Radiator runeth over

[sick620]

New rebuild l20b..  trying to run an original 521 radiator for now… started truck let it warm up while topping off rad with water as it warmed up… water just sat calm in radiator cap off whole time .. I waited for water to start moving showing that the new thermostat opened up… seemed to take a long time nothing changing with the water in radiator … checked temp gauge not going up at all… grounded wire and gauge maxed out high temp so the gauge is functional maybe bad sender? Maybe no water passed thermostat so sender isn’t registering temperature?……

let it sit a couple minutes longer in case it just wasn’t warm enough yet still nothing on temp gauge still nothing for movement in radiator… then all of a sudden water starts flowing over out the radiator (where cap usually goes) fast and aggressive…fan misting it all over the place..had to shut it down….

 

before trying this old used radiator I tried a new Chinese one it was bad from the factory leaking all over the place, but it also did this wierd thing where it’s fine then all of a sudden without a build up etc it starts coming out crazy from the filler hole… 

 

since it’s all at once and so immediate id assume this is the thermostat opening up? I’ve never had a Datsun do this … 

 

maybe both radiators were plugged up restricting flow as the thermostat opened? 
 

Maybe head gasket or something is not sealed good? (No water In oil, oil in water, or smoke etc) it runs great idles nice etc…

 

maybe thermostat is not opening?but  I don’t know what else would explain the water calm one second then coming out of hole the next violently….

 

 

i tried filling back up and putting cap on… ran for a minute or two, no leaks or anything but still temp gauge not coming up .. squeezing upper radiator hose it is hot with pressure kinda difficult to squeeze… 

 

the thing making this extra hard is no way to judge temp should probably fix that first huh ?

 

 

Edited May 2, 2022 by sick620

[datzenmike]

Thermostat not opening. Water in block finally overheats and turns to steam. Can't get out through the thermostat, so pushes water out the lower radiator hose and radiator over flows.

 

Thermostats are cheap enough, just throw the other one away and replace it with a 180-F. Get a thermostat for a 521 not for an L20B. Spend over $8-$10 and get a good quality one.

 

 

[banzai510(hainz)]

12 hours ago, sick620 said:

maybe both radiators were plugged

take the hose off at bottom and flow a hose throw there and will be obvious. if water come out the bottom

 

also if one waits at idle for the stat to open youll be waiting a long time.

 

Yes some rads once hot will leak . = poor quality as most are made in china.

 

I would run this w/o a stat for right now and see water is flowing. and on a cool day it should run cold. If it overpressureizes then you know you have a proplem.

I always drill a 1/8 inch hole in the stat to act as a bypass if your 521 didnt come with one. Some do some dont  I can remember. My 51s were that way.

 

 

did the temp gauge work before?  if yes then I say the sending unit is good. grounding it out shows the meter is good but maybe not the brass sending unit. sand it then hook wire back up

[Stoffregen Motorsports]

Instead of running without a t-stat, take the valve out of the t-stat and install the remaining restrictor plate. This will make sure your engine isn't running too cool. It simulates an open t-stat.

 

Then once you verify everything else, install a new t-stat. Brand name.

[datzenmike]

So much easier to just throw away and replace once rather than dicking around. If not the problem you have a new one and it cost $10. This is why I never go to all the trouble to test them. If I suspect a problem I just replace.

[sick620]

5 hours ago, banzai510(hainz) said:

take the hose off at bottom and flow a hose throw there and will be obvious. if water come out the bottom

 

also if one waits at idle for the stat to open youll be waiting a long time.

 

Yes some rads once hot will leak . = poor quality as most are made in china.

 

I would run this w/o a stat for right now and see water is flowing. and on a cool day it should run cold. If it overpressureizes then you know you have a proplem.

I always drill a 1/8 inch hole in the stat to act as a bypass if your 521 didnt come with one. Some do some dont  I can remember. My 51s were that way.

 

 

did the temp gauge work before?  if yes then I say the sending unit is good. grounding it out shows the meter is good but maybe not the brass sending unit. sand it then hook wire back up

I am unsure if temp gauge ever worked because I never ran the truck long enough to know… I did try wire brushing the nipple so probably a bad sender huh?

[Stoffregen Motorsports]

No, they can take the wire brush.

 

If you have a multi meter you can check the sender.

[banzai510(hainz)]

well Its hard to arm chair guess but yeah I had a sender go bad. Then I tried to break it loose and CRACKED the whole lower housing as it was frozen in there.

So I think I used another lower housing with the sender already installed and it worked.

 

I got new spare housings now.

[Thomas Perkins]

Maybe bad water pump...When my temperature sender goes bad,the only thing happens is the temperature gauge is on the low side.My thermostat opens up just above the half way mark,then goes down below half way and stays there.

Edited May 3, 2022 by Thomas Perkins

[sick620]

On 5/1/2022 at 8:15 PM, datzenmike said:

Thermostat not opening. Water in block finally overheats and turns to steam. Can't get out through the thermostat, so pushes water out the lower radiator hose and radiator over flows.

 

Thermostats are cheap enough, just throw the other one away and replace it with a 180-F. Get a thermostat for a 521 not for an L20B. Spend over $8-$10 and get a good quality one.

 

 

Im trying new thermostat first, but why get a thermostat for 521 and not l20b? 

[datzenmike]

That would depend on if there is a thermostat by pass hose. It's a small metal pipe descending from the thermostat down across the front of the engine timing cover to the lower radiator housing. there will be a short hose on each end. If the L20B has this then YES use a 180F L20B thermostat definitely. All L20Bs will have this by pass you're right.

[sick620]

I got this thermostat from Napa autoparts… kinda cool it’s made in Japan 

 

as well as a temp sender from rock auto and installed today with the original radiator for now… 

 

temp gauge now working and temp gos a little bit above half and seems to stay there… 

 

Water seems to flow really slow in radiator so I think the radiator is just really plugged inside, we ordered a koyorad so hopefully that will be the end of our cooling problems.

[datzenmike]

 

All my Datsuns run a needle width above half in the 'run range' on the gauge with 180F thermostat.

 

Did that stop the overflowing? It should.

 

Scale inside the radiator is from decades of topping up with hard tap water that has dissolved minerals in it. Coolant boils away concentrating the minerals. Only use distilled water in your radiator for mixing and topping up.

 

Place rad face down with the cap on and fill with CLR and let sit for a day. I left mine 3 days, won't hurt anything.