3.4 Compression test

[CCr323]

Hey there everyone, I’m fairly new here and haven’t found anything on compression tests. I just did one on my 98 S/C runner and mine weren’t perfect. I’m no mechanic so I’m not sure how much play should be between them.

Here are my results. I had a fouled plug in cylinder 4 because I was slowly leaking coolant and it burnt out the plug over about 6 months. Is the difference in compression something to be seriously worried about right now or should I just put some thread lock gasket sealer in the coolant. I don’t have the money or time to rebuild it at the moment so I’m looking for the best solution to keep her going.
Any help would be great.
Thanks.

C1 190psi
C2 200psi
C3 180psi
C4 170psi
C5 180psi
C6 200psi

 

[Buckaroo]

You should expect no more than a 10% difference. Based on that, cylinder #4 looks low as you would expect. I don't know what you mean by "thread locker gasket on the coolant." I would replace the #4 spark plug and not use thread sealant on it. I would watch the coolant & oil level closely and see what happens. If it is running ok and not missing, I would drive it....watch the engine temp - it if starts going up that's a problem. If you get engine coolant in the oil, that's not good either but, depending on severity, more of a medium term problem. In any case, not sure how long you can limp along like this.

Buckaroo

 

[Buckaroo]

To clarify - I am not saying your compression test is definitive. There are other tests for head gasket issues. Would suggest looking for bubbles in the radiator with engine running/thermostat open if you think you are seeing cross-over from coolant to exhaust or use something like this.....

https://www.tooltopia.com/uview-560000.aspx

Buckaroo

 

[mtbtim]

You need to perform a leak down test on that #4 cylinder. Once you have the cylinder pressurized, you can then figure out where the pressure is escaping. It's either leaking past the intake valve, exhaust valve, piston rings or out a bad head gasket. With the head gasket, the pressure could be leaking out into a coolant channel but it could also be leaking out into an adjacent cylinder.

There's videos available that show you how to perform a leak down test. Just do a search on YouTube and you'll find several good ones.

 

[gamefreakgc]

Hey there everyone, I’m fairly new here and haven’t found anything on compression tests. I just did one on my 98 S/C runner and mine weren’t perfect. I’m no mechanic so I’m not sure how much play should be between them.

Here are my results. I had a fouled plug in cylinder 4 because I was slowly leaking coolant and it burnt out the plug over about 6 months. Is the difference in compression something to be seriously worried about right now or should I just put some thread lock gasket sealer in the coolant. I don’t have the money or time to rebuild it at the moment so I’m looking for the best solution to keep her going.
Any help would be great.
Thanks.

C1 190psi
C2 200psi
C3 180psi
C4 170psi
C5 180psi
C6 200psi

That's not enough difference to warrant a rebuild. I agree it's not perfect but not terrible either. Your engine won't blow up on you due to low compression, it'll just lose power as it ages.

If you have a leaky head gasket, do it the right way and have it repaired. It will only get worse and those stop leak products are not a long-term fix. It will also coat other components like you radiator, water pump, etc in the rubbery sealant.

One other thing you could look at is your valve clearances, also called a "valve adjustment". An exhaust or intake valve stuck slightly open could be why you are seeing lower compression in a few cylinders.

 

[CCr323]

I put the new plug in and it runs great. It’s been slowly leaking coolant since about August 2017, I fill my overfill resivoir about once a month maybe, but it only leaks mostly when I park it uphill and not start it for a few days and then it just smokes lightly for about 5 seconds and no more after that all day. I was able to look through the plug tubes and see in the cylinder and #4 was way more gunked than others. I would think that isn’t very bad for 300k on it. I would love to tear it apart and rebuild it and throw it in a 1st gen but it’s my DD so I have to keep it running for right now.
Thanks for the reply, I just wasn’t sure how bad the difference psi is. I’ll keep driving it until I get a different one and maybe retire this one. She’s quite the rust bucket

 

[amalik]

That's not enough difference to warrant a rebuild. I agree it's not perfect but not terrible either. Your engine won't blow up on you due to low compression, it'll just lose power as it ages.

If you have a leaky head gasket, do it the right way and have it repaired. It will only get worse and those stop leak products are not a long-term fix. It will also coat other components like you radiator, water pump, etc in the rubbery sealant.

One other thing you could look at is your valve clearances, also called a "valve adjustment". An exhaust or intake valve stuck slightly open could be why you are seeing lower compression in a few cylinders.

If I were in those shoes, I would do a leakdown before paying a mechanic for a valve adjustment. That way, no guessing is involved.

 

[96RedRunner]

Straight out of FSM,

Compression pressure:
1,200 kPa (12.2 kgf/cm2, 174 psi) or more
Minimum pressure: 1,000 kPa (10.2 kgf/cm2, 145 psi)
Difference between each cylinder:
100 kPa (1.0 kgf/cm2, 15 psi) or less

I'd say your looking good for several miles yet.
Have you checked for leaks in coolant system, such as water pump?
Leak down test for sure.

 

[CCr323]

Straight out of FSM,

Compression pressure:
1,200 kPa (12.2 kgf/cm2, 174 psi) or more
Minimum pressure: 1,000 kPa (10.2 kgf/cm2, 145 psi)
Difference between each cylinder:
100 kPa (1.0 kgf/cm2, 15 psi) or less

I'd say your looking good for several miles yet.
Have you checked for leaks in coolant system, such as water pump?
Leak down test for sure.

Yeah, I just finished my timing belt and water pump this weekend actually. What had happened is my plug went out when driving and everyone and every forum I read said my belt slipped and is off timing is why it constantly misfired. I was sceptical but it had been over 90k since it was changed. So I changed the belt and the water pump and started it and it ran the same so I pulled the plugs and found it was the plug. Had no C/E light until after I did the timing belt. Good to know I’m in the clear for a little bit on the compression.

How difficult is it to do the valve adjustments? I’d much rather do it myself or is it something that is just better to pay a mechanic for. I will be doing a leak down test soon and I will post the results. As for now I won’t drive her too hard until then. Thanks again

 

[spartacus]

this probably the best video is a 6 part series


https://youtu.be/voLBRDZL9fE

 

[CCr323]

I started watching them last night lol
I plan to get a 1st gen 4Runner and swap it within the next year so I will probably completely rebuild it then if I get around to doing that.

 

[96RedRunner]

How difficult is it to do the valve adjustments? I’d much rather do it myself or is it something that is just better to pay a mechanic for.

Check out pages EM-4 pg 816 thru EM-8 pg 820 of FSM for valve adjustment. Not hard to do, is time consuming. You will have to measure for shims needed, order shims, wait for shims, finish. That's how I did it anyway not my DD.

 

[phattyduck]

I was able to look through the plug tubes and see in the cylinder and #4 was way more gunked than others.

Coolant leaking into the cylinders actually will CLEAN it, not the other way around. If it is gunked up, it is something else - generally oil getting into the cylinder.

You may have a small coolant leak elsewhere and a bad ring or leaking valve / valve stem seal on the weak cylinder.

-Charlie

 

[4bangr]

I rented a radiator pressure checker from local auto parts store. put it on the radiator, put about 10 psi on it and wait. you'll see where the coolant is escaping. in my case, it was cylinders 1&2. i'd suggest pulling out all the spark plugs in case it is a bad head gasket; you want to see where the coolant is going.

as someone mentioned earlier, coolant in the cyl will 'steam clean' everything in the combustion area. so if you have one plug that's really clean, in comparison to the others, that might be a clue. if you pressurize your radiator, you'll find the leak.

 

[19963.4lsr5]

That's not enough difference to warrant a rebuild. I agree it's not perfect but not terrible either. Your engine won't blow up on you due to low compression, it'll just lose power as it ages.



If you have a leaky head gasket, do it the right way and have it repaired. It will only get worse and those stop leak products are not a long-term fix. It will also coat other components like you radiator, water pump, etc in the rubbery sealant.



One other thing you could look at is your valve clearances, also called a "valve adjustment". An exhaust or intake valve stuck slightly open could be why you are seeing lower compression in a few cylinders.

+100 on checking the valve clearance.

Edit. Look in my 1997 SR5 build and repair thread. I cover valve adjustment.


Sent from my iPhone using Tapatalk

 

[gamefreakgc]

Yeah, I just finished my timing belt and water pump this weekend actually. What had happened is my plug went out when driving and everyone and every forum I read said my belt slipped and is off timing is why it constantly misfired. I was sceptical but it had been over 90k since it was changed. So I changed the belt and the water pump and started it and it ran the same so I pulled the plugs and found it was the plug. Had no C/E light until after I did the timing belt. Good to know I’m in the clear for a little bit on the compression.

How difficult is it to do the valve adjustments? I’d much rather do it myself or is it something that is just better to pay a mechanic for. I will be doing a leak down test soon and I will post the results. As for now I won’t drive her too hard until then. Thanks again

Not hard. The next time you have the engine torn down you can simply measure the clearance between the camshaft lobes when not compressing the valve, and the shim itself. Exhaust has one spec and intake has another, I think it's even printed on the hood on a sticker. If there's any valves with too big of gap (not common) or too little (more common) you take out the shim using the valve adjustment tool, measure the thickness and order a new one with the needed adjustment to thickness bring the gap back into spec.

Don't pay someone to do it though, it takes time, not effort so it'd be a lot of money. Just one thing to rule out. When I first bought my 4runner I was replacing the leaking valve cover gaskets so was a perfect time to do it. Luckily for me every single valve was right in spec so I did not have to change anything.

 

[CCr323]

Thanks, will do since the timing belt kit came with valve gaskets so I’ll get to the valves when I do that. Needs to be done soon anyway since the plug seals are leaking a little oil into the spark plug tubes in C5 & C2.