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Z24 engine best way to disable the fuel for compression test??


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I'll try to take a good picture tomorrow. If that was for bleeding air wouldn't it be as high as possible? I think it's meant for something not used and is just a plug.

 

Ah!!! Look at the top right. That's your temperature sender. Ours was where that plug on yours is. I guess they moved it after '86.

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19 minutes ago, datzenmike said:

I'll try to take a good picture tomorrow. If that was for bleeding air wouldn't it be as high as possible? I think it's meant for something not used and is just a plug.

 

Ah!!! Look at the top right. That's your temperature sender. Ours was where that plug on yours is. I guess they moved it after '86.

 

Aha got ya. Yeah that's what I thought why is it lower down, in the end I used the temp sender screw to bleed it whilst i pressure filled it with the hose as it was higher and easier access. 

 

No luck unfortunately although it didn't force any water into the reservoir, I just watched as the temp gauge reached 3/4 and then I switched it off and you could feel/hear the water boiling in the hoses and engine.

 

I'm close to throwing in the towel bro i don't know what else to do.

 

The only things I haven't replaced are all the hoses, water pump and oil pump (I've heard that can cause overheating as well). 

 

Maybe I'll drop it off to the Mechanic and let them run all their pressure tests with the compressor see if they can spot something. 

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Is there a hose connection that sits higher than anything else? If so, disconnect that hose while filling the system, then plug that hose in once it starts to flow over.

 

Re- the funnel. Let it run, for an hour if need be. If there is a large bubble in the system, cycling the thermostat and time are the only way it may find its way out. And once you're done with the funnel, shut the truck off, top off the funnel and walk away. Come back in the morning after it has sucked down whatever coolant it's going to and then put the rad cap back on.

 

Give it one more shot, just as I illustrated above, with no removal of funnel and plenty of time.

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If boiling it would be building pressure and the only way out is the overflow. If no overflow, no boiling. Not only that but the gauge should be higher reading.

 

Can't see how air would be trapped except when initially filling the cooling system. As soon as the thermostat opens any air would be released and collect in the radiator top, would be noticed and topped up. The coolant outlet from the head to the intake and the thermostat IS the highest point on the head.

 

These are Z24 top and Z20 beneath it. They are also upside down. The outlet is the opening just to the front of the #1 intake port. Nowhere for air to be trapped while the thermostat is open. In addition the water pump is pressurizing the block and head pushing towards the thermostat.

 

MCUaJNk.jpg

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Right, but there may be other higher spots in the system, like a heater control valve or the heater core or even just a looped hose.

 

I went through this last year with the LS swapped Land Cruisers I build. The heater valve is higher than any other spot in the system and only by burping the system with the hose off and then filling with the use of the funnel, basically as I described it above, is the only way to get all the air out of the system. I even considered running a header tank, mounted higher in the engine bay, but I figured out another solution. Ultimately, the air trapped in the system caused the water pump to cavitate at certain RPMs.

 

So back to this one. I understand the configuration of the engine, but are there any high spots in the system that are higher than the engine?

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While not familiar with the Vanette as Nissan instituted a buy back offer and destroyed them. However there are lots of other Z series engines in cars and trucks and they were not known for trapped air being a problem and besides the engine is tilted up at the front and the water pump would push any air out past the thermostat and into the rad. Why would you design something that traps air in the first place?

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Why is a question I don't give much regard to. If it is, then it is, and then I find a solution. If there is a high spot, then there may be a problem. Toyota designed a high spot in the system, and other cars have this issue too. Neither you or I know anything about Vanettes, so it wouldn't hurt to at least pursue the line of thought.

 

Or we could think about why...

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Trapped air isn't going to bubble or if it is then it's getting out. Keep driving and it will fix itself. Bubbles are almost always a blown head gasket.

 

Still need to know if system pressurizes when running but not warmed up yet, and does it expel coolant into the over flow? Another sign that compression is escaping into the cooling system.

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Cavitation is just low pressure behind an impeller that causes the water to 'boil' just like water boils at a lower air pressure (and thus a lower temperature) on a mountain. The bubbles (almost a vacuum) quickly collapse when pressure returns. They do it so quickly at high speeds that they producing a shock wave. Anything near cavitation will be subject to erosion damage.

 

 

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Thanks for the input guys . . . 

 

The heater core is the highest point in the system hence I've bypassed that for now, as well as the thermostat in case it's faulty.

 

Yesterday I pressure filled the system with the garden hose (T'd into the heater hoses) whilst bleeding air out both the rad cap (for any air trapped in the rad) and the temp sender screw (for any air trapped in the intake/block). 

 

I'm pretty sure i got all the air out. Then I ran it up to operating temp and the temp gauge went way high 3/4's and would of kept going had I not switched it off, and i could hear/feel the water boiling inside. 

 

I'm starting to think it's the water pump and I don't know why I overlooked this in the past. The pump is working poorly/intermittently hence the water is getting held up (levels rising up in the funnel) and not circulating properly (if at all). 

 

But I'm pretty sure the gas that is coming out is steam and not exhaust now.  

 

I will try one more time this morning and get a video of the funnel I'm just weary to keep boiling the water in the system and essentially overheating the engine when I just spent a ton of money on the head. 

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1 hour ago, datzenmike said:

Trapped air isn't going to bubble or if it is then it's getting out. Keep driving and it will fix itself. Bubbles are almost always a blown head gasket.

 

Still need to know if system pressurizes when running but not warmed up yet, and does it expel coolant into the over flow? Another sign that compression is escaping into the cooling system.

 

Will test this again this morning. Did you see the picture of my overflow tank and cap with the lengths of hoses? I'm wondering if that is all correct? 

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The overflow isn't very technical.I've run a hose into a coke bottle. As long as the hose is submerged it will work fine.

 

Getting down to the nitty gritty so sure, pull the pump off. The pulley spins an impeller. If loose on the shaft or vanes damaged??? Unlikely they seldom fail usually the bearing gets noisy or the seal leaks. if it looks ok then it is.

 

eJ8O8IA.jpg

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14 minutes ago, datzenmike said:

The overflow isn't very technical.I've run a hose into a coke bottle. As long as the hose is submerged it will work fine.

 

Getting down to the nitty gritty so sure, pull the pump off. The pulley spins an impeller. If loose on the shaft or vanes damaged??? Unlikely they seldom fail usually the bearing gets noisy or the seal leaks. if it looks ok then it is.

 

eJ8O8IA.jpg

 

Well that's the thing the hose actually isn't submerged! I'll fit a new longer hose so it almost touches the bottom of the tank. 

 

And what about the length of the hose fitted to the cap on the outside? Doesn't matter?

 

Re the water pump, given the state of the inside of the rad I'm pretty confident the pump impeller will be rusted/corroded. PROBLEM is finding a decent replacement here in Oz . . . it's got a separate fan clutch so not original, so based on prior reading I'm looking for a pump off a 240Z or 260Z, 280Z, 280ZX? I also wonder about the KA24 pump fitting??

 

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Hose should be close to bottom of container and container 1/2 filled.

 

Take it off first. Inspection will most likely tell you it's fine. Or not. Then you'll know.

 

KA water pumps are different. All L and Z series will interchange but Z series are larger impeller and deeper pump cavity...

 

L series

4KizyLY.jpg

 

Z series

eJ8O8IA.jpg

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HOLY SHIT! In all my wrenching I have never seen that! Well I believe you found the problem! I wouldn't feel bad about changing the head gasket and checking things over, just means you know how everything looks and can depend on a fresh good gasket job!

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I hadn't really thought about it before now also, but if you remove your radiator cap and start the engine up you can see some turbulence or a small 'wake' in the radiator. I am guessing yours was just flat and bubbling do to no current! 

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  • 3 weeks later...

Hey Folks apologies for the radio silence I'm still elated after pulling off that water pump! Massive thanks to the OG's on this thread especially Mike 'The King' and Stoffregen Motorsport I literally would of given up without their help!

 

I drove 800km in the Van and the temp gauge stays under a 1/3 almost too cold?? ha 

 

The only thing I need to get sorted on the engine now is the fan clutch, as it's making a hell of a racket, it only knows one speed, MAX.

 

It's not engaging/disengaging the fan even at motorway speeds where the air flow is obv more than sufficient to cool the engine. 

 

I've heard the aftermarket fan clutch's are junk although I thought the Dayco one I bought would of been ok but nah.

 

I wonder about getting a Genuine Nissan part from overseas, does anyone know the part number for the fan clutch I'm after? It's separate from the water pump. 

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On 4/9/2022 at 2:54 AM, Stoffregen Motorsports said:

Glad you figured it out. Sometimes it takes a village...

 

Faulty fan clutch can be worrisome. I've seen them disintegrate and explode causing all kinds of damage. Better get it fixed soon.

 

Yeah I know right, it's soo loud, not what I expected from a brand new part from a seemingly reputable manufacturer.

 

I drove the Van today actually and for the first journey the fan clutch actually disengaged the fan and I could hear the engine, sounded sweet. But after turning off and starting my next journey it stayed engaged the whole time. 

 

I'm hoping to order a Genuine Nissan from Asia but want to be certain on a part number.

 

Wondering if this could be the one?

Screen Shot 2022-04-10 at 7.45.30 PM.png

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