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New Radiator Issues


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I looked to see if this has been posted before and had no luck. 


I recently put sidedrafts on my 75 710 L20B. Before I did, everything was in working order other than some smoking out of the tailpipe and I was driving the car daily. In the midst of installing the carbs, my radiator cracked in the core. I looked everywhere and had no luck in finding an original radiator or an aftermarket one that fit. So I purchased a universal radiator that was the same size as well as core size. 


Upon completion, I tested the car by letting it idle for about 15 min then did a short drive around my house. when I got back I didn't notice any leaking, however, I came across something odd. I noticed that the hoses from the top of the radiator as well as some of the bypass hoses were under terminus pressure, almost to the point that the hose was backing off their mounts. I checked the overflow and let the fluid drain from there and noticed that it was cold. I opened the radiator cap slightly knowing that it is under pressure and the coolant that came out was cold as well. Upon checking the radiator for heat I also noticed that the driver side was cool and the passenger side was hot, almost as if it wasn't cycling. 


The new radiator that was installed was 1/2 inch bigger in the out/inlet so the pressure should be less than the old one that was already working fine. The car was sitting for almost 2 months as we were working on this. Is it possible that something got frozen up while it was sitting that is not working properly now?


I attached some pics. Any help would be greatly appreciated. The pic with my finger in it shows the amount that plastic covering expanded since it was touching when I started. 






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That's what my buddy that has a Z said too. I wasn't sure if that could get rusted sitting there for 2 months after it was working properly. 


I assume that any L20B thermostat would work whether it is from a 510, 610 etc. If that is the issue, is there a certain one that I should get? I tried looking for one and it seems that they all say for a "Bluebird" and they're not the same year as mine.  

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Thermostat works on temperature it doesn't care what car it is in. Maybe as low as 170F but everything working a 180F should be fine.


Two things about the pressure....


1/ thermostat is stuck closed so no circulation and the water in the head boiled building pressure. You should have a 13 PSI rad cap. This will prevent an explosive 'let go' of any hoses or the rad... if they are in good shape. Replacing the thermostat should fix this problem.


2/ Failed head gasket. Compression which is around 150 PSI, (often more) is squeezing into the cooling system and pressurizing it. Normally the rad cap will vent fluid into the overflow or coolant recovery bottle. This will continue until the rad level is dangerously low.

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When installing my new thermostat, I noticed that the thermostat housing base where the screw goes in is stripped clean. I was looking to see if I could just find a new one while I'm at it, however, I can't seem to find one that matches mine. Where the sensor is on the front, I have 2 openings, one for the sensor and one where a coolant hose enters. The ones that are coming up im my search only contain one hole for the sensor.


Are there some years that are differ, or is it possible that someone changed the one on my car before I got It? I assume that I can't go with the one inlet hole type since I have that coolant hose. Any thoughts?

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So you need to run a hose from the other hole to the coolant outlet just below the fuel pump that points straight up at the fuel pump.

Normally you would have a coolant hose going from that outlet below the fuel pump to the intake manifold, and that line would have a "T" in it to go to that second hole in the thermostat housing, that is a bypass hose that you need, since you don't have the stock intake with the coolant fitting, you have to change that part.

The L16 came with a thermostat housing with only one outlet for the temp sensor, they had a hole in the thermostat as a bypass, but Nissan changed that and put in the bypass.

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Easy fix you can see what size the hole is and see what size tap will fit and retap the hole next size up..

I may be wrong but for an example...

I think the bolt on that thermostat housing was 8mm... if so 8mm is .3149...

A 3/8 -16 .. needs a hole of .3125.. you should be able to get a tap and tap the hole with a new bolt.. may have to open the matting hole on the cap a little to allow for the slightly bigger bolt...

Here's a drill and tap chart for reference...


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Yes you can over size to a standard or metric bolt... whatever is easier/cheaper.




While you are at it drill a second hole in the thermostat housing for the water bypass hose. Tap it for a fitting like this one or whatever is easiest. Doesn't have to be metric..... it just has to work.

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It's self bleeding. The thermostat is the highest point on the engine cooling system and the engine is tilted up slightly to the front also. At the latest, as soon as the thermostat opens, any air is emptied into the upper rad tank. Vertically mounted thermostats have a jiggle valve for doing just this. Horizontally mounted ones self empty.

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you haven't searched enough.


I have my vid.  olddatsuns.com the tech section had a link to it if you even went to that best site on getting info

look up Hainz Datsun L series on YOutube.


But its more a whole motor that Im doing.

You need to get a Datsun L series chain wedge and a good 10mm hex and have a good torg wrench, breack bar 1/2 in and the 1/2 to 1/4 adapters.


later Datsun the intake is a MOFO to get the bolts out so your on your own


before going off what does the temp gauge say?????????????? themp sender is on the motor side and if it not overheating don't do anything yet.


ck the spark plugs . If one look jet CLEAN then yes its sucking water in.

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