O.k heres one for all you cooling system guru's.
I have a stock L20B with a 3row recored standard 1600 radiator.
For the last few months (maybe longer as ive been topping it up for ages), its been losing water out of the radiator.
Its definitely coming out from the radiator cap.

When i last filled it up, it was fine driving 30mins to work, but after work i got 10mins down the road and heard a funny glopping sound from inside the engine bay and the temp suddenly went up to a little over half.
I've heard it do this before a few times but never looked to see what happened.
This time though I pulled over and found water everywhere, especially on top of the radiator. It seems there was too much pressure in the system and the cap gave way as it should.
Now, this is what i think is happening...
The radiator is doing too good of a job cooling the water and the thermostat is hardly opening (explaining why my heater is nearly always cool) and when it does (after hard driving or a hot day idling in traffic etc) the flow of water rushing into the radiator (which has already pressurised somehow) bursts the cap and all the water flys out.
I hope that made sense.
I'm not the best on cooling systems so any ideas on how to fix this would be greatly appreciated...

I'm going to get a new cap and thermostat for starters but dont think it'll be as simple as that...

actually - a new cap sounds like the fix. but the gurgling sound...? your thermostat might be "sticky" for lack of a better word (ie corroded) and not operating correctly. if you're losing water out of the top of the radiator it could also be your overflow line having a split.

most datto heaters get shagged quickly though which explains your cold heater - i always hear how someone got a mint datto "and even the heater works"...

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frankenstein projects R us.

The Republic of Western Australia -
Propping up the Nation's Economy since 1901.

I had a similar problem with my L20B, how low is the water whem you top it up, if it's not down to the core i would just leave it, at least thats what i found, the car never got hot, but if i filled the rad to the top, it would just expunge some after a bit of a drive and then wouldn't do it again. More info would help.

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Vaughan
'70 P130 Super 6
Fiesta XR4 (modified)
Formally: 510 L22B twin webber terror
510 FJ20et (510 FJ)

when/if you get to the thermostat, check to see if it has a 3mm hole or there abouts drilled in the shroud. if thats the case i'm 99% sure that you've found the problem.

An air bubble forms at the top end of the thermostat meaning it doesnt heat up early enough to open before the water expands and overflows <- do a search on that one i think baz explains it in full somewhere on why / why not to remove the thermostat and how much restriction is needed if you do.

double check your heater too (flush it seperate to the block and radiator) i had the pleasant experience of mine dumping nice boiling dirty stinky rusty water all over my feet as i was pulling onto the freeway not so politely

it usually dumps out more and more.
I top it up everytime i can see the top of the cores.

The heater was flushed recently as was the radiator and both flowed fine...??? the heater tap works fine too...

yep, sounds like a dud cap to me!

_________________
frankenstein projects R us.

The Republic of Western Australia -
Propping up the Nation's Economy since 1901.

it could be your cap, I'd check that out. However I think it's more likely to be the thermostat. Not too long ago my thermostat (in my L16 Stanza) needed replacing - it wouldn't open soon enough so the water in the engine would heat up too much, and when the thermostat finally opened it would cause a lot of steam and water loss and such, and would sound pretty terrible when it did so. Replace it with a genuine one if you can. Just as an elimination measure, make sure there's no wet patches around your transmission tunnel from a leaking heater, and that all your hoses are good.

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Iain
Datsun Stanza GX
AKA "Stanley", "The Brown Bullet"
5 speed dogleg box, mechanical secondary throttle, Bluebird S2 radiator & fan, off-road spotties, paralysed nodding dog, "invisible dashboard", Volvo cold air duct

had the same thing with my XB Fairmont acturly. its a 302 V8 turned out to be the Thermo. anyway it also leaked from the thermo housing cause it turned out that the guy who replaced the thermo befor i did made his own gasket outa a Porn mag... dont ask me how lol. got quite a shock when i took that off.

Rob

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theres nothing like driving a 4 banger unless its a V8 lol

I drill a 1/8 bypass hole in the state.

Make sure bottom hose is not collaping, Soft

If running a water line like the old L16 style is the head drilled for the water passage? Otherwise its a air pocket.

get new cap and stat as the others said

just a follow up:
i replaced the radiator cap and thermostat with new 'tridon' brand ones from Supercheap.
I noticed when i removed the old one that it didnt have the small hole in the old thermostat and the new one has a small brass bit in a hole (sort of crude oneway valve).

Anyhow, drove to work now a couple times in 30 degrees etc and it hasnt lost any water so far.

'fingers crossed'....

That "small brass bit" is known as a "jiggle valve".
It allows air to purge from the system and collect at the highest point, hopefully the radiator cap.
If you haven't already, fit an expansion tank to the cap overflow pipe.
Then, with a coolant recovery cap, the engine can burp out fluid/air and when cooling, suck back fluid ensuring the system remains free of air

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Regards, Graeme
Just trying to help...
http://nissanman.shutterfly.com/
graemes@internode.on.net

just when i thought everything was going fine and i was about to wipe my hands of this problem, the sh*t hit the fan!

Drove out the other side of town today in the hot weather.
Got to the city when i missed a set of lights as the que of cars was so long.
Finally took off from the second green light and as i was going through the intersection, water started spraying from out the rh side of my bonnet all over the front of my car and a bit on the windscreen.
This in itself was nothing different to what has been happening over the last few months anyhow so i kept driving and watched the temp guage alot closer.
Next time i stopped at a set of traffic light and took off the same thing happened. Now this had never happened before. It lasted a good minute this time.
Temp guage went to halfway (this is hot)!
Pissed off and still thinking it was a thermostat issue of some kind i kept driving.
The next set of lights i stopped at there was light steam coming from the engine bay.
Kept driving. I didnt have far to go till i stopped anyhow.
Then the car started to (ping?) and rattle badly like a metallic sound of some sort. It got worse and worse and i thought 'stuff it, i'm sick of this engines niggly problems' and tried to break it properly this time by keeping on driving it.
The noise got worse and worse and the power started to drop and drop until i couldnt hold my speed with even more steam coming out the engine bay which is where i shut it off and rolled into a carpark to stop. Hoping i did enough damage that it could be easily recognisable this time as to what the problem is that has been plaguing this engine for so long.
When i lifted the bonnet there was steam coming out from between the rocker cover and the head and also the radiator cap when i removed it.
While waiting for the tow truck i checked all four spark plugs which all looked fairly normal. None were damaged or welded together etc.

I can only assume that for all this time there has been a crack in the head or some problem with the head gasket that finally let go today with the heat and long drive combined.
I'll start fixing it tonight and hopefully put right what has been annoying me for so many months...

If anyone in adelaide has a good U67 or A87 head they are willing to part with please pm me as i may need one in the next day or two.

Cheers.

I've got one sitting around but it has a little foreign object damage in one of the chambers.

Got a new never fitted one Nick.
also a good runner 20B

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A little knowledge is a dangerous thing.
www.datsport.com

"R.I.P. Baz. 29 April 2022. Thank you for all your contributions to the Datsun community over the years. You will be missed." - OZDAT

thanks for offers zac and baz.

I got the head pulled off early this morning and to my surprise it wasnt all that bad.
The head just about fell off the block though so it couldnt have been sealing too well.
There was a brownish stain between cyls 2 and 3 and cyl 1 had a coolant channel corroded very close to the metal cc sealing ring which i guess is what finally pushed all the water out the radiator yesterday. This would explain why when leading up to this it occasionally dumped water out the radiator when it got real hot.
I still dont understand why it pinged so bad and lost so much power that i couldnt hold any speed? or is that from water being pumped into the cc??
Thought i'd broken something in there as it died!
I'll take the head and the head gasket down to Lonsdale cyl heads today and see if they can enlighten me further.
The head is ported out too and has sentimental value as its off my very first 1600 i ever owned, so hopefully its alright as it did go nicely beforehand on every motor its been on.
Cross fingers its just some welding of those coolant passages and a minimum machine to true the head again and new gaskets all round...