Jump to content

HEAVY Leak from Oil Pressure Sensor?


Recommended Posts

Hello there!  First post, but same truck (1983 z24 720) HillbillyBuddha is working on smogging.  Partners in crime, I chase down the neverending electrical issues while he takes care of the heavy lifting (and knuckle busting, ow).  But now it's my turn to get down and dirty...


Since we bought this truck about 3k miles ago, it has been leaking oil heavily from the intake side, with loads of gunky blow-back build-up all the way to the rear of the undercarriage, and it only got worse over time.  It took some serious elbow grease and a full can of foaming engine cleaner to clean it up enough to realize the only apparent source was a gold thing next to the the oil filter.  IMAG1972.jpg

There is a steady drip of oil from the wires (hidden by the gunky rubber boot in this photo - I can try to take some better shots in the daylight if needed)



It also appears that a rubber boot was supposed to be covering said wires, but now doesn't seem to fit anywhere at all. I have no idea where to find a replacement boot, but NAPA has replacement sensors for $30-40.


NOTE: Oddly enough, my oil warning light AND oil pressure gauge still (seem to) function properly


So how the heck do I get that thing off?  It's a really tight fit even for my small hands/arms, but I think I felt an 8mm or so fitting at the back where the unit meets the engine. Do I need to drain the oil before I take that out?  Is there a specific torque I need to tighten the replacement to?  Any tips, tricks, or general advice is much appreciated.


Thanks in advance!

Link to comment
  • Replies 43
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

There will be a hex that you should be able to get a wrench on (underneath the "bell" of the sending unit, adjacent to the threaded segment). The measurement of 10mm sounds correct to me as far as the right size goes. You're not going to be able to torque to a specific spec. unless you're some kind of robot, so just tighten it until it feels right. If it leaks, you're too loose. If it twists off, you're too tight. Find the happy medium ;)

  • Like 1
Link to comment

You have to slip a 15mm open end down behind the sender close to the block. DO NOT FIRMLY TWIST the sender to remove or mount it, or you's bugger it up. Use a wrench to tighten it.


The rubber boot will swell from being soaked in oil. I doubt you can buy it as it's on or part of the engine harness. Best bet is a wrecking yard ... look for 4x4 or ST model 720s with the oil pressure gauge like yours. Also any '80-'90 Datsun/Nissan like the 280zx, '80 and up 200sx, Maxima that has an oil pressure gauge. You will have to cut the wires to slide it off.



Oh.... as soon as you can get rid of the Fram oil filter. They are the single worst thing you can use on your car. It screams... abuse. :lol: :lol:

Link to comment

Wow, I'm overwhelmed by your speedy and informative responses!  Thank you so much!  Money is tight, and this truck is HillbillyBuddha and my only vehicle at the moment until he finishes some work on his '66 F250, so we're being overly cautious with everything we do to it right now.  We can't afford to take it out of commission for more than an afternoon at a time.  If I had my way, I'd blow my tax return on rebuild kits and take her to pieces on the driveway for a week :hyper: heh heh



Oh.... as soon as you can get rid of the Fram oil filter. They are the single worst thing you can use on your car. It screams... abuse. :lol: :lol:


Speaking of abuse... she's who-knows-how-many thousands of miles behind on having her oil changed, so I will most likely do that at the same time.  In the box of parts I got from the po, there was a new fram oil filter.  I didn't realise that brand was so poor quality.  Considering that I intend to change the oil & filter AGAIN a month after I change it this week, how bad will it be to use the new fram for a month?



So, looks like I have my shopping list:

-better oil filter

-enough oil for a change (recommendations on brand/weight?  I was going to use whatever 10-30 was cheapest this time unless someone says otherwise)

-new oil pressure gauge (unless a used one would be fine - that'd save me $35)


I'm trying not to think about all the secondary leaks I may potentially discover once this niagra falls is plugged up. Seeing how she runs strong with 337k miles, I am desperately hoping that means the motor and tranny seals have been serviced recently.  We bought it from a guy in CA who got it from his dad in OR.  He didn't have any maintainence records for it.  Only time will tell! :thumbup:

Link to comment

For the short term fram is ok but if you can afford $6 get the WIX or NAPA Gold. As for oil yes anything will do but if keeping for the long run, next time you change it get Chevron Dello 400 or Shell Rotella T 15 W 40 oil. It's a 'light' detergent diesel oil that still has the higher zinc ZDDP levels needed to protect our 'flat tappet' motors that slowly being phased out in passenger car motor oils. If in NAPA just say you need an oil for a flat tappet motor, and they'll know.

Link to comment

Changing that D@mmed sensor had turned into a huge project.


We could only get an open ended wrench behind the sensor in one of two places. Both those places left no room to turn the wrench. We tried different angles for over two full hours. No results, not even a tenth of a turn. So while ivyracer kept trying to get a good angle, I removed the power steering pump, hoping that would give us the room we needed. When it became obvious that we still didn't have enough room to move the wrench, we removed the intake manifold. Finally, five straight hours, without a brake, we got the sensor free. Turns out the 14mm fitting on the sensor had been rounded out which just added to the difficulty of removing the dammed thing.


We've spent another 3 hours or so removing old gasket (there's got to be a better way) and we are almost done with that. But it's after midnight now and we need some sleep.


This whole ordeal had reminded me why I enjoy working on old (pre 1966) American cars. I really don't think car people design cars. Who would put a sensor in a place that requires removing an intake manifold?



Link to comment

Maybe the sensor wasn't stripped round on the corners.  There's a specific oil sender wrench made for these sensors.  It's been so long since I bought mine but they are generally in the socket selection section of O'Reilley's and marked as oil sender sockets.  The markiings on mine are "mm oilsocket" and it was made in Taiwan.  It's a "standard" six point socket with auxialliary smaller six flats to engage the corners that you thought were rounded.  This still doesn't cure the dumb placement of the sender, but if you have to remove the manifolds, it's right there waiting for the correct socket.

  • Like 1
Link to comment

You have to slip a 15mm open end down behind the sender close to the block. DO NOT FIRMLY TWIST the sender to remove or mount it, or you's bugger it up. Use a wrench to tighten it.

I went out and laid in the snow with my caliper and measured the sender on my Z24. 15mm was the closest reasonable metric size. Otherwise it was something something /64ths

  • Like 1
Link to comment

Quick question, but maybe I should start a different thread for this question?


When I put the intake manifold gasket on, what sealer should I use? If any? I usually use a gas proof sealer around the intake and silicone around coolant ports but this has both. Should I use both sealants? I've also skipped sealants altogether on intakes workout issue but I figured I'd ask here first.



Link to comment

What a beast that old sensor was to remove!!!  Even with the intake out of the way, it took all the strength and leverage I could manage just to get the first turn.  I messed up the hex so badly trying to turn my wrench in the tiny space (before we removed the intake and everything else to make enough room), I ended up using a vise-grip on the dang thing.  With enough room to get some leverage, it finally "just spun right off" like I imagine it's *supposed* to.

So, here's the old blankity blank sensor:


All the tool marks and abuse are from my frustrated attempts after trying with various wrenches for about 3 hours.  The attitude became "EFF IT, this one's broken anyway!!! Just don't mess up the threading in the block..."



This end was the sourse of the leak (it would spraaaay when the engine was under load, then just drip drip drip until she was nearly empty the rest of the time)



The hex was almost completely rounded out from multiple failed attempts to turn it in the small space.  I also believe the previous owner applied some kind of lock-tight or sealant, which made it even more difficult to turn even when I had the leverage I needed.



Here's the new one, snug as a bug.  I bought the lifetime warranty unit Autozone had for a wopping $60, but it was the only one anyone had in stock.  The threaded tip was slightly different than the one I removed.  It was a *tight* fit, and took a lot of patience to thread.  I felt like I cracking a safe :rolleyes:.  But once I caught that first thread, I was able to turn it the rest of the way with a wrench.


Now, the only thing keeping us from putting her all back together and taking a test drive is the remaining gasket that is baked onto the intake mating surfaces.  We have tried carefully scraping with razor blades (*shudder* my least favorite method for many reaons), and even let some "gasket remover" goop sit on there for a while and do nothing but drip all over a bunch of stuff I didn't want it to.  Finally had some success with a non-scratching 3m disc on a drill, but it took a whole pad just for one side.  Woke up to rain today, so it looks like this adventure is going to drag on a bit longer...

Link to comment

The oil sender location was designed for use with the L head in the 60s. The Z series wasn't a wet dream back then. Be thankful it wasn't a KA. Maybe sacrificing a wrench by putting a bend in it?


OMG I wish I had thought of that yesterday afternoon!  If I ever have to deal with this sensor again, I'm absolutely going to try that.  I also found some stubby wrenches at Harbor Freight today.  I may try those in the future.  I'm not putting any sealant on this new sensor like the po did on the one I just spent a day fighting with... I suspect that was the reason for all my woes.  It's a hard enough part to replace without having to break a cement-like seal!

Link to comment

You won't strip the block it's cast. The fitting is soft brass.


9/16" is 14.28mm  so it would clear a 14mm bolt by .24mm Maybe my measurement in the dark and snow was out or the nut is rounded on mine so forget 15mm.


It's good to know that's one thing I can't mess up on this truck, lol.



This is the box for the new sensor I've installed.  I forget which size wrench I used on it.  Either the 14mm of the 9/16 was a perfect fit.  No rounding out with whichever I used.  I found more detailed specs on it here.

Link to comment

Oh, and I ended up going with the Rotella T 15-40 and the Fram this time around.  You should have seen the cashier's face at Autozone when he realized I was putting it in my truck.  Somewhere between disgusted and horrified.  I tried to assure him that it came highly recommended on forums specific to my truck, but he wouldn't have any of it.  He insisted that it would eat up the seals in a gas motor, and that I "shouldn't trust everything I read on the internet".  I *really* wanted to remind him that he's only working retail because he couldn't get a job as an actual mechanic... (yes, I know I'm a terrible person, but at least I *didn't* say it out loud)



I drained about 3.5qt of absolute sludge.  Proof that replacing lost oil, even at a quart per week for 6 months, is not an acceptable substitute for actually changing the oil.  I'm glad I didn't cause any serious damage by putting this off for so long.  Fortunuately, I didn't find any metal shavings or other foreign substances in the sludge.


I'll drive her a month with the fresh oil and filter to work out the last of the gunk, then change it again.  She's been neglected long enough.  Time for some love!


Oh, and thanks again to everyone who has responded.  This silly little repair turned out to be quite a battle, and having so many people talk me through it helped enormously.

  • Like 1
Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...

Important Information

By using this site, you agree to our Terms of Use.