Datsun 521 Cooling/Overheating issue

[Rattlehead]

On to another issue I'm facing. I've checked many posts on the overheating topic.

 

New koyo rad, New hoses, New thermostat(twice)

So my iissue is when I start the truck up(cold start, or after it sits for a while)

It tends to start overhearing,( I watch the gauge go passed 200-220)I shut it and the hoses have a lot of pressure.

I undo the cap. Let the pressure out then after a second time. After the second time the temp gauge drops, as it should

as if the thermostat finally opens. From then, the Temps don't climb and if they do, they climb back down normally 

with the thermostat opening. I've even left the truck running for 20+ minutes with no issue.

 

No smoke from exhaust, radiator stays full, heatercore bypassed(got it like that), used funnel to bleed air

I drove it home when I bought it, this only started happening as I was fixing and replacing parts

I haven't replaced water pump, but it's on my list

 

[jagman]

What is your radiator cap pressure? It may be too high.

[MikeRL411]

Thermostat lacks a jiggle?  Needed to allow hot water to reach radiator and also temp sender

[Rattlehead]

[Rattlehead]

@jagmanthis is the cap i have, maybe its too much? I actually didnt check before buying, so maybe this is the issue?(I hope so that would

make this so much easier(I replaced my old cracked champion radiator) 

Although i cant find other koyorad caps with a lower pressure rating

 

@MikeRL411The thermostat does have the little opening thing. since engine has a slight angle, i placed it on the high side

 

 

[datzenmike]

Rad cap you have is 18 PSI should be 12-13 PSI. Rad cap is not going to cause over heating.

 

 

 

Thermostat should be 180F. Cut that brass jiggle valve off to open that hole. Place the hole on the far side away from the head when installing.

 

 

The water around the thermostat is static while the thermostat is closed. It remains cold/cool while the engine internally begins to over heat. A small hole will allow some flow past the thermostat and into the radiator. This way hot internal water slowly flows up and past the thermostat and it can sample it and open properly.

 

[Rattlehead]

@datzenmikeOk ill get rid of the brass thing, I got the 180 stat from rockauto, and I have the autozone one because i needed to test a different one fast.

so then i should try and find a different cap for my koyo?

 

[Rattlehead]

UPDATE: I cut the brass part on the thermostat leaving the 1/8in hole uncovered. The truck held 180 temp for over 10min. 

I did have the funnel on for bleeding, so I plan to do it again later after it cools down and see what happens. So far its looking good🤞

[datzenmike]

Well too late now but did you place the hole as far away from the head as possible? This will draw internal hot water through the thermostat so it can react. It'll still work though to dispel the cold stagnant water.

[Rattlehead]

@datzenmikeYes i placed it away from the head of the engine

[Rattlehead]

Thanks for the help everyone I got it all sorted out

On to the next problem😅