2004 4Runner - 1 cyl low compression

[meep]

If I recall, that era of Toyota 6’s had the occasional issue with burning exhaust valves. Or it may have been the prior decade. A simple head R&R would be the fix there, and frankly, if the rest of the block is in good shape, would be my preference. if it’s been well maintained, I’d much rather keep the rest of my known good engine block than swap with a reman. Knock out timing belts, water pump, front seals while you’re in there.

the mechanic may identify a full reman is the same cost as the labor may be less to just swap them out. In that case, it would be hard to justify spending more than that at the age of the vehicle.

 

[wtd]

He should find someone with a pressure transducer to put in the low cylinder. They should be able to tell if it's a valve issue and which one.

 

[paulo57509]

Other than that nagging feeling that it isn't "right", is the one low compression cylinder causing any obvious drivability/performance issues?

It's a 20 year old, relatively high mileage car. Unless the owner plans on keeping it long term, I would forgo sinking money into it and just do regular maintenance and drive it.

 

[AZjeff]

The owner has no plans to replace it anytime soon. He and wife like it and are willing to fix it.

 

[supton]

60psi seems crazy low. I'd do a bit more work to examine why. Chipped valve, or scored cylinder? I'd think a scored cylinder would show as high oil usage, fouled plug and dirty oil... although now that I think about it, it's probably easier to just replace the motor--chipped valve or bad bore, end result, faster to swap the whole motor.

I'm less worried about diffs and transfer case, those seem long lived. Trans, now that is a wild card. But it's an Aisin, which isn't to say it'll last forever--but they do tend to go long. Might be just best to swap the engine. If the trans dies next year... less than a car payment, right?

 

[Plawan]

well these day, repairing our older high mileage cars makes a lot more sense than before the cost of cars and everything doubled.

 

[ARCOgraphite]

No way it's past its expected service life. That's rust belt conditioned thinking.

I meant the engine. I just rebuilt the 340 hi-po engine a 67 buick GS a couple years ago. along with replacing control arm and sway bushing and ball joints. Drives great.

 

[ARCOgraphite]

I see that engine (5VZFE) has a DOHC S.U.B. 4V heads. Might have a recessed and tight EX valve that can lead to melting/burning of part of the seat circumference.

 

[meep]

I’ve worked with a lot of Toyotas over the years. They became very particular about their engine metallurgy in the beginning, and one result I’ve seen over the years from it is the cylinder bores simply don’t wear much. Im not sure if it’s related, but when they first formed, they sent their engineers to Mercedes mechanic schooling since they were well renowned for robustness. You could see similarities in the old 20R and 22R engines, which looked really similar to a Benz engine in the 70s. Castings, double roller timing chains, and other features looked similar. a local landcruiser specialty shop run by a fanatic/friend of mine told me that their engine metal porosity (on the microscope level) is intentionally much lower than the norm. I pulled a 300k miles Toyota I6 with him that measured still in spec with no cylinder ridge of any consequence in them. The blocks are solid unless mistreated.

the heads, on the other hand, as I mentioned above, have had some exh valve issues from time to time.

i just helped my son do the brakes on his 2019 4Runner. I learned that they don’t use vacuum for brake boost in his year, it looks like it is hydraulically boosted. I’ve never seen that on less than a 3/4 ton truck. 4 piston calipers up front (which seems pretty standard for them).

if someone wants to keep a 4Runner going, it’s probably worth it.

 

[AZjeff]

I see that engine (5VZFE) has a DOHC S.U.B. 4V heads. Might have a recessed and tight EX valve that can lead to melting/burning of part of the seat circumference.

I think this is what the 2nd mechanic is looking for next week with a borescope.

 

[D60]

I’ve worked with a lot of Toyotas over the years. They became very particular about their engine metallurgy in the beginning, and one result I’ve seen over the years from it is the cylinder bores simply don’t wear much. Im not sure if it’s related, but when they first formed, they sent their engineers to Mercedes mechanic schooling since they were well renowned for robustness. You could see similarities in the old 20R and 22R engines, which looked really similar to a Benz engine in the 70s. Castings, double roller timing chains, and other features looked similar. a local landcruiser specialty shop run by a fanatic/friend of mine told me that their engine metal porosity (on the microscope level) is intentionally much lower than the norm. I pulled a 300k miles Toyota I6 with him that measured still in spec with no cylinder ridge of any consequence in them. The blocks are solid unless mistreated.

the heads, on the other hand, as I mentioned above, have had some exh valve issues from time to time.

i just helped my son do the brakes on his 2019 4Runner. I learned that they don’t use vacuum for brake boost in his year, it looks like it is hydraulically boosted. I’ve never seen that on less than a 3/4 ton truck. 4 piston calipers up front (which seems pretty standard for them).

if someone wants to keep a 4Runner going, it’s probably worth it.

GM ran hydroboost on plenty of 1/2 tons, particularly in the GMT800 platform. Maybe GMT900s too?

And while far from the pinnacle of reliable engineering, Audi used hydroboost in sedans and avants, at least in the early '90s, which is as late as my knowledge of that marque goes.

I'm sure there are other examples of cars and cute utes that employed hydroboost. Sometimes it's simply a space constraint as a vacuum booster occupies a fair bit of real estate, esp in today's engine bays

 

[dogememe]

GM ran hydroboost on plenty of 1/2 tons, particularly in the GMT800 platform. Maybe GMT900s too?

And while far from the pinnacle of reliable engineering, Audi used hydroboost in sedans and avants, at least in the early '90s, which is as late as my knowledge of that marque goes.

I'm sure there are other examples of cars and cute utes that employed hydroboost. Sometimes it's simply a space constraint as a vacuum booster occupies a fair bit of real estate, esp in today's engine bays

On the flip side, how do they do hydroboost on stuff with electric power steering? I understand some EPS still have fluid (Nissan?) but some (Ford Escape, for example) have no fluid at all.

 

[Wingo]

If he wants to try mechanic in a bottle, Restore has worked for me in the past to bring compression back up.

 

[addyguy]

I was going to suggest trying Restore oil additive as well.

 

[dumkid]

On the flip side, how do they do hydroboost on stuff with electric power steering? I understand some EPS still have fluid (Nissan?) but some (Ford Escape, for example) have no fluid at all.

Electric hydro boost, basically there's a electric pump and accumulator instead of a belt driven pump or diaphragm. Some Toyotas and Mitsubishis use this design.

 

[AZjeff]

UPDATE: The 2nd indie borescoped it yesterday and found a cracked valve. Owner saw it as well. Didn't tell me if there was any other visible damage to the head. He's decided to have reman heads put on and hope for another 100k. He and wife like the vehicle and aren't interested in something else.

 

[Chris142]

Valve adjustment?

 

[AZjeff]

Valve adjustment?

Asking if it was out of adjustment or can a new valve be installed and adjusted instead of new heads or what?? Don't have any more details at this time.

I think I'd fix exactly what needs fixed and carry on or sell it on a 20 YO/230k car but he's a Toyota Fan Boy. It's kinda killing him that his beloved Toyota has failed him at such low mileage.

 

[paulo57509]

UPDATE: The 2nd indie borescoped it yesterday and found a cracked valve. Owner saw it as well. Didn't tell me if there was any other visible damage to the head. He's decided to have reman heads put on and hope for another 100k. He and wife like the vehicle and aren't interested in something else.

I think this is the best route. Resist the urge to start looking for other things to fix.

 

[meep]

A single valve can be replaced but the seating and lapping of it is a little bit of an art that I’ll bet a lot of mechanics no longer do. But, as I mentioned before I think, this failure is a bit of a tendency with these heads. Smart money is on new heads with valves, as another might not be far behind.