Bleeding a 1990 4.0l cooling system

[slickdaddylube]

I’m having trouble bleeding the cooling system on my 4.0l ranger 1990 I’ve taken it to a shop, tried one of those big no spill funnels, replaced the water pump, thermostat , and rad hoses but temp still is unstable but never over heats, no oil in coolant or vide versa anyone have this trouble as well/have any tips?

 

[RonD]

If temp gauge goes up and down randomly then heater core is partially blocked
Easy to change on 1994 and earlier Rangers

And to purge all air from a cooling system, disconnect either heater hose at the firewall, and fill system until coolant comes out hose and core, all air is out, put hose back on

1990-2000 4.0l was notorious for cracked heads
This would cause AIR to be pumped into cooling system, so adds air and causes overheating, and can cause temp gauge to go up and down, but mostly up the more you drive it, and the overflow tank can "overflow", lol

So if you purge air using heater hose and still have the overheating issue then its a blocked heater core or cracked head

You can do Glove Test to check for cracked head, simple easy test

 

[Eddo Rogue]

When this happened to me, it was the heater core. Also "burping" the air out was a PITA, I found an in line bleeder valve and plumbed it in, worked like a charm.