Compression test results interpretation


#1

My '98 honda civic with around 140,000 miles overheated from a cracked radiator and I need to know if the compression test results #1-120psi #2-70psi #3-90psi and #4-120psi indicate engine damage, because the mechanic I dealt with said it was impossible to determine and he said while it was outside the ideal 10% range it was probably ok but impossible to know for sure.
They performed a wet test on #2 and said pressure went up from 70 to 90psi. I think he misled me by saying while the test results were not ideal they did not mean there was engine damage either. He said the radiator could be repaired and I would need to keep on eye on the temperature. I was worried about damage to a head gasket he said he did not think so and after I pressed him on it he said if anything there may have been damage to a piston ring because of the wet test result on #2. I had the radiator repaired because of the way he interpreted the results to me and a few days the later the car refuses to turn over. It doesn’t sound like a battery issue I can hear the engine try to turn obviously there was serious engine damage done and I would like some advice on how to proceed. Thanks


#2

Considering your Honda is 19 years old, overheated and failed a compression test, This engine clearly has a problem that can’t be solved without at least pulling the head and repairing either a cracked head or blown head gasket, or worse. I’d say it is destined for the junkyard unless a rebuilt head will cure the problem which I doubt at this point since it won’t even turn over. I can’t imagine its worth the cost of a rebuilt engine or even a used engine IF you could find one.

I think your mechanic is covering his rear since he should have done the compression test before he spent time and money changing the radiator. I think he owes you the cost of the radiator. To be fair, he deserves to be paid for the compression test.


#3

Just a wild guess here. Your head is warped and the head gasket blown. Remove the spark plugs and attempt to crank the engine. If water blows out of cylinders 2 and 3 my guess is correct.


#4

Thanks for the reply. He did do the compression test before and the reason
I am upset is he interpreted the results as saying the car was fixable and
the compression test results did not indicate serious engine damage. He
said there was a chance but it was impossible to tell.

I agree that it is fair to pay him for the test and inspection


#5

Even the “good” cylinders are pretty low.
Probably worn rings & cylinders.
A wet test of #1 or #4 would probably bring it up to 160-180, where it belongs.
Time to find a used engine, if it’s worth the effort to you.
There are places that specialize in used Japanese engines.


#6

Even the highest numbers are way low and the engine likely has piston ring/cylinder wall damage.


#7

Thanks for the responses I was also wondering if the mechanic was being dishonest with me. I certainly think so now. I doubt I want to put more money in it but not really wanting to buy another car. I’ve been looking at some Mazda2s.


#8

The compression spec’s I’m seeing for a 98 Civic w/the 1.6L engine are around 185 psi nominal, 135 psi minimum acceptable, and no more than 30 psi variation between cylinders. That’s about the same specs as for my 1.6L Corolla coincidentally . So if I got those measurements on my Corolla anyway, I wouldn’t have interpreted them as ambiguous, but definitely indicating a problem. But that wouldn’t necessarily indicate that it is a ruined engine either. More investigation would be needed to determine the prognosis. The possibility that the compression readings are inaccurate due to faulty test equipment and/or test method should be considered too. But my guess is those are accurate readings, the engine was damaged by the overheating incident, and the cylinder head is goint to have to come off before you’ll know for sure what’s going on. Does it remain drivable? Or does the engine run so poorly you can’t drive it? If the problem preventing you from driving it is that it won’t crank, no-cranks are usually pretty easy for a shop to figure out. They’d probably start by trying to manually rotate the engine using a socket on the crankshaft pulley bolt.


#9

Thanks George. It won’t crank and I’m not sure if I want to try and get the
car fixed or send it off to the junkyard. I have been looking for a good
mechanic to trust around here and am not sure where to go. What really irks
me was his ambiguous interpretation and the more I learn about this the
more it seems that no mechanic would think there were no issues with those
kind of readings. I should have done a better job of doing my due diligence
at the time but the shop was recommended to me so I felt more comfortable
going with his advice. Do you think I have a good standing to ask for my
money back? I doubt I would get it but I think I should take it up with
them before I complain to other sources like BBB etc.


#10

For me, life is too short for all that. I wouldn’t be asking for any refunds. But I would want to discuss the apparent discrepancy between what Honda says the compression specs are, and what the mechanic says. There may be a reasonable explanation, so I wouldn’t myself want to engage in unwarranted accusations. I’d want to let the shop have a chance to explain. If I wasn’t satisfied with their explanation, I’ just use a different shop next time 'round. After all they aren’t the reason the car overheated, right?

For a little perspective, my Corolla is 6 years older than your Honda, similar engines, and at about the same age as your Honda the radiator fan stopped working and it overheated and the pressure busted the top of the radiator. The only reason I noticed when it happened, there was a lot of steam coming from the front of the car, which I first thought was just normal San Francisco fog. In my case I eventually realized it was the radiator and stopped the engine in time.


#11

The reason for the the overheating was a radiator malfunction and is a
separate issue from either an incompetent or dishonest mechanic. If you
broke your leg woul
d that excuse a doctor from malpractice?


#12

Did you try removing the spark lugs and then turning it over… if the starter motor won’t do it, you can access the harmonic balancer (crankshaft) nut at the left front wheel well and try turning it with a breaker bar…


#13

hmm … well in the example of the doctor which you propose, if the doctor said he thought it was a sprain, but a follow-up test proved there was a hairline crack, as long as the doctor’s incorrect first diagnosis didn’t cause me any severe add’l damage, I wouldn’t ask for a refund for the first diagnosis. I might ask why the doctor thought it was a sprain tho, to try to understand why he thought that, and to give him a chance to explain his reasoning.


#14

With those compression values you should have been advised to not drive the car without repairing the damage to the cylinder head and head gasket, you will soon be a pedestrian.

How much do they charge for a misdiagnosis? I would expect no more than $125 from an independent shop, we charge $90 for a misdiagnosis (the talent varies greatly in the shop).

How did you find someone to repair an old plastic radiator? New replacement radiators are $100-150, only about $50 if you do the job yourself.


#15

Sometimes you get ambiguous results, Keith. Would you rather he speak with a certainty that he can’t back up? A low reading on adjacent cylinders, following an overheat COULD be “just” a HG; probably more likely the head is also warped; and POSSIBLY a cracked head! (And you typically can’t tell until you disassemble.)

I’d sooner somebody err on the side of being too ambiguous, not too certain: give me ALL the possibilities, however remote, and I’ll decide how I want to play it from there.


#16

He didn’t say head gasket or anything else. He said probably just the
radiator- engine is probably fine. My point is that a mechanic should know
based on those numbers that something was wrong with the engine and tell me
that although he can’t say what it is without further inspection something
is definitely wrong.


#17

It’s been my experience that when compression is low across the board in all cylinders there’s a cylinder issue (rings, glazed/scored cylinders, seized rings, or rings have lost their temper (meaning springiness not attitude).

A wet test should be performed on all cylinders. The fact that No. 2 went up 20 PSI points to rings on that one alone. One cylinder or all; when the cylinder bore is affected it means major repairs.


#18

When adjacent cylinders are drastically low following an over heated condition it’s best to assume cylinder head/gasket failure until determined otherwise in my experience. But then when any one cylinder is below 110psi and the valve train is OK the engine needs to be opened. Most engines will dead miss at idle on cylinders <100 psi.