My 1990 300zx Twin Turbo build by megaDan

10 minute(s) of a 731 minute read

Everything went mostly to plan this weekend. Friday night I got the block almost ready to drop in. I was stymied at the last second when installing the upper intake manifold only to find the last of the 8 mounting locations was stripped. All 7 others I've already time-serted, so that was my first task Saturday morning.

I was in the garage by 5:30AM, and when my time was up at 7:30 I had the engine in place ready for the transmission. Not much to say about it, everything was smooth and uneventful. Kind of surprising for a solo engine replacement. I didn't get much more time Saturday aside from sliding the transmission under the car and having it ready for Sunday morning.

Sunday was a bit more challenging as it took a little while to figure out how to get the transmission up 6 inches onto the transmission jack, all while under the car. It won't clear the front cross member, and it wont clear the tunnel going backwards. I got creative with the tools at my disposal and rocked it up onto a rubber block on one side, and then on the other, which gave me enough leverage to lift the transmission with one arm, so I could position the jack with the other. From then on it was smooth sailing again. I spent a good chunk of the day in the garage and managed to have everything in place aside from the radiator and wiring. I knocked out those tasks over 90 minutes each of the last two nights.

The plan for tonight is to install the battery, add coolant, power steering fluid, 5 qts of Rotella T6 (vs M1 10w40 I've used forever) and run it for approximately 5 minutes. I'm going to do an oil change to flush out any potential coolant mixed oil froth that might be left in the bottom half.

If that goes well and it dries out today....test drive?

No promises, but this might be the last before and after:

Approximately 18 months ago

Approximately 10 hours ago.

I'm really pleased with how it looks and how it turned out, but despite all the paint prep I did, and the 9 coats (3 primer, 3 color, 3 clear) the paint is still thin and fragile and I don't expect it to last long. I'm pretty bummed about that. Powdercoat if there is a next time.

So....its been a bit of a rollercoster. Please stick around because I need some input at the end....Before adding any fluids, pressurized the cooling system before filling to verify there were no major issues. Then I did a boost leak test and discovered leaks at both my VTC solenoids at the back of the intake valve covers. This added a decent delay as I had to remove the intake manifold and both valve covers, apply RTV to the top half of the solenoid (I haven't done this in the past), wait 24h for cure, and reassemble.

After a little more adjusting I managed to get the intake system airtight. I added a 50/50 mix of coolant and distilled water, oil, and after a few stumbles got her going.....and found a fuel leak at the return side of the rail. Since installation 9 years ago I've never dealt with any fuel leak issues, but I must have bumped it once or the way I had it resting for a few months didn't agree with the braided line > AN connection. I disassembled the fittings, installed the rail to a spare intake manifold, pressurized the system, let it sit for an hour or so, and reinstalled it for real after confirming I corrected the leak.

Thank god for spare parts. Rudimentary test bench.

Fired her up again, and discovered a slight miss. I re-used the plugs I had in before as they were all in great condition; so I swapped out the plug in cylinder 5 only (the location of the blown HG) and everything was butter smooth. Yay! I let it run for 3 minutes or so while continuing to add coolant.

I shut it off, drained the oil...or what should have been oil, and was met with more opaque tan fluid. My heart sank pretty much immediately and my brain went to worst case scenario. Headgasket didn't seal. Something major is wrong. Need to pull the engine and start over or find a junkyard. Bad times.

I filled it up with more oil, let it run a little longer while I kept checking the oil fill port on the valve cover for what I was hoping would be oil. While running it still seemed to be more opaque tan than clear oil.

Since then:
-Dipstick looks super clean. Clear, not frothy. Wiping it on a white towel shows exactly what brand new oil would look like.
-Valve cover shows mostly clear residual oil in the valve cover, but when running it takes on an opaque quality.
-Leakdown test on all 6 cylinders was between 18% and 22%; however I'm not sure I trust my US GENERAL tester as the regulator pressure to zero the unit out is only 14PSI. I ended up setting my compressor regulator to 60psi and bypassed the gage and fed air straight to the cylinder. Very similar results, but with much less resolution on the data as I had to take readings from the compressor itself. Regulator pressure was close to 60, and it looked like it might have dropped to 53PSI, which is ~13%. No sound or bubbles from the radiator/exhaust/intake, everything was through the crankcase as it should be.

I have NOT done a compression test yet. My plan is to buy another 10qts of oil on the way home, do another flush and see if the color of the oil has improved. If it has, I guess I'll stop panicing. If it has not, I'll do a compression test. I'll probably do a compression test either way because I'd like to establish a baseline for future reference.

My question is....am I worked up for nothing? I didn't remove the pan during my rebuild...now I wish I had. Should it take a few flushes to get all the residual milkshake out? Water is denser than oil, is it possible there's still a layer at the bottom of the oilpan? I have hope after encouraging leakdown results, but the condition of the oil is still incredibly concerning. Do I get it up to temperature and add seafoam? Take a few gentle drives to heatcycle the engine and boil off any residual oil? That's my last resort as I'd prefer to run the engine as little as possible until I can confirm the oil is mostly water-free.

Ugh.

Sort of? I drained the oil and coolant, pulled the engine. Removed the heads, but never dropped the oil pan. Reassembled, reinstalled, and drained the pan again prior to adding new oil. I was surprised by the amount that came out the 2nd time.

Also, to answer your question, no silly VW-like coolant to oil coolers. The Z32 (TT only I believe) has a dedicated oil cooler which is fed from the oil filter tree and returns directly to the oil pan. The place area the two get close aside from the headgasket is the turbos as they are watercooled.

Anyway, I very much appreciate the input and I think the dye idea from Stevo12 is brilliant. That would never have occurred to me. Thankfully it also looks like I won't need to worry about it for the time being. First thing I did when I got home was drain the oil (2nd time since rebuild) and it came out looking much more like oil. Still slightly cloudy, but very much improved. I fired it up and it sounded better than it has in a long time. Very smooth, very quiet.

After some clutch bleeding shenanigans, I was finally able to engage reverse and get it out of the garage. Test drive was mostly uneventful....but also brilliant. The engine felt 'tight' and ready to go. I know this is a poor description, but its the most accurate adjective I can come up with.

There are just a few items to address:
-The wideband was pegged lean at idle, but the numbers jumped around with medium throttle. Perhaps fouled from coolant when the headgasket failed? I've got a replacement sensor on order. It's running so smooth I just don't believe it's a vacuum leak, but I'll verify that tonight.
-Power steering was also a little too firm and jittery, it seems I need to do some more bleeding there too.
-I still seem to be dealing with overflow issues, as its not pulling coolant back. Very much a "D'OH" with this issue.

I didn't give it ANY power, never saw boost. I'll continue to do 15-20 minute test drives to flush out the system and burn off any residual moisture, and change the oil after 200 miles or so before it sees boost. But by then it will also probably see the other side of the garage and be parked for winter.

12-15-2020

A new WB02 solved the issue. Apparently there were a few factors at play. I didn't realize coolant would foul an 02 sensor so quickly, but this one was on the bank with the blown HG, so that makes sense. The sensor was white when I removed it. Secondly, that sensor was already 5 years old; I thought it was 2 years, max. The first WB02 I used died after about 5 years, so it was probably near end of life anyway. I purchased a new Bosch sensor, did a calibration, and everything looks stellar. I'm still running a single WB02, it's probably time to investigate a dual sensor setup to cover the second bank.

Regarding the other issues I brought up in my last post, I believe the power steering intermittency is due to my speed sensor. I noticed during a drive on Sunday that my odometer had briefly stopped working, and this speed sensor also controls the speed sensitive power steering. I'll need to determine the diagnostic procedure for this, it was only out for about 10 minutes or so; I haven't had an issue since.

Coolant overflow issues are resolved! I'm not sure what was wrong with my generic overflow, but it clearly wasn't doing the job. My nose mounted gatorade bottle (temporary solution while I troubleshoot) has functioned perfectly after a few drive cycles. My plan is to pick up an appropriately sized OEM reservoir from another make/model and mount it in an easy to monitor location so I can keep tabs on it. Having it inside the bumper is great for space, but terrible for visibility.

I gave it a final oil change last night after a good 40 mile drive Sunday. The oil came out very clean and I'm no longer concerned about contamination. I'll be heading into work late this morning, and the plan is to stretch its legs a few times and see what it feels like.