82 Datsun Caravan (Z20)

[richURVAN]

Hey folks,

 

I'm looking at buying the above but it needs a new head gasket . . . so have been considering my options . . . 

 

Don't want to go too deep down a rabbit hole with this, preferably just getting it on the road for part of Summer, but I figured if I'm taking the head off I may as well make some improvements. Looking for any recommendations?

 

I have read that the L-series heads are the go for better performance or will this be negligible on a stock standard Z20 motor? I can get a replacement Z20 head for about 900 bucks and I'm not sure how available old Nissan parts are here in Australia so may just run with that if need be. 

 

Obviously I don't know the circumstances around the head gasket going or what the condition of the engine/head is until I take it off, any tips what I should look out for? Will be my first head gasket job.

 

Ta,

Rich 

 

[datzenmike]

First... do NOT touch the cam sprocket till you know how to block the timing chain tensioner from falling out. This is important and will save you half a days work to fix your mistake.

 

If the gasket is the problem, it's only $30 Canadian for a new one. Why spend $900 on another head? Gasket is cheaper.

 

How do you know the head gasket is bad??? The present owner may just think it's the gasket when it really something much more serious. Like a broken piston or burnt exhaust valve.

 

How long has it been sitting with this 'blown gasket'???? if long enough, chances are that water has run down into the cylinder and rusted it.

 

 

Negative on the L head. That's way too involved to do.

[richURVAN]

I was hoping you would chime in buddy I've been trawling the net and your posts come up in just about every thread on nissan/datsun engine stuff! Legend! 

 

That vehicle actually sold before my eyes bit of a shame but maybe a blessing in disguise! 

 

I went with a 91 Nissan Urvan in the end with a tired Z24 engine. Still runs but get's hot in traffic / heat of the day. Thinking the fan clutch has seized based on my research, apparently aftermarket types are all junk so trying to get a Genuine Nissan one in Australia (proving difficult).

 

So you reckon the L series head is too much work for a novice YouTube mechanic? I've got an awesome tutorial on changing the timing chain. Or perhaps I just keep it stock throw on a better induction kit and exhaust. 

[datzenmike]

Here the Z24i powered Vanette ('87, '88 and about half way through the '89 model year before it was cancelled) was eventually recalled. Nissan bought them back and crushed them all. Some few owners kept theirs. The reason? Un-fixable overheating and occasional fires because the van was designed for a smaller engine but to keep up with traffic in the US the larger Z24i was installed and there were cooling problems.

 

If the clutch fan seized it would spin faster as it would be locked to pulley speed and not be slipping at higher speeds. More likely the clutch silicon oil has leaked out and it's slipping too much. Spin the plastic blade with your finger. It should offer firm resistance but turn smoothly. You should not be able to spin it fast enough to keep spinning and should immediately stop once you take your fingers off it. The clutch fan is integral with the water pump and has to be replaced as a unit.

 

The Z24 and Z24i are notorious for blowing head gaskets every 100,000 miles. The best way to avoid this is to re-torque the head bolts once a year. This assures an even clamping force on the head gasket. The procedure is to do this on a cold engine. Loosen only one bolt at a time and tighten to 60 ft. lbs. Only then move to the next bolt. You can do in any order you like but only one bolt loose at a time. 

[richURVAN]

Dam I nearly bought a Vanette as well Z24 not sure if it was injection or not.

 

That's awesome info buddy, and makes sense because the cutch definitely engaged at some point on the test run (as it quietened right down). I'll check it again when I pick up the Van on Sunday by hand. I figured I'd do a complete coolant system overhaul starting with the water pump and fan clutch but I'm struggling to find anything Genuine Nissan or decent in Australia so far. I read a sticky on another forum re the 280z water pump and then you fit electrical fans or a separate fan clutch to stay mechanical (my preference) but I'm unsure if that was using the 280z fan clutch or KA fan clutch along with the KA pulley and original Z24 belt. 

 

I also figured if it was a water pump or rad issue it would overheat pretty darn quickly, this motor just get's hot after while on hot days or over 100k's. Head or gasket could also be the issue I guess more investigation will tell. This is the info from the seller;

 

"Its not to bad in traffic but yeah if its a hot day its not great and on the freeway it seems to cool down if you go from 100ks to 80ks but only worry about that if it's getting hot"

 

🤷‍♂️

[datzenmike]

The fan should slip and remain at about 1,800 RPMs but if it senses the radiator air is getting too hot it will release more clutch fluid internally and can spin up to 2,200 RPMs so you may hear a change in sound.

 

Does the radiator need topping up often?

[richURVAN]

No rad doesn't need topping up often the seller said?

 

Aha so if it's slipping too much much it may not be disengaging when it needs to (radiator air getting too hot). I just instantly suspected the fan clutch because it seemed like it was blowing way too fast / sounding like a jet engine when I fired it up and idling / slow speeds, and didn't sound like previous z24's I'd test drove. 

[richURVAN]

*engaging 

[datzenmike]

If it sounds like  jet taking off then probably seized. But then it would move way too much air and unlikely to over heat

[Stoffregen Motorsports]

There are two different types of fan clutches, thermal and non-thermal.  A thermal clutch will grab more as the temp rises, while a non thermal will grab at low RPMs and loosen up as the revs climb.

 

Datsun/Nissan probably did not use the non thermal clutch.

[datzenmike]

Clutch is the term for 'fluid coupling'.

 

Torque coupled clutch fans limits fan speeds to 2,500 RPM. Engine can continue to rev higher but fan cannot.

 

Temp coupled clutch fans in the OFF position, limits fan speeds to 1,600 when cold or not needing extra cooling. When extra cooling is required, a valve is opened allowing more clutch fluid in, increasing the fluid coupling and allowing the fan to speed up to 2,150 RPMs

 

Air condition vehicles used the temperature controlled clutch fans. At least the Datsun vehicles but it's been my experience that roughly '80 and up, when displacements rose above 2 liters, the temperature controlled clutch fans were more prevalent on non air conditioned vehicles. All the Z24 720s I've seen (without AC) had the thermal coupled fans.

 

 

..................................... Torque coupled............................................................................................................... Temperature coupled.............................................

 

[richURVAN]

Yeah should be a thermal coupled fan right. So I picked up the Van last night and drive it home and here's what I noticed . . . 

 

The fan is really loud on pull away 1st, 2nd gear . . . then it quietens down. Every time I stopped at a set of traffic lights the temp gauge started climbing up to half way and just past in some instances, and no sign of the fan shifting to a higher speed?? Along the highway though the temp gauge stayed about a 1/3 of the way. When I spin the fan by hand (engine off cooled down) it stops as soon as my finger leaves the blade almost. 

 

I've checked the oil and coolant for any signs of head gasket damage and both look ok. Thinking if it's not the fan perhaps it's the thermostat. 

 

[datzenmike]

Correct temperature readings is about 1/2 way in the 'run range' and just a hair above that. So if the thermostat is working properly it should stay there and not go lower, you see, the thermostat sets the lowest engine temperature not the highest. 

[richURVAN]

6 minutes ago, datzenmike said:

Correct temperature readings is about 1/2 way in the 'run range' and just a hair above that. So if the thermostat is working properly it should stay there and not go lower, you see, the thermostat sets the lowest engine temperature not the highest. 

 

The temp gauge def wasn't constant unless on the highway, it was fluctuating above and below the half way point 🤷‍♂️ So sounds like the thermostat could be faulty as well (if there is even one in there). . . 

 

So what sets the highest engine temp the thermo mechanism in the fan clutch? Which should engage the fan at higher rpm's once highest temp is reached? 

 

 

[datzenmike]

Engine temperature...

The thermostat should be maybe 180F. This is the temperature where it begins to open. so you can see that if the engine should cool down the thermostat will close at 180F and will remain there and not go lower. When open the radiator should easily be able to cool the engine of all the heat it makes and then some even out in the desert in the summer it should remain at about 180F. If your gauge goes well below 1/2 then the thermostat is not closing fully.

 

A needle width of up and down would be ok, but generally it should be and remain very close to 1/2. This is not the end of the world and the engine will run ok if at the low end of the temperature range but it was designed to run it's best at 180F. Emissions, power, mileage, efficiency, engine life are best at this temperature.

 

Did you spin the fan blade with you hand? How was it??? 

[richURVAN]

1 hour ago, datzenmike said:

Engine temperature...

The thermostat should be maybe 180F. This is the temperature where it begins to open. so you can see that if the engine should cool down the thermostat will close at 180F and will remain there and not go lower. When open the radiator should easily be able to cool the engine of all the heat it makes and then some even out in the desert in the summer it should remain at about 180F. If your gauge goes well below 1/2 then the thermostat is not closing fully.

 

A needle width of up and down would be ok, but generally it should be and remain very close to 1/2. This is not the end of the world and the engine will run ok if at the low end of the temperature range but it was designed to run it's best at 180F. Emissions, power, mileage, efficiency, engine life are best at this temperature.

 

Did you spin the fan blade with you hand? How was it??? 

 

Yeah span it when engine off and cooled down and it stops as soon as my finger tip leaves the blade 👍🏼

 

I just had a better look around the engine bay and I think the water pump is not original as it appears to have a separate pump / pulley / clutch assembly. Correct me if I'm wrong (how do I upload pics?)? Then I bet a poor quality fan clutch was fitted, I've heard there are fan clutch's which look like thermal but they've actually got no insides i.e. NPW brand. 

 

 

[datzenmike]

1 hour ago, richURVAN said:

Yeah span it when engine off and cooled down and it stops as soon as my finger tip leaves the blade 👍🏼

 

 

 

Yeah that's totally fine. Some were actually two piece, I've just never seen them.

[richURVAN]

17 minutes ago, datzenmike said:

 

Yeah that's totally fine. Some were actually two piece, I've just never seen them.

 

Yet it doesn't seem to speed up when the radiator heats up and temp gauge climbs above halfway point 🤷‍♂️

 

Any other tests I could run? If I were to replace just not sure which to order I guess it's a matter of taking it off and hope there is a part number on it or i could measure it up . . . 

[datzenmike]

It may not. It speeds up when it senses an over temperature of the air passing by it. You said it only gets to 1/2 and I say 1/2 is about where it should read on the gauge. So not at all close to over heating. I'd say everything is normal. How low does it read below the 1/2 once warmed up???

[richURVAN]

16 minutes ago, datzenmike said:

It may not. It speeds up when it senses an over temperature of the air passing by it. You said it only gets to 1/2 and I say 1/2 is about where it should read on the gauge. So not at all close to over heating. I'd say everything is normal. How low does it read below the 1/2 once warmed up???

 

Nah it goes above half if sitting at traffic lights and the previous owner said he's seen it almost hit the top of the gauge, definitely not normal. I'll go and run it and take pics . . . 

[richURVAN]

1 hour ago, richURVAN said:

 

Nah it goes above half if sitting at traffic lights and the previous owner said he's seen it almost hit the top of the gauge, definitely not normal. I'll go and run it and take pics . . . 

 

Just took it for a spin and I guess the needle sits around 1/3 - just under half the way once warmed up but it's not very constant i.e. drops to a 1/3 on highway then I've seen it above half - 2/3 sitting at the lights (and I know from the previous owner it would reach the top). I drove with the passenger seat (bonnet) up and the fan seems pretty noisy/constant even when on the highway. 

 

I also tried to stop the fan with a folded piece of paper once warmed up and it shredded it so it's def not free wheeling. Seized more likely - so the overheating must be something else, back to the drawing board! 

[datzenmike]

I would spend about $10 Canadian on a new thermostat. W/E that is in Australian currency, get a good one not a $1.99 special. It should be more consistent than that and be steady at just barely over 1/2. My guess is it's stuck partly open making it slow to warm up, runs hot at low speeds (not open enough) and runs a bit cool at high speeds. (not closed enough)

 

 

My 710 sedan was slow to warm up. It would reach 1/2 if driven, so it did open properly, but would drop below if idled. As you can see here the thermostat couldn't close properly. I've have never seen a thermostat with a rubber seal before. May have been the original as the muffler was and the mileage was about 20k miles. All the hoses were original too.

[richURVAN]

Thanks buddy I'll give that a go and may as well change the pump since I'll be draining the coolant, and I definitely want to change the fan clutch as the fan is way too noisy! Are there any stickies for such an operation you know of?

 

Ta

[datzenmike]

Don't fix what isn't broken*. Only reason to change the pump is if the bearing is noisy or the seal is gone and it's leaking. On the underside if you look hard is a small hole. If the seal fails it allow coolant to drain rather than contaminate the bearing and causing seisure. It's assumed the owner will find the obvious leak and replace before this happens.

 

 

*Original parts are superior to after market ones. Preserve and keep them as long as possible.

[richURVAN]

Yeah I totally agree with you on that! Ok I'll inspect it when I change the fan clutch . . . 

 

I'm assuming I've got to drain the fluid to change the Thermostat though right?