the results of the compression test are in!

[NiceGuyEddie]

this test was done per request of the forum, in the event that a blown header gasket may be the source of my overheating problem.

i am not sure if i numbered the cylinders the offical way to number a ford engine. the compression tester gauge was brand new. i hope i did the test correctly -- i turned the key about 5 seconds each time. i took three readings for each cylinder. yes, i remembered to release the pressure before each reading. the readings are in psi, obviously. i felt like i was back in engineering school!

my engine is a 302, .030 over, stock crank and stock compression. mild cam if that matters. fresh 10W40 quaker state oil. the engine has about 100 miles on it, but the plugs have about 60 highway miles on them.

all the spark plugs looked the same, except the #5 plug shown on the left. as you can see in the photo, it a little brown on the tip. you can't see it in the photo, but the brown color is also on the metal "nut" part. there is also a significant carbon deposit on the header flange in the #5 position. maybe i had the spark plug loose?

so how do i look?

[nc1mike]

Those readings are consistant enough. On a Ford a blown head gasket is hard to tell with just a compression test, unless it is a catastophic failure. A leak down test is better. The cam you are running must have a lot of overlap those psi readings are consistantly low, I would expect in region of 165psi. Your driveabillity issues might be from too big a cam and not enough static compression. The plug gaps looks kind of wide too, but they look ok. To properly read a plug you need to look at the ring of the base of the threaded portion. Let's see what the others have to say.
Michael S.

[NiceGuyEddie]

Michael:

do you mind repeating that first part in english?

[nc1mike]

Getting back to your original issue. The rapid coolant expulsion, I haven't had any experience with it. Your other thread on filling the cooling system seems like it went more like normal this time. My cooling system has never needed any attention since the first fill, no burping, nothing...It exchanges maybe a pint from hot to stone cold thru the expansion tank. Have you thought of placing a pressure gauge say 0-20 psi in the intake manifolds water jacket bung that you have a threaded plug in? This would be telling since the cooling system shouldn't go over 16psi on a normal basis. You could tape the gauge to the dash and go for a test drive and monitor the cooling systems pressure. Just a thought.
Michael S.

[nc1mike]

Eddie, in reply to you request.
Readings are consistant in pressure spread. No indication of failure.
The classic blown head gasket usually has 2 adjoining cylinders with low pressure.
The cam overlap refers to the intake/exhaust phases of the cams grind overlapping and thus causing lower static compression. This is a crap explanation...Essentially with a big cam you need high static compression.

Put it together and drive it...See if it acts any different than before.
Michael S.
plugs are read by looking at the round end not a side view so much

[baumann]

Just something to consider: if you don't have a heater (and most of us don't) you may wish to find a way to still connect the heater loop - with a suitable flow restrictor.

I was having a weird problem with my cooling system: On startup (with 180deg thermostat) indicated temperature would show 175.. 180.. 180..195..210...225..250!!!..210...210..210..
In other words, slow climb to 180.. hold for bit, then rocket up to 250, and then slide back down to around 210, where it would hold. No massive belching of coolant, no obvious signs of overheating. System wouldn't suck up any new coolant from the overflow, nor take any more from the filler neck.

Built a system to pull a vacuum on the cooling system - and got a major bubble out (to the tune of about 1.5quarts) - but still had the same problem.

Plumbed the heater line back in (I'd dead-headed it trying to clean up my engine compartment) - and I now run at a constant 190ish (hard to tell the exact amount not enough marks on the gauge) Speculation on my part: I had small air bubbles trapped in the intake manifold that couldn't find their way out without the added flow from the heater port.

[NiceGuyEddie]

Michael S quote:

The classic blown head gasket usually has 2 adjoining cylinders with low pressure.

ah-ha! the light just went on.

yes, i have a heater. i have the 1/8" hole in th e thermostat now. when i filled up the system, it was totally different. i could have sworn the engine was burping and bubbling from the radiator AND engine side. last time i think it was just burping from the radiator side.

i suppose the vacuum test is next.

[imacobrabuilder]

Is the engine still overheating, or are you still trying to correct a problem from before? Has the engine overheated since starting it up again? The compression variance between cylinders looks good.

If not, maybe it was simply a faulty thermostat?

Good luck.

You shouldn't have to go through all of this stuff - especially with a professionally rebuilt engine. Now me, I rebuilt my own engine... We'll see if it runs in a month or so...

[NiceGuyEddie]

startup should be coming in the next 36 hours. it just topped 109º in my garage, so i jumped into the pool (bath tub).

[6243]

I had a blown head gasket on a freshly rebuilt 302, and it was manifesting itself by overflowing the recovery reservoir when I'd put my foot in it. It would never recover. I had a blown head gasket between #6 and #7; not bad enough for a compression test to show anything. I had a consistent 155 to 158 PSI on all cylinders. Another part of my problem was that I reused the stock head bolts; the heads were effectively lifting off the block under hard acceleration and blowing out into a water passage, and compressing the coolant system.

If you are having issues, just pull the heads, replace the gaskets with good Fel-Pro gaskets (I used 1011-2's at the recommendation of Richard Oben, but $40 apiece), and new head bolts. You'll likely never have a problem with head gaskets again, and you can for sure eliminate that as part of your problem. It's really not a hard repair. I had about 2 hours in teardown and 2.5 in rebuild, including filling the coolant system. Problem went away after that, and now I know I have a solid platform for a blower down the road!

HTH,

Greg

[NiceGuyEddie]

Greg,

last time it overheated, like your story, it happened immediately after i punched it.

i drove it for about 20 minutes up a huge hill, down a hill, on the freeway. i got off an exit on the freeway to turn around. i hit it hard on the other entrance ramp. at about 5000rpm, there was a loud snap, crackle, and pop backfire, so i layed off the throttle. 45 seconds down the road, the engine got really hot, antifreeze spewed out, and i limped it home.

[nc1mike]

Eddie that's a blown head gasket to a coolant passage not to an adjacent cylinder.....
Michael S.

[NiceGuyEddie]

...yes, i understand that it's pumping air to a coolant passage. so the compression test does not necessarilly prove that i am okay, right?

[Big Blocker]

Eddie,

Go to the local parts store and see if they rent or loan out a compression gas tester for your coolent system.

It checks for carbon monoxide (the major by-product of combustion) in your coolant. Liquid indicator turns green from blue if there is carbon monoxide in your coolant, indicating that you have a blown head gasket leaking into your water jackets.

Also, the above suggestion about connecting a pressure gauge to your system is the best way to see if the cooling system is being pressurized by compression.

good luck . . .

You have my utmost admiration . . . your problems with your flywheel/starter, and your persistance to see it through have given us all a boost of confidence.

Doc [img]graemlins/fire.gif[/img] [img]graemlins/fire.gif[/img] [img]graemlins/blue2.gif[/img]

[nc1mike]

Eddie, that's correct. A hot compression test as apposed to the cold compression test might show a problem. A leakdown test might pinpoint it also. However you are dealing with a SBF and this is how they fail. When the engine get hot the bolts stretch or the head lifts ever so slightly and you get a shot of coolant, bang, pop, shot of hot compression gasses back into the cooling system. When it cools it masks the problem as it reseals partially. If you are using stock head bolt you will need new ones, the stock are a one time use only. This is the cause of most failures, reusing stock head bolts "Torque to yield" but only once. If you have ARP they can be reused. Also you will need head gaskets and intake manifold gaskets. Hope those new exhaust manifold gasket are reuseable if you already installed them.
Michael S.

[Porxter]

Hi Eddie,

As was previously stated, the close readings between all cylinders is a good sign. However, the reason they may be lower than expected may be caused if you didn't hold the throttle wide open during the compression tests. That is the proper way to do a compression test.

And yes, you numbered it right for a Ford.

Steve

[hind sight]

Agree with the others on results of the compression test. Although they are a bit low,could be caused by throtle being closed during test,not cranking motor long enough since it should be cranked till needle no longer climbs. Main thing you are looking for here is all cylinders are reading the same psi which yours pretty much are. Cooling system test is needed now. This low of a compression could also be a sign of retarted cam timing. Lets hope it was only in way test was done.
Plug on left could have been a bit loose. Notice how the metal base is no longer bright shiney silver color but has the "blueing" color indicating it got hot from not being able to transfer its heat thru base into head. Was this plug too easy to remove? To read a plug you need to look down into it not at the side. Tip of insulator along with where the ceramic meets base, and also bottom of metal threads. These areas of the plug tell what happens when engine is running. Tip of insulator for signs of detonation/pre ignition. Base of insulator for heat and contaminates reading, such as you would see if anti freeze or fuel addadives being burnt. Bottom of threads or ring for the mixture reading.

[NiceGuyEddie]

UPDATE::

i just re-did the test for ONE cylinder. this time, i cranked it for TEN seconds, not three or four seconds. the reading was 157psi. i did this to another cylinder, and got about the same result.

i guess i didn't crank it long enough. maybe it takes a few seconds for the oil pressure to build up? just a guess. i didn't have time to do all the rest, but i think it is safe to assume all is okay.

[hind sight]

Think you are fine. Haveing the numbers a little higher is a good thing but major comparison wanting to see is they are all close to reading the same amount. Hopefully all problems will be able to get corrected with a good tune. I suspect distributor is going to come into guestion when tuner gets the car.

[CraigS]

As a reference for the future-crank each cylinder til the gauge stops going up.For the odd situation that this may mask,you will get a feeling for normal amount of cranking after 8 cylinders.If one takes longer that could indicate a problem even if the number is OK.Good luck