Engine rebuild, swap, or neither? Advice needed

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I'm troubleshooting, and would welcome suggestions on next steps.

This is my first time to troubleshoot something like this, so don't hesitate to let me know if I'm headed the wrong direction somewhere.

1997 4runner, 275,000 miles
5FVZE engine, manual transmission

Needs a valve cover job pretty bad, I'm leaking a quart every 1500 miles or so.
Also losing coolant somewhere, maybe 2 quarts in 5000 miles.
Reduced power output compared to my Tacoma with the same engine.

Today I did a compression test, and a leakdown test. Here are the results by cylinder:
Compression
1 - 155psi
2 - 150
3 - 137
4 - 143
5 - 144
6 - 160
Leakdown test from 100PSI
1 - 74psi
2 - 78
3 - 51
4 - 56
5 - 60
6 - 86

Air during leakdown test may be escaping thru the throttle body. The sound changes when I open/ close the throttle.

So, what do we think about this motor? Is there any reason to consider valve cover gaskets without rebuilding the top end? Are there other tests I should perform?

I've never rebuilt a motor before. Is buying a rebuilt motor and swapped that in a more reasonable task for a novice mechanic?

 

[brillo_76]

Adjust the valves. The Issue is that is a not really a novice project. The issue is that they are the bucket type and quite the project. Tim has videos on it. The window is 250K to 300K as enough time that the valves need checked.

Unless you have a head gaskets leaking, which can be tested with a coolant leak-down test on the cylinders. Its possibly the valves.

The 5VZ-FE is not known for ring issues, possible but extremely rare.

 

[1blink]

Thanks for the input!

How does a coolant leak down test vary from the standard leak down test that I performed? I've done some searching for the last little bit, I'm coming up dry on that.

Are we not that concerned about the border line low compression numbers?

I'll read up on the valve adjustment process to see if that's something I could tackle. You think that is where my leakdown test air is escaping?

 

[brillo_76]

If you head gaskets, have some leakage you see it in the coolant leak down test. Provided you don't have any leaks anywhere. As a leak, somewhere will not give you accurate tests.


When you pressure the cylinder with air are you seeing any bubbles in your radiator? As it will go both ways.

My guess is you have a few tight exhaust valves..


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[1blink]

There was no sign of bubbles in the radiator when I did a leak down test on the cylinders.

 

[nissanh]

Would you consider to do a cylinder head job? I have never done such, until I blew the headgaskets in my 92 prizm (had a bad alternator/water pump belt and it snapped when I am at 75 MPH). I took the heads to a shop, they did a complete job for $ 270 (in 2013): this includes new valve seals, resurfacing mating surface and resurfacing the valves/leak test. The shop also got the proper shims on intake and exhaust valves (or I thought they did). I got all installed, spun the engine by hand to check timing.. started the engine: I immediately noticed the pulling power got significantly better! no more oil burning problems, have done 65K since the repair! If you plan this route, please purchase OEM head gaskets, which I didn't and regret every time I think of my first head gasket job.

 

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Nissan, when you say cylinder head job, is that what most refer to as a head gasket job?

 

[Bad Luck]

Nissan, when you say cylinder head job, is that what most refer to as a head gasket job?

A head gasket replacement is just the head gasket and doesn't include rebuilding the cylinder head or decking the engine block.

 

[1blink]

Update with additional testing results:

Pressure tested coolant system. Dropping from 17PSI to 15PSI in 10-15 minutes.

Added UV dye to coolant and drove 200 miles. No visible signs of dye anywhere under UV light.

Tested coolant for presence of exhaust gasses with engine running: No exhaust gasses detected.

Pulled and inspected upstream O2 sensor: white deposits visible on O2 sensor suggest coolant in exhaust. O2 sensor reading zero volts while driving. Swapped with good used sensor, showed correct voltage for 15 miles, before showing zero volts again.

No coolant leaking from heater core in cab.

I'd love for this to just be a valve adjustment issue.
With this set of symptoms, is there any other potential coolant loss cause I should rule out other than head gasket failure?

 

[phattyduck]

Any chance you have access to a bore scope? A clean(er) spot on a piston will also be a clue about coolant leaking into a cylinder.

-Charlie

 

[1blink]

Any chance you have access to a bore scope? A clean(er) spot on a piston will also be a clue about coolant leaking into a cylinder.

-Charlie

I don't have one. Will ask around and see if a friend does. I know coolant is going somewhere...

There isn't any coolant flowing thru the intake system on these trucks, is there?

 

[gamefreakgc]

I don't have one. Will ask around and see if a friend does. I know coolant is going somewhere...

There isn't any coolant flowing thru the intake system on these trucks, is there?

There is as there's a coolant line that goes through the bottom of the throttle body through the Idle Air Control (IAC) valve. It is not a common leak spot. What is a common leak spot is the water pump. Get under the vehicle and shine a light up behind the large crankshaft pulley and see if you see any pink/white crust. If yes you found your leak. They can also leak into the top of the engine in the valley of the "V" and you'll never find it.

Pressure test when cold is a good test for the radiator and hoses but that's about it. Most of the other leaks only occur when the engine is real hot but you can't test it when it's real hot because if you remove the cap it'll spew out boiling coolant.

To comment on the compression numbers, they aren't all that bad. Just symptoms of a tired aging engine with high mileage. A valve adjustment will help the compression and leak down test numbers substantially. Your leak down test numbers are actually pretty bad. If you heard it through the intake then you have several intake valves that are out of spec and may even be stuck open. Valve adjustments are not inherently difficult but they will test your patience more than anything else in life. You'll be tempted more than once to just chuck the valve tools out in the street before it is done.

None of this addresses the oil consumption though. 5VZ-FE's don't consume oil so something else has gone wrong. It's not going to blow up on you but your engine is wearing out. Seems to be par for the course now that these have significant years and mileage on them. Just saw another engine replacement or repair thread pop up just today..

And finally, an engine swap is perhaps the most complex job you could possibly take on. Second most would be a head gasket replacement job. For a novice mechanic I would advise against it unless you have mechanic friends willing to help. It's not like engine swapping a Honda Civic.

 

[1blink]

Thanks for the feedback, I appreciate it.
One correction: I don't think I'm burning oil, it's just puking out of the valve covers.

Have some UV dye in the coolant, can confirm no leak at the water pump. I'll pull the timing belt cover soon and get eyes on the V at the top of the engine and see if there's anything glowing in the dark there. Looks like I have maybe the remnants of an old nest in there to clear out.

Is a coolant leak at the IAC valve into the intake unlikely enough to not warrant disassembly to rule out?

I've never done a motor swap before, but I've done a clutch replacement, AC rebuild, alternator, and timing belt job on this truck.

One of my fears is going after a head gasket job, only to have lower engine trouble show up in the near future.

It's still driving ok for now, but I don't take this on long road trips if I can avoid it right now. I just bought a 2000 Tacoma with 170k on the clock, and finished getting that ready to be my daily driver. Now I can park the 4runner and deal with this, once I decide on a path.

 

[gamefreakgc]

Thanks for the feedback, I appreciate it.
One correction: I don't think I'm burning oil, it's just puking out of the valve covers.

Have some UV dye in the coolant, can confirm no leak at the water pump. I'll pull the timing belt cover soon and get eyes on the V at the top of the engine and see if there's anything glowing in the dark there. Looks like I have maybe the remnants of an old nest in there to clear out.

Is a coolant leak at the IAC valve into the intake unlikely enough to not warrant disassembly to rule out?

I've never done a motor swap before, but I've done a clutch replacement, AC rebuild, alternator, and timing belt job on this truck.

One of my fears is going after a head gasket job, only to have lower engine trouble show up in the near future.

It's still driving ok for now, but I don't take this on long road trips if I can avoid it right now. I just bought a 2000 Tacoma with 170k on the clock, and finished getting that ready to be my daily driver. Now I can park the 4runner and deal with this, once I decide on a path.

Since you used the dye, you can take a shortcut by just removing the intake tube and setting it aside. If the IAC were to be leaking coolant it would show up on the little holes at the base of the interior of the throttle body. Take a look down the throat of the throttle body while manually opening the butterfly valve and see if you can see the dye. No dye, no leak.

The more you test the more I am also leaning towards a head gasket leak but you need to be 100% sure beforehand. It is very possible that the gasket has failed but instead of leaking into the oil passage its leaking straight into the cylinder itself and burning off in small amounts. It's a lot of work to do but based on the jobs you've done before (such as the timing belt) I think you can do it. I'd still advise against the engine swap unless it's the deal of a lifetime. I've replaced one engine but pulled five engines. Pulling an engine with no intention of putting it in is not that bad just heavy, hard work with all the impossible to reach bolts. Pulling an engine with the intent to put it back in working condition is 3x the work.

All else fails, you already have a great vehicle in the Tacoma now and you can cut your losses and move on. Since it still drives well and you haven't found the leak you could honestly disclose that it is losing coolant and sell it for a decent amount. As much as I love 4Runners and fix them to keep them on the road, sometimes it isn't economical to keep them going. That's your decision to make though.

 

[Calm8809]

I've done the head gaskets on both the 3RZ and the 5VZ. If you have a mechanically inclined friend who can show you the ropes like I did it's 100% doable. A word of caution though. As Nissanh said, don't cheap out on the parts. When the 3RZ hit 301k and blew the head gasket I bought a $60 full gasket set on Amazon (I was a broke college kid trying to save a buck). Original lasted 301K, this one lasted 30K. Since then I've gone with Felpro. I'm personally a fan of their stuff and it all seems great quality to me. Not sure what the general consensus on here is about them is on here. I don't have pictures from when I did the 5VZ but I do have a small album up on here for the 3RZ from that first time around. Don't forget to get new head bolts if you do the job. They are a one time use part.

 

[19963.4lsr5]

My 97 limited had a bad intake manifold gasket and had the valley full of coolant.

My 96 SR5 had a leaking coolant hose for the throttle body heat.

For the limited I committed to rebuilding the heads. Even though I could have just done the manifold gaskets I already had my spare set of heads rebuild and had the YotaShop head replacement kit on hand.

If you pull the heads it is very worth the 200 or so dollars for the kit. It comes with everything. Valve stem seals, headbolts, knock sensor cable assembly, exhaust donuts. It’s got it all.

Those compression numbers are not that stellar in my opinion. Hopefully a valve adjustment will help.


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[1blink]

I finally had some free time today to turn a wrench. Pulled the intake tube and opened the butterfly valve: no signs of coolant or dye. There is plenty of carbon fouling and a bit of oil, related to valves out of adjustment I'm sure.

I got a decent look at the valley between the head gasket covers by pulling a few things out of the way. No sign of the coolant dye. I don't think I have coolant pooling there.

Is there anything else I should consider before settling on a head gasket leak as the diagnosis for my coolant loss?

I do have a few neighbors who used to be mechanics. Both of them are willing to offer limited help, and think it might be a mistake to go halfway on this and skip the rebuild given the age of the motor.

The new supercharger release has me thinking, maybe I'd like to get some power back. Most of my driving is at 7000+ feet elevation. Am I right in thinking that slapping a turbo on this motor without a rebuild first would be asking for trouble?

I intend to keep this rig running. It's well maintained, in great overall condition, and well modded to fit what I need from it. Starting over with a new one would cost a hell of a lot more than fixing my motor issues. I bought it 10 years ago at 150k miles for $3500, and have been tinkering with it ever since.

This will be the offroad, camping, deep snow driving rig. The taco will stay closer to stock and be the daily driver workhorse.

The advice you folks give on the forum is invaluable. I appreciate you!

 

[Asylvester]

I have a 1998 tacoma with the 5VZ motor. About two years ago at 200K miles I also experienced small coolant loss. I just keep topping it off. I figure coolant is cheap and I only need to add about every six months or so. It’s my daily driver and now I’m at 326K and continue to top off. I haven’t bothered to diagnose because it runs great. I also checked compression and numbers were not that great but really, who cares, I just drive it. I did the passenger valve cover gasket and just snugged the bolts on the driver side cover. Amazingly the truck does not burn any oil. I figure I’ll just drive it until I need a major repair. If it’s not a lot of coolant loss, just keep an eye on the overflow tank and top off when necessary. I have never done anything with the valves on mine. If you can address the oil leaking you should be fine in my opinion. The 5VZ is an amazing motor.

 

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New symptoms after a drive today. Longer drive, picked the wife up at the airport. About 80 miles in, noticed the MIL was lit. Code P0450, knock sensor bank 1. Also experienced rough idle and moderately reduced power. Possibly the leak is worsening, allowing more coolant into a cylinder?

 

[brillo_76]

New symptoms after a drive today. Longer drive, picked the wife up at the airport. About 80 miles in, noticed the MIL was lit. Code P0450, knock sensor bank 1. Also experienced rough idle and moderately reduced power. Possibly the leak is worsening, allowing more coolant into a cylinder?

Possible, however, the only way to know with testing. Need to have compression, leak down test done along with boroscope of the each cylinders.

You can mostly see head gasket leak with clean spark plugs. Bubbles in the antifreeze.

A head gasket leak will present itself. You just need to observe the signs.

Hope this helps.

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