topic of my thread but which is the most accurate way to determine a headgasket failure?

Coolant system pressure test
Cylinder Leak down test
Block Test kit ( the one where the fluid changes colors)

 

[Cman88]

I wound up purchasing a block testing kit and going that route. I do a lot of sidework for people so I figured I would more then make my money back on the cost of the kit.

My car was constantly running around 3/4 of the way up the gauge. Previous owner had a Ford "master technician" diagnose the car and he ruled out the head gaskets. I was constantly loosing coolant with no signs of leaks. Thermostat was boiled and shown to open correctly, water pump was correctly circulating coolant as it should. Even with pure water in the system (previous owner did this as well), the car was running on the "Warm" side. The block tester kit didn't turn completely yellow like it should, but the fluid went from a dark blue to a greenish color. Upon removal of the cylinder heads I found the #6 cylinder was the problem along with quite a few other things along the way. The problem with a very small headgasket leak is it may not even show up in the leakdown test. Its possible to leak in a fashion that it creates a one way check valve sort of effect. I would say from my experience that the block test is about as 100% as you can get. A combination of all three tests would be, of course, the best route if you are in doubt.

 

[TheBocSez]

I wound up purchasing a block testing kit and going that route. I do a lot of sidework for people so I figured I would more then make my money back on the cost of the kit.

My car was constantly running around 3/4 of the way up the gauge. Previous owner had a Ford "master technician" diagnose the car and he ruled out the head gaskets. I was constantly loosing coolant with no signs of leaks. Thermostat was boiled and shown to open correctly, water pump was correctly circulating coolant as it should. Even with pure water in the system (previous owner did this as well), the car was running on the "Warm" side. The block tester kit didn't turn completely yellow like it should, but the fluid went from a dark blue to a greenish color. Upon removal of the cylinder heads I found the #6 cylinder was the problem along with quite a few other things along the way. The problem with a very small headgasket leak is it may not even show up in the leakdown test. Its possible to leak in a fashion that it creates a one way check valve sort of effect. I would say from my experience that the block test is about as 100% as you can get. A combination of all three tests would be, of course, the best route if you are in doubt.

Well, I went out and bought one of those Napa block test kits and had the same results and posted above. Instructions say to leave on and pump air through it for about 1 min. About 45sec into it, the fluid changed from dark blue to a dark blue/green color. I took it to the exhaust pipe and did the same thing and it instantly turned piss yellow. Hate it when things cant just be black and white.

 

[Cman88]

Well, I went out and bought one of those Napa block test kits and had the same results and posted above. Instructions say to leave on and pump air through it for about 1 min. About 45sec into it, the fluid changed from dark blue to a dark blue/green color. I took it to the exhaust pipe and did the same thing and it instantly turned piss yellow. Hate it when things cant just be black and white.

Yeah. I had all the signs, just wanted to use the block tester to "confirm" my thoughts... Like I said, I just tore it down and sure enough, #6 was leaking... had been leaking for a while. I got everything back together yesterday and it runs perfectly now. Temp stays below half mark even in 100+ degree outside heat.