No start

[BoostedAWD91]

The car wouldnt start fine with very low compression. It would start but its not gonna start very easily with only 30psi of compression. A hot no start issue wouldnt be a coolant temp sensor, that was just replaced to fix the no start issue

 

ive seen many many cars start fine with low compression like that... also a bad coolant temp sensor will lead to hot start problems

 

[vr4play]

Engines don't just go bad. They get progressively worse over time unless something happens to cause a catastrophic failure. I agree that you could have washed the cylinders and you need to add some oil to get the rings to seal properly. Most likely caused by the coolant temp sensor being bad in the first place. With low compression it should run really ruff and sound like it has a big cam. If it purrs like a kitten then the compression is fine once the car is running which could be caused by sticking injectors. You could have a few bad fuel injectors causing the cylinders to wash out. Did you unplug the ecu fuse and fuel pump so that no fuel could enter the cylinder while doing the compression check. Also the coolant temp sensor to the ecu is in front of the t-stat housing not on top. The one on top turns off the A/C compressor when it senses the engine over heating. Make sure you repaired the correct one.

 

[BoostedAWD91]

yeah well the previous owner "rebuilt" the engine himself and he just pretty much threw it together and didnt do it correctly so it wasnt in the best of shape to begin with. The compression wasnt perfect or excellent for that matter when i tested it 1.5 years ago when i bought the car so i wasnt expecting it to last forever honestly. i understand that when the Coolant temp sensor was bad it was just dumping gas in and washing all the oil off. The last compression test which the results were very very low was 1-2 weeks after replacing the temp sensor so it should of gotten oil back in the cylinders. I also did put some oil in the cylinders while doing the test to see if it helped at all and it didnt. I have a DSM thermostat housing in my car which is alittle different than the galants. Both the sensor and harness were replaced for the sensor. I do not have A/C in the car anymore so that sensor isnt there anymore

 

[ktmrider]

Ok, the info about adding oil to the cylinders and repeating the compression test helps.
No change to the results with oil "usually" points to a timing problem ( bent or hanging valves ). It was asked quite a few times and I scanned the posts but DID you check the timing marks yet? Bad timing will also cause the hard/no start symptom.
It'll take 5 minutes to align the crank mark and check the cam gears if you have not done so...