08 GX 470 Low Compression (1 Viewer)

[FranklinRd]

Long time listener first time caller

Persistent cylinder 3 misfire on the new to me 190k GX. Bought it in July and after 1k miles of ownership the check engine light came on. Only code was misfire cylinder 3. Replaced #3 coil and all 8 spark plugs with correct Denso coil and plugs. Fast forward another 1k miles and light came back. Same cylinder misfire. Performed compression test and found left bank issues. #1 at 120, #3 at 92 and #5 at 100. All others between 170-180 psi. Added Marvel Mystery oil to crank case, Seafoam top end clean and Techron in the tank. Fault came back a few hundred miles later. Going to recheck compression and preform a leak down this weekend. Thoughts? Having come out of a 3rd Gen Tacoma I didn’t expect engine issues from this era truck.

 

[Jstawgn]

Should not happen on properly maintained vehicle but who knows what kind of maintenance PO did. First and second owner might take care of or good. Back in 2015-2020 GX are dirt cheap in used market and it attract a lot of lower income customers. Mainenace labor are expensive and these customers deferred maintenance a lot.

Try Valvoline restore and protect to try cleaning the piston rings. Relatively lower on 3 cylinders might indicate small head gasket leak.

 

[Rednexus]

I'm wondering if it was overheated by a PO and had head gasket issues. The radiators in these are known for cracking and leaking. If it was driven on low coolant it could certainly explain low compression in multiple cylinders.

 

[stupidchicken03]

I was thinking head gasket as well since that whole bank is noticeably lower than the other.

 

[Poop Bubbles]

What type of coolant was in it?

 

[aztoytec]

Have a cylinder leak down test down. This will tell you where the compression is going. May have a couple bent valves and/or head gasket.

 

[FranklinRd]

All good food for thought. Saturday I’ll compression, leak down and use a combustion gas detector and put a plan together. It’s due for a timing belt and the intake needs to be resealed, adaptation values all out of wack. Why not add in a pair of head gaskets and the “while you’re in there” items. Thanks for the feedback thus far.

 

[Poop Bubbles]

All good food for thought. Saturday I’ll compression, leak down and use a combustion gas detector and put a plan together. It’s due for a timing belt and the intake needs to be resealed, adaptation values all out of wack. Why not add in a pair of head gaskets and the “while you’re in there” items. Thanks for the feedback thus far.

Head gaskets are considerably more work, but it seems you likely need them. Good on you for proper diagnosis. Stick with the OEM/Aisin timing/WP kit.

I ask about coolant type because dumbass previous owners often put green, orange etc. non-comforming coolant in which I think over time can erode a head gasket if not changed frequently. When re-installing, use only Toyota long-life coolant. It should last 100k and not cause issues with OEM gaskets.

"While you are in there";
- Consider a new OEM/Denso starter, as they are super hard to get to. They rarely fail, but when they do it sucks to replace.
- It's also a good idea to do new OEM/Denso radiator and alternator. Those do seem to wear out at 150-200k, the alternator is also particularly difficult to access and catches a lot of road water/mud given its location. If you can't find evidence those were replaced, it's a good idea.
- Leaking exhaust manifolds are also another common issue. Again, much easier to get to if you are doing all that other work, especially if you are removing them anyway to work on heads. Consider long tube headers & yotawerx tune if you do not have emissions. Really makes a nice power difference.

 

[FranklinRd]

Ok so did three things today. Used a combustion leak detector at the radiator neck, no issue there. (Appears to be correct red Toyota coolant). Rechecked compression, no real change. Still #1 105psi, #2 90 psi, #3 105 psi. Performed a leakdown test. All three are awful, 50+% leakage. All leakage appears to be from the exhaust side. Thinking cheap route of pull left head, check for damage and just address the valves. I have a timing belt kit, etc. put it back together and rock on/hope for the best. Trucks condition overall is fair to good w/ 190k. A replacement engine is also a good option but plenty of other things need love. Let me know your thoughts.

 

[aztoytec]

Sounds like a good plan. Curious if it had a timing belt break on it in the past causing damage to the valves. Rare occurrence but possible.

 

[FranklinRd]

Sounds like a good plan. Curious if it had a timing belt break on it in the past causing damage to the valves. Rare occurrence but possible.

Sounds like a good plan. Curious if it had a timing belt break on it in the past causing damage to the valves. Rare occurrence but possible.

It’s hard to know if that occurred with a previous owner. Given the evidence of bad/lazy techs who have worked on it in the past anything is possible.