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At 1800 ft and 115psi compression Id redo the top end that was hot max I would let it go too 120 cold. There are two general ways of testing the compression on a gasoline engine.
Testing cold works to as all you are trying to do is get an indication of what is going on inside.
Should engine compression test be done hot or cold. In a no start condition obviously the test is going to be done cold. It is still information and will exhibit gross problems. If the engine appears to have a serious problem and all you are looking for is a gross problem like a blown head gasket or burnt valve do the test cold.
When you crank the engine keep away from the spark plug mounting holes. If a compression measurement is performed with water oil fuel etc. In the cylinder due to the cracks in the cylinders these substances heated to a very high temperature will blow off the spark plug mounting holes and could be dangerous.
I took a compression test on one cylinder this morning stone cold and then dead hot after 12 hours running to verify the assertions. My assumption was that the reading would be more accurate under operating conditions. That taking the compression cold would give false indications and that the compression would be lower with engine hot.
For a really accurate test the engine should be at operating temperature but Ive done the same engine hot and cold and only noticed a couple of psi difference. The one wet cylinder will give you an inaccurate reading. Thus cold compression testing vs.
Hot compression testing will yield totally different results especially on an engine with problems. Not only will the compression generally rise with a hot engine but anomalies and of cylinder differential will change. No good mechanic does cold compression tests.
A hot test using the differential pressure testing method is preferred and will indicate where the loss is occuring. Of course you had all the spark plugs removed and the carb venturi full open when you did the test. Using the hot cranking method and letting the cylinders pump 5-8 times your readings are acceptable.
There are two general ways of testing the compression on a gasoline engine. The process involves the use of a manual hand-held compression gauge รข The test must only be done on a properly warmed up engine. A cold engine will give erroneous results.
I know that the engine should be run prior to leakdown as when the engine is warm everything expands and the leakdowncompression should be better. But Ive also read getting cold numbers and hot numbers is a good idea. However all the searches i do on this forum and google dont show the difference between a hot and cold leakdown test.
Ive done diesel compression tests on both cold and warm engines and the warm readings were always better so yours should be fine. Email protected SOLD 1984 F-250 4x4 C6 BW1345 354 D70 XLT extra cab box-stock so far. A cold engines pistons and rings wont have experienced thermal expansion so a cold compression test could be more truthful about the bottom ends real condition.
Compression test each cylinder cold and identify any that gives an inconsistently low reading. Squirt a small quantity of oil into the cylinder through the. This is not absolutely necessary however and the test can certainly be done with the engine cold.
The test results will not vary in my experience anyway all that much. I even ran across one site Duncan Racing International which claims leak down tests should only be done cold. October 20 2020 at 945 pm 218985.
Testing warm will give a truer reading than testing cold as all the parts will be at their operating clearances. Testing cold works to as all you are trying to do is get an indication of what is going on inside. Hi All When doing compression tests in the past I have always removed all the spark plugs at the start and then tested each cylinder in turn.
I mentioned this to a mate recently and he told me that you should only remove the spark plug from the cylinder that is being tested and leave the rest in situ. Engine Compression Testing. Back to basics Aviation Pros.
Take a look at the dynomo joe web site he has a really good post on engine fitness on there. Plus pending on you elevation it will give you different readings at sea level or 4000 ft with the same sled etc. At 1800 ft and 115psi compression Id redo the top end that was hot max I would let it go too 120 cold.
How do you perform a compression test. The process to perform this test is really easy. The engine should be HOT during testing.
If you are working on a non-running motorcycle you can test while cold however values can be 10-15psi lower in some cases. Piston rings valve seats and other critical components are designed to expand as they heat which creates the desired compression ratio inside the engine. If you complete a compression test on a cold engine the reading will be inaccurate.
Completely shut off the engine. To complete a compression test the engine needs to be shut off. Technically You should do this when the engine is hot but I dont like burning my fingers so I always do it when the engine is cold.
A hot engine would probably read a few pounds more but a cold reading will tell you what you need to know. Run the test on each cylinder. All the cylinders on an engine should be within ten pounds of each other.
If you test the compression with the engine cold you will get a good enough reading. If you test it warm it should be about the same. That is the running compression.
Most motors that have a hard time starting when they are warm is because the compression is too low. Worn rings is the main cause of this. How To Do A Compression Test Dry Start with a warm engine the ignition and fuel disabled and all spark plugs removed.
In addition always wear protective clothing and gloves while working around a hot engine. You might also want to invest in some quality steel toe welding boots to protect your feet. Especially if your vehicle requires welding.