How to determine TDC for LeakDown Test

[eric4welches]

I have a coolant leak that I'm trying to track down. I fill up my reservoir but the level is not maintained. I don't see any mixing in the oil. I decided to try my hand at a leak down test. I do the typical YouTube search - seems pretty straight forward. When it comes to actually performing the test, I find it very difficult to determine exact TDC on the compression stroke. I can find the compression stroke fine using the balloon test. I just can't figure out how dial in when both valves are closed. Can I do this electrically? Maybe connecting the negative and positive battery leads (without the battery in the connected between of coarse). Then measure voltage between the spark plug cables and the the engine? Heck, I don't know.

BTW - My X is a 1992 4.0 XLT. w/4WD, Automatic.

Thanks for your suggestions.

 

[natenkiki2004]

For that, you don't have to be 100% at TDC. As long as you're halfway up or towards the top of the compression stroke, the valves should be plenty closed by then and it should be sealed. The only reason you'd want it at TDC perfectly is to eliminate cracks in the block from messing with your valve/head leak test. I've never read of anyone cracking a block in these Explorers.