82 Datsun Caravan (Z20)

[datzenmike]

 Yes

[richURVAN]

On 12/18/2021 at 3:17 PM, datzenmike said:

 Yes

 

Drained the coolant and flushed the system from different directions . . . then filled the radiator back up with water and a chemical flush, and bled the system as per a number of different YouTube video's. 

 

It didn't have a Thermostat in it so I left the replacement one I got out for now (thought why complicate matters) and ran it round the block to test and it still overheats.

 

So there wasn't a Thermostat in it to not fully open and hinder the flow of coolant, so I'm betting the water pump is the culprit now. I'll inspect that tomo and possibly swap it out.

 

Unless I haven't bled the system properly but I done it a bunch of times, with the reservoir topped up, heater on hot, rad cap off and squeezing the top and bottom hose until the bubbles rise up, and then whilst the engine's running as well. 

[datzenmike]

Water pumps don't have much that can go wrong that they don't pump water. Fan belt could be loose or glazed and slipping. Clutch fan may be slipping. The bearing can fail but you would hear the noise made by it. The only other thing is the seal can begin leaking but the impeller inside is reliable. 

 

 

 

The top of the radiator is the highest point in the cooling system so air bubbles will naturally seek to go there. Any bubbles caught behind the thermostat will escape once it opens... then just top it up. I don't know of any Datsun or Nissan that has to be bled of trapped air.

 

Can you take pictures of the needle position when it 'overheats"? It may be within what I call normal. Don't forget the Vanette (here) was discontinued for exactly the same reason... overheating, because Nissan could not solve this problem.

 

Overheating is caused by two things... lack of air flow or lack of coolant flow.

 

Lack of air flow

1/ external radiator fins blocked by leaves, debris, bugs

2/ grill blocked by fog lights, bush bar, license plate...

3/ clutch fan not working properly, Blade missing?

4/ fan shroud missing. The shroud increases fan efficiency.

5/ loose, glazed fan belt.

 

Lack of coolant flow

1/ bottom rad hose soft and collapses at higher revs from water pump suction. Feel it or rev up and watch for collapse.

2/ radiator internal tubes are blocked by hard water scale. Look in radiator cap opening. Use CLR to dissolve the scale.

3/ wrong heat range or faulty thermostat. Don't waste time testing it!! Just replace it!!!!

4/ low rad coolant level. 

5/ heater leaks, so both heater hoses are joined in a closed loop. If doing this be sure to block flow from one to the other.

 

Also ran...

 

1/ blowing or blown head gasket

2/ very retarded timing.

 

 

Continue replacing the thermostat. It could fix everything. It might be stuck and this would delay warm up and not open fully causing high speed overheating.

 

[richURVAN]

11 hours ago, datzenmike said:

Water pumps don't have much that can go wrong that they don't pump water. Fan belt could be loose or glazed and slipping. Clutch fan may be slipping. The bearing can fail but you would hear the noise made by it. The only other thing is the seal can begin leaking but the impeller inside is reliable. 

 

 

 

The top of the radiator is the highest point in the cooling system so air bubbles will naturally seek to go there. Any bubbles caught behind the thermostat will escape once it opens... then just top it up. I don't know of any Datsun or Nissan that has to be bled of trapped air.

 

Can you take pictures of the needle position when it 'overheats"? It may be within what I call normal. Don't forget the Vanette (here) was discontinued for exactly the same reason... overheating, because Nissan could not solve this problem.

 

Overheating is caused by two things... lack of air flow or lack of coolant flow.

 

Lack of air flow

1/ external radiator fins blocked by leaves, debris, bugs

2/ grill blocked by fog lights, bush bar, license plate...

3/ clutch fan not working properly, Blade missing?

4/ fan shroud missing. The shroud increases fan efficiency.

5/ loose, glazed fan belt.

 

Lack of coolant flow

1/ bottom rad hose soft and collapses at higher revs from water pump suction. Feel it or rev up and watch for collapse.

2/ radiator internal tubes are blocked by hard water scale. Look in radiator cap opening. Use CLR to dissolve the scale.

3/ wrong heat range or faulty thermostat. Don't waste time testing it!! Just replace it!!!!

4/ low rad coolant level. 

5/ heater leaks, so both heater hoses are joined in a closed loop. If doing this be sure to block flow from one to the other.

 

Also ran...

 

1/ blowing or blown head gasket

2/ very retarded timing.

 

 

Continue replacing the thermostat. It could fix everything. It might be stuck and this would delay warm up and not open fully causing high speed overheating.

 

 

Thanks Mike.

 

The needle got up to 3/4 of the way yesterday and I could hear the water boiling inside, def overheating!

 

So running through the causes for overheating (AND MY RESPONSES IN CAPITALS);

 

Lack of air flow

1/ external radiator fins blocked by leaves, debris, bugs - CHECKED AND CLEARED ANY DEBRIS

2/ grill blocked by fog lights, bush bar, license plate... - NOTHING BLOCKING AIR FLOW IN FACT I'VE REMOVED THE GRILL FOR NOW 

3/ clutch fan not working properly, Blade missing? - I DON'T THINK THE FAN CLUTCH IS WORKING PROPERLY I.E. IT'S VERY NOISY PULLING AWAY IN 1ST, 2ND GEAR AND STAYS ON HIGH DURING HIGHWAY SPEEDS?? ON THE CONTRARY THOUGH THIS SHOULDN'T CAUSE OVERHEATING IT'S JUST BLOODY ANNOYING

4/ fan shroud missing. The shroud increases fan efficiency. - FAN SHROUD INTACT

5/ loose, glazed fan belt. BELT IS TIGHT AND DOESN'T APEAR GLAZED

 

Lack of coolant flow

1/ bottom rad hose soft and collapses at higher revs from water pump suction. Feel it or rev up and watch for collapse. - HOSES HAVE BEEN REPLACED PREVIOUSLY AND ARE IN GOOD CONDITION BUT I WILL OBSERVE NEXT TEST RUN 

2/ radiator internal tubes are blocked by hard water scale. Look in radiator cap opening. Use CLR to dissolve the scale. - THE INSIDE OF THE RADIATOR DOES LOOK PRETTY BROWN / RUST COLOURED 

3/ wrong heat range or faulty thermostat. Don't waste time testing it!! Just replace it!!!! - THERE IS NO THERMOSTAT IN IT 

4/ low rad coolant level. - HAS BEEN REFILLED TO THE TOP 

5/ heater leaks, so both heater hoses are joined in a closed loop. If doing this be sure to block flow from one to the other. - NO LEAKS AT ALL AS FAR AS I CAN SEE 

 

It could be the head gasket starting to blow but there is no milky oil, no smell of exhaust in the rad, no exhaust smoke, and no power loss.

 

I will replace the fan clutch this arvo and see. But maybe it needs a new rad, I've flushed it out several times both directions and with chemical flush but as I say it does look pretty rust coloured inside.

 

Ta, Rich 

[richURVAN]

Quick update . . . fitted the new Thermostat which seems to be working as the the rad cap stayed cool until the temp gauge hit about halfway, then once opened the hot coolant was 'pumped' back into the top radiator hose.

 

I watched the temp gauge get up to almost 3/4 then noticed the water in the reservoir boiling and coolant coming out the overflow hose.

 

The fan's are not bowing hot air though and shouldn't one of the heater hoses be hot to touch? Both are cool. So it seems there is a blockage somewhere or the pump is not doing it's job. 

[datzenmike]

Heater must be in the ON position to allow flow through the hoses. Next time, or if you heed heat from the heater right now, lower the radiator water and disconnect the heater hose on the side of the block just above the starter and the other one where it connects to the fitting on the underside of the intake. Set the heater control to high heat and direct a garden hose into one of the hoses to flush sediment and crap out of the core. Now reverse the flow and go back and forth several times till it runs clear.

 

3/4 won't be hot enough for boiling. However if the head gasket is blown, compression will push out and into the cooling system and over pressurize it and escape into the over flow. It will bubble and look like it's boiling. I asked a long time ago if you were constantly adding water to your radiator to top it up. 

 

 

Did you ever re-torque your head bolts???? If head gasket is leaking it may be too late as this prevents rather than fixes the problem. Might be worth a try if a small leak, but at the end of the day you may be looking at replacing the head gasket. This is well withing the range of an owner with a few wrenches and being careful. You can do it for the cost of the head gasket about $30 Canadian.

[richURVAN]

12 hours ago, datzenmike said:

Heater must be in the ON position to allow flow through the hoses. Next time, or if you heed heat from the heater right now, lower the radiator water and disconnect the heater hose on the side of the block just above the starter and the other one where it connects to the fitting on the underside of the intake. Set the heater control to high heat and direct a garden hose into one of the hoses to flush sediment and crap out of the core. Now reverse the flow and go back and forth several times till it runs clear.

 

3/4 won't be hot enough for boiling. However if the head gasket is blown, compression will push out and into the cooling system and over pressurize it and escape into the over flow. It will bubble and look like it's boiling. I asked a long time ago if you were constantly adding water to your radiator to top it up. 

 

 

Did you ever re-torque your head bolts???? If head gasket is leaking it may be too late as this prevents rather than fixes the problem. Might be worth a try if a small leak, but at the end of the day you may be looking at replacing the head gasket. This is well withing the range of an owner with a few wrenches and being careful. You can do it for the cost of the head gasket about $30 Canadian.

 

Hey Mike,

 

So I already flushed the heater core and hoses in forward and reverse until clear. I'm starting to lean more towards it being a head gasket and the previous owner telling porky pies to me (said he hadn't been topping up the water in the rad). I've ordered one of those chemical combustion leak tests to be sure.

 

I'll re-torque the head bolts (doubt the prior owner did them) and see if that get's me out of trouble for a short while. But yeah looks like head off, appreciate the encouragement, is there a sticky/tutorial anywhere on the forum? What are my options with the cylinder head, reconditioned? Replace with new part might be cheaper? Performance head for few extra bucks? Or just clean and replace and hope for the best?

 

Ta, Rich 

[datzenmike]

Never mind the head bolts I saw that you have the Z20 and only the Z24 suffered from this.

 

No need to replace the head just the gasket. It would be prudent to check that the head is not warped or it will blow again. Easy enough to do after cleaning. There is no performance head for the Z series. They are a good design for efficiency and low emissions. It's not a good design for power. It is what it is.

 

 

 

 

[richURVAN]

On 12/23/2021 at 2:14 PM, datzenmike said:

Never mind the head bolts I saw that you have the Z20 and only the Z24 suffered from this.

 

No need to replace the head just the gasket. It would be prudent to check that the head is not warped or it will blow again. Easy enough to do after cleaning. There is no performance head for the Z series. They are a good design for efficiency and low emissions. It's not a good design for power. It is what it is.

 

 

 

 

 

I ended up with a Z24 in the end.

 

So I've got one idea to run past you Mike . . . 

 

I'm starting to think it might not be the head gasket (which I'll confirm this week with compression test and combustion leak test) but to do with the fan / fan shroud and/or rad.

 

I noticed that the fan is sitting almost outside of the shroud (closer to engine) so is pulling air from all around the rad and not necessarily enough directly through it. I spoke to a radiator place thinking next stage would be to get the rad re-cored, and he suggested this could be causing the issue. What's your thoughts? 

 

Because the water pump and fan clutch on the engine are separate replacement parts and are shorter in depth than the original all-in-one unit. So I'm hoping there is some kind of spacer out there that I can get hold of. Any idea this part exists for the Z series fans? 

 

Ta,

Rich 

[datzenmike]

I would definitely re-torque the head bolts ASAP as this is a known problem. A compression test does not always indicate a blown HG till it's dire. A leak down test is better for this.

 

There are some obvious differences between ours and yours. Ours was only around for 3? years and they had over heating problems.