Oil and Sludge in Coolant

[Pathogenic]

Hey guys, thought I'd pick peoples brains on trying to find out what this is. Have a lot of black/ grey sludge under my radiator cap and oil floating on top of my coolant reservoir. I tried a combustion gas tester and that didn't pick up anything. Engine runs mostly ok, but gets terrible gas mileage (11 on freeway). Some oil loss but nothing absurd, and oil doesn't look very off, somewhat dark. The car isn't over heating at all except for intense mountain driving. The last 10 minutes of my drive will be a constant 4500rpm - 5000 and the engine will be fine up until I get off the freeway where it'll jump up to max, and slowly come back down. My coolant is also boiling out when this happens. It has a new radiator and water pump - thinking a bad fan clutch might be causing that. I checked compression a while ago and got about 90 psi for 1-3-5 dry and 135psi 2-4-6. Wet is was 150 1-3-5, and 190 2-4-6. I checked back when the cams were off and the timing belt was skipping teeth so I'm not sure if those are still accurate.

 

In regards to the oil, what else can cause leakage into the coolant besides head gasket? If the water pump was installed wrong, could that affect it too? The previous owner did a lot of questionable fixes on this car, so I need to recheck a lot of things he did.

 

Thanks and cheers

[R50JR]

Is that mold?

[Pathogenic]

8 hours ago, R50JR said:

Is that mold?

Haha that would be some pretty resilient mold.

[R50JR]

8 hours ago, Pathogenic said:

Haha that would be some pretty resilient mold.

Is it in the coolant reservoir? I had quite a hit of sludge in mine and rinsing it sort of helped but there is still some sludge in there. I'll probably just replace the tank. 

[Slartibartfast]

The different compression on each bank makes sense with how the timing was screwed up. Now that's fixed, I would check the ignition timing. If someone messed with that in an attempt to get it running better with the cam timing screwed up, it could be way off, which might explain both the overheating and the awful fuel economy.

 

Oil in the overflow is not a good sign. Are you sure it's oil? The inside of mine's got some rusty crap in the bottom that isn't hurting anything. If it's on top, then, yeah, that ain't good. Best case someone put something stupid in there (either trying to clog a leak or just topping it up with something that wasn't coolant), worst case... I guess a head gasket could fail between the oil port for the top end and a cooling jacket, but I don't think I've heard of a VG doing that.

 

Good that there's no exhaust in the coolant. Any butterscotch pudding under the oil cap?

 

A while back I checked out an R51 with SMOD (ATF in the coolant). The gasket on the radiator cap had swelled so much that I had a hard time putting it back on. Yours doesn't seem to have done that.

 

Did you use fresh coolant after replacing the pump? And did it look like this before?

 

Make sure the cooling system is properly bled! There's a bolt for that on the upper intake. (If you didn't bleed that after doing the rad, the resulting air pocket may have something to do with your current overheating.)

[Pathogenic]

18 hours ago, R50JR said:

Is it in the coolant reservoir? I had quite a hit of sludge in mine and rinsing it sort of helped but there is still some sludge in there. I'll probably just replace the tank. 

It is, it definitely could be leftover from another time, hard to tell if there is new material being added or not. I've replaced the coolant only once so I should do that again along with a clean/replacement of the reservoir.

[Pathogenic]

14 hours ago, Slartibartfast said:

The different compression on each bank makes sense with how the timing was screwed up. Now that's fixed, I would check the ignition timing. If someone messed with that in an attempt to get it running better with the cam timing screwed up, it could be way off, which might explain both the overheating and the awful fuel economy.

 

Oil in the overflow is not a good sign. Are you sure it's oil? The inside of mine's got some rusty crap in the bottom that isn't hurting anything. If it's on top, then, yeah, that ain't good. Best case someone put something stupid in there (either trying to clog a leak or just topping it up with something that wasn't coolant), worst case... I guess a head gasket could fail between the oil port for the top end and a cooling jacket, but I don't think I've heard of a VG doing that.

 

Good that there's no exhaust in the coolant. Any butterscotch pudding under the oil cap?

 

A while back I checked out an R51 with SMOD (ATF in the coolant). The gasket on the radiator cap had swelled so much that I had a hard time putting it back on. Yours doesn't seem to have done that.

 

Did you use fresh coolant after replacing the pump? And did it look like this before?

 

Make sure the cooling system is properly bled! There's a bolt for that on the upper intake. (If you didn't bleed that after doing the rad, the resulting air pocket may have something to do with your current overheating.)

Thanks for the reply,

 

I messed with the ignition before and after replacing the timing belt. I didn't do the water pump myself, but I did notice a screw loose when I was by there, so kinda scared by it and feel like I should redo it. With the ignition, I just looked at it again and realized I did do something weird with it 2 months ago. I noticed the rpm's were super high when I tried setting it to 15degrees BTDC or the third mark on the pulley, I just set it based on idle speed rpm to make it sound better which was quite a bit before 0 BTDC. I realize i must've masked one issue by adding another issue haha. The marks on the pulley were hand carved by yours truly since the pulley came with the marks on the opposite side, so they may be off. When I just tried setting it to the third mark, the idle goes up to 1800rpm and starts bucking on the revs. I set it to 0 or the first mark instead to keep it stable, and is sitting at 1500rpm at idle. Took it for a drive and it feels really nice driving now, a lot more power and lower rpm to maintain speed.

 

So now I think my issue could be idle related instead, I do have a code for IACV but I didn't think it would mess with the idle that much. Maybe I just need to adjust the idle speed?

 

Thanks for the bleeder screw tip, I've been trying to find it behind the intake, didn't realize it was right above the PCV. I've done that and excited to see how it does on the mountain now. Don't know if it was from this, but right after doing the bleeding I started getting loud crack/ pop sounds from both valve covers that scared the crap outta me, hoping that those were just metal doing metal things haha. It definitely is oil in the coolant, its floating and makes a rainbow sheen sometimes. The coolant below it is light green but not quite milkshake. Nothing under the oil cap, and I've been religiously checking the oil and replacing every couple hundred miles to help clean it out.

 

I'm a little worried about head gasket even though I know it doesn't happen on these engines a lot - though this one has been a bit abused. I'll be doing valve cover gaskets and an exhaust manifold when it gets a bit warmer, maybe it would be worth it to go a bit further and change the head gasket when I do that.

[Slartibartfast]

It sounds like your poor truck has a big pile of comorbidities going on here.

 

The pulley can bolt to the balancer six different ways. Sounds like the last guy put it on wrong. Fixing that will bring the marks around to where they should be. Make sure you set the timing with the engine warm.

 

The IACV's entire job is to mess with the idle. If it's stuck wide open, or some muppet adjusted it wide open to try and mask another problem, that would make it idle high. A vacuum leak elsewhere could do the same. Adjusting the IACV would be my last resort unless I had reason to believe that it had already been messed with. I would run down the troubleshooting for the IACV code in the service manual. The manual should also have instructions for adjusting the IACV properly.

 

Loud noises under the valve covers are concerning. I've heard of the cam retainer bolts coming loose and chewing stuff up. Something to check when you have the covers off, if not sooner. Might even be timing belt slap if the guy who left the water pump bolts loose was the same guy who installed the tensioner.

 

And yeah, I'd be shopping for head gaskets--or possibly a used engine.

[R50JR]

12 hours ago, Pathogenic said:

It is, it definitely could be leftover from another time, hard to tell if there is new material being added or not. I've replaced the coolant only once so I should do that again along with a clean/replacement of the reservoir.

I would flush all of the coolant with only distilled water. Drain and fill 2-3 times to get everything out, then pour 50/50 mix. Just don't leave it parked outside if the temp drops to freezing.

[Pathogenic]

On 2/18/2025 at 7:48 PM, Slartibartfast said:

The pulley can bolt to the balancer six different ways. Sounds like the last guy put it on wrong. Fixing that will bring the marks around to where they should be. Make sure you set the timing with the engine warm.

 

I'm confused where you said the pulley can mount six different ways, on this truck the pulley and the balancer are one and the same no? The truck came with this new pulley because the old one had a stripped removal bolt. I put the new one in doing the timing belt and saw that there is only one way it can fit on the crankshaft as the crankshaft has a little "tooth" on it that guides the pulley on. Perhaps I missed something? Or maybe the pulley can be taken apart?

 

On 2/18/2025 at 7:48 PM, Slartibartfast said:

The IACV's entire job is to mess with the idle. If it's stuck wide open, or some muppet adjusted it wide open to try and mask another problem, that would make it idle high. A vacuum leak elsewhere could do the same. Adjusting the IACV would be my last resort unless I had reason to believe that it had already been messed with. I would run down the troubleshooting for the IACV code in the service manual. The manual should also have instructions for adjusting the IACV properly.

Very easily could be a vacuum leak as well, I do notice a loud "whirring/ vacuum whine" near the air box but can't place where its coming from. At any rate, I'm getting 15mpg around the city now! Major improvement from before.

[Slartibartfast]

My bad, I was thinking in VG30! The pulleys on mine are bolted to the balancer. Looks like the VG33 combined the two so you can't mess it up. No idea why the marks are in the wrong place then, unless you've got the timing light on the wrong plug wire, or the rubber in the balancer has let go and allowed the pulley ring to slip.

 

Good to hear the mileage is back up, at least!

 

The noise could be a lot of things, and I don't know the R50 engine bay too well. Run it without the belts (briefly) to see if the noise goes away. If it does, check the bearings in the accessories and the idler pulley. Could be one of those singing the song of its people.

[Pathogenic]

So its been awhile but I have updates. Since I had corrected the timing more or less, the truck was acting a lot better. Getting 16.5 to 17 on the highway and 14-15 city. The same drive I would take up the mountains was a lot more manageable and could keep it going 50 at 3k rpms without overheating. Again, as I'd get off the highway it would climb a bit (3/4 gauge) but would come back down and I'd think nothing of it. I could see the coolant rising in the reservoir but it wasn't boiling over anymore. I also replaced the fan clutch at this time but didn't really notice a difference. Lasted rest of winter nicely. Come spring, and 70 degree weather, more problems haha. My coolant overflow elbow pipe burst and I replaced it surprisingly easily. I was hoping this was the cause of everything else and was pretty happy but the day after I fixed, my top radiator hose popped off and I started burning coolant on startup and overheating on steep hills. I religiously bled and burped the cooling system almost every day and was going through coolant fast. The coolant burning was most pronounced on cool humid days, but some days it would be fine. It would also act totally normal once I got up to temp and was driving around. My idle revs also fixed themself at this time, not sure how but now idling at around 700rpm.

 

My fear of head gasket is now realized and I opted to buy some crc head gasket sealer. I got home and read some reviews that were the most polar opposites 50/50 it worked or it destroyed the engine. I decided to not use that and return and buy head gaskets instead. Still not sure if it is the head gasket or the lower intake manifold gasket that was the issue, but I took the driver head off as of an hour ago, and plan on doing the other head tomorrow. I'm kinda glad to do this as I've been wanting to do the valve covers and my driver side exhaust manifold for awhile now. The driver side exhaust literally fell apart in 2 pieces when I unbolted it! Couple other things I noticed was my engine valley under the lower intake was completed submerged in oil? I think that explains my knock sensor codes as the knock sensor was actually melted where it was. I didn't notice anything particularly bad with this headgasket on the driver side but who's to say, the 4th cylinder was spotless.

 

I'm wondering if there's anything I should check for while I'm here, was thinking about performance upgrades, I've heard some people put VG30 cams in this engine but not sure. Cylinder 4 looks clean as a whistle so I'm hopeful(?) that the head gasket was leaking and I didn't waste my time taking this off. Any tips or recommendations for the stage I'm at right now? Should I clean the head and rockers with diesel?

[Pathogenic]

[Pathogenic]

[Strato_54]

I would like to chime in saying that could be calcium build up if its ever had hose water flushed through it at any point. that and heat don't usually mix well.

 

If you get it running with VG30 cams post the info. I've been wanting to do the same but don't want to pull my heads and let that JDM magic out quite yet

[Pathogenic]

13 minutes ago, Strato_54 said:

I would like to chime in saying that could be calcium build up if its ever had hose water flushed through it at any point. that and heat don't usually mix well.

 

If you get it running with VG30 cams post the info. I've been wanting to do the same but don't want to pull my heads and let that JDM magic out quite yet

It definitely has had hose water go through it, between the overflow pipe bursting and the coolant loss, i was desperate for water. Are you saying that's calcium buildup on the pistons?

 

I will make a separate post if I do the VG30 cams, for sure. Would like to get just a bit more power out of this engine, not sure if there is other stuff I'd have to replace or if it's just a drop in upgrade.

[Strato_54]

43 minutes ago, Pathogenic said:

It definitely has had hose water go through it, between the overflow pipe bursting and the coolant loss, i was desperate for water. Are you saying that's calcium buildup on the pistons?

 

I will make a separate post if I do the VG30 cams, for sure. Would like to get just a bit more power out of this engine, not sure if there is other stuff I'd have to replace or if it's just a drop in upgrade.

Just Calcium build up in the coolant. Pistons look normalish (dirty but healthy) and that knock sensor looks better than what I pulled on mine! But with all that sludge being at the top where the overflow is and you filled anyways, I would put it to being from the gross hose water that got put in to it. That's why you need to use distilled/deionized water. Someone made a point of that somewhere a few posts up.

 

From the research I did for the cams, you'll have to go with the heavier valve spring to compensate for the higher lift. More lift on a soft spring is just asking for valve float. That's it. The cam gears should be the same, and the rocker assembly. Check the valve seats though for any pitting or carbon, improper seats just loses HP. 

[Slartibartfast]

Looks like progress! Bet that manifold leak was noisy.

 

If it was blowing hoses from exhaust gas getting into the cooling system, that suggests you were right about the head gaskets. Check for cracks and warpage while it's apart.

 

The oil in the valley probably came from the valve cover gaskets.

 

1 hour ago, Strato_54 said:

From the research I did for the cams, you'll have to go with the heavier valve spring to compensate for the higher lift. More lift on a soft spring is just asking for valve float.

 

That depends on how far you go. The VG30 and VG33 service manuals have identical specs for the valve springs, so the stock springs should handle VG30 cams just fine. JWT even recommends the stock springs with their S1 cams, which if post #7 in this thread is correct, are a larger jump in lift from the VG30 cams than the VG30 cams are from the VG33 cams. JWT's S2 cams do spec harder springs.

 

And yeah, if you're pulling the heads apart anyway, that would be a great time to clean out the gunk and lap the valves. Mr. 510's VG34 thread has some info on porting if you want to give that a go.

[Pathogenic]

On 4/24/2025 at 12:38 AM, Slartibartfast said:

That depends on how far you go. The VG30 and VG33 service manuals have identical specs for the valve springs, so the stock springs should handle VG30 cams just fine. JWT even recommends the stock springs with their S1 cams, which if post #7 in this thread is correct, are a larger jump in lift from the VG30 cams than the VG30 cams are from the VG33 cams. JWT's S2 cams do spec harder springs.

 

And yeah, if you're pulling the heads apart anyway, that would be a great time to clean out the gunk and lap the valves. Mr. 510's VG34 thread has some info on porting if you want to give that a go.

Got the passenger head off finally, was battling the lower middle exhaust bolt. The gasket on this side looked a little scuffed but the leak wasn't obvious; however, my head bolt on the back left was completely rusted so maybe the leak was happening around there. Cylinder 3 looked cleaner than cylinder 4 did. Would you guys recommend I get the heads resurfaced? I don't have a mechanics straight edge but I got them pretty clean and they looks alright to me.

 

Also just picked up the cams from a 93 vg30e and was wondering about them. I put them side by side with the old ones and did not notice any difference in their sizes, would it be noticeable? They also have the same "4" imprint on them.

[Slartibartfast]

Clean is a good start, but given their history, you should at least put a straightedge on them.

 

The flatness spec (from EM-24 in the '97 manual) is 0.01mm (0.004"). Put a straightedge across the head (corner to corner, diagonal and parallel) and see if you can get a four thou feeler gauge in between anywhere. If the feeler fits, resurface or replace the head. Don't cut more than 0.02mm (0.008") off the head. If the cam doesn't spin freely in the head, because the head is warped to where the cam bearings don't line up anymore, replace the head.

 

The difference in lobe height between the VG30 and VG33 is only around 0.3mm on the intake, 0.6mm on the exhaust. You're gonna need calipers to see that. Measure from the tip to the base circle on the far side (the full height of the egg, if that makes sense). The '95 manual says the VG30 lobes (intake and exhaust) should be 39.537 to 39.727mm. The '97 manual says the VG33 lobes should be 39.242 to 39.432 on the intake, 38.943 to 39.133 on the exhaust.

[Pathogenic]

Thanks for that, I'll check the flatness.

 

Any thoughts on the Z31 w series cams? Just saw I might have access to those after getting home haha. They have these specs and shooould fit: 

Grind Number:	Z31 All
Intake Duration (gross):	252
Exhaust Duration (gross):	252
Intake Duration (.050”):	194
Exhaust Duration (.050”):	194
Intake Valve Lift*:	.393"
Exhaust Valve Lift*:	.393"
Lobe Separation:	111
Intake Valve Lash:	.000"
Exhaust Valve Lash:	.000"
RPM Range:	1000-5000

[Slartibartfast]

Looks like they've got the same lift as the VG30 cams, but a little more duration. Mr. 510 called them the best stock cams from the US market (or words to that effect) in his VG34 thread, so if a set happens to fall into your lap, I'd call that a win!

 

This chart of stock cam specs shows the Z31 cams second only to the Euro cams, which again have the same lift, but a little more duration. Looks like the Euro cams moved the power band up just a little (traded a little low-end for a little high-end?), but nothing crazy.

[adamzan]

On 2/20/2025 at 9:47 PM, Slartibartfast said:

My bad, I was thinking in VG30! The pulleys on mine are bolted to the balancer. Looks like the VG33 combined the two so you can't mess it up. No idea why the marks are in the wrong place then, unless you've got the timing light on the wrong plug wire, or the rubber in the balancer has let go and allowed the pulley ring to slip.

You probably know this by now, but the VG33 pulley/balancer is put together with some rubber isolator in between. They were known to go bad back in the day, my dad had his replaced 2x under warranty by nissan on his 2000 pathfinder. It would slip, make noises, and cause the timing readings to be incorrect.

[Pathogenic]

So I finished replacing the head gasket, and so far it seems to be good! My straight edge showed I had a 0.008" gap on the heads which is twice the spec tolerance. Had them cleaned and resurfaced. I also checked the seal on my valves and realized that one was leaking. Did my best to lap it but to no avail. Had my machinist do a 3 angle grind on it and he also bumped the seat. I put some z31 cams pulled out of a 1987 300zx into it which was good because I realized the old cams were scored on some of the lobes. I also pulled apart all my lifters and cleaned them as they were all stuck. I also had to tap a bigger hole on my coolant top off hole on the plenum as it was stripped and leaking. I also moved the knock sensor to the top of the plenum, but I might move it back as I think I need the ignition adjustments that it would help with.

 

So to finish the object of the initial post, it was my head gasket that caused the issue.

 

Now the only issue i see is my ignition timing, the closest I can set it to 15BTDC is 20BTDC, i messed with moving the splines on the distributor for like an hour but that's the closest I can get it. The power output is meh, seems pretty poor on the low end but pretty good on mid-high end. I was hoping with the new cams to see some better results but I think the timing has something to do with it. It feels strong only at 3k plus rpm. and very weak under that. The truck is a LOT quieter with the exhaust manifold replaced and the lifters cleaned. I'm trying to think of a way to get the timing right, either something is off, or I was thing of getting a bolt that's thinner near the head so the distributor has more room to travel. But at the very least, the coolant is not pressurizing out of the overflow anymore, and there is no coolant loss i can see.

[Slartibartfast]

Good work getting it back together. Sounds like the distributor is off a tooth. Or is that what you meant by moving the splines? Make sure you're setting it with the engine warmed up. Also check that the balancer hasn't slipped, as Adamzan noted above. Hopefully clearing up the timing wakes it up!

 

On 5/19/2025 at 6:54 PM, Pathogenic said:

I also moved the knock sensor to the top of the plenum, but I might move it back as I think I need the ignition adjustments that it would help with.

 

EC-23 of the '99 manual says that the knock sensor is not used to tune the engine. It's just to tell the computer if something goes wrong. I relo'd the sensor on mine to the back of the driver's side head. Haven't had any issues with it. I was glad I did it when the sensor failed and I didn't have to pull the intake to swap it out! But I imagine it would struggle to pick up the sound of knocking from the passenger's side, if something did go wrong.