Running hot

[DaveB]

Hi Les,

Haven't heard from you for awhile. Been busy?

Your truck shouldn't be running so hot. Although I don't have a defender to compare, I'm sure the defender drivers will tell you the same thing.

The three primary reasons for overheating are plugged up cooling system (internally), dirty plugged rad (externally) and air in the system. And also, inoperable thermostat...

If you've recently flushed it out, I would think internally plugging is unlikely, however, you may have a big air bubble somewhere in the system. this is usually caused by draining the cooling system for the flush, then when filling you get an air lock where the heater hoses haven't filled. As that moves around the system it can cause it to run hot.

I would pull the thermostat and put it in a pot of water and bring it to a boil to ensure its opening just before the water boils. If not, get a new one. Also, when refilling, remove the top heater hose and fill until antifreeze dribbles out both sides of that connection. You will then have very little air in the system, which will bleed itself off on its own.

Also check in front of the rad (and any other coolers up front) to see its not caked with mud, leaves, etc., which hamper airflow and don't transfer heat well. A pressure car wash can usually do a good job of cleaning this out and can make a real difference.

Dave

[exmod110]

Also check the viscous fan!!
Very hard to diagnoise, when hot the fan should be almost locked up and be very noisy off idle. Also if you have the t stat out make sure it opens completley, I had one that would come up to temp in the shop and stay at norm temp.. road test and would overheat.. t stat would bined about quarter open...


Don

[exmod110]

not onl viscous fans but eletric fans for proper cut in at correct temp and operation
an infra red heat gun helps for this, also lets you know if gauge is accurate