Overheating, Whats Next?

[CallmeMaybe]

So I finally got my MJ started and first thing I did was watch the temp gauge. (previous owner blew headgasket) its currently 55 out and it was cool for about 4min then got pretty close to the red. I also noticed the electric fan didnt kick on. Tested it, works fine. Where should I go from here?

[banshee]

First question

Open or closed cooling loop?

 

Then is the system completely full of water/antifreeze?

And if so, I’d have to point at your thermostat... B...

[relyt120]

It really shouldn't overheat after 4 mins with or without the aux fan. To start I would pull the t-stat and see if it still overheats. Prob wouldn't hurt to change the coolant if you haven't and burp the thing to remove any air. As for the aux fan it could be that the relay is bad, if you have a/c see if it comes on with the a/c on; if it doesn't I would bet the relay needs to either be cleaned or replaced. not sure if you have done any of these things or not, certainly a good place to start. Also you should mention your truck year/drivetrain either in your post or your sig. to get better help. :thumbsup:

[CallmeMaybe]

Sorry new, '88 4.0L.

[relyt120]

I wasn't scolding! just letting you know. heck they had to tell me 3 times lol

[fiatslug87]

Was the top rad hose hot? Are you sure the system has been burped sufficiently? Assuming it's still the closed system.

[CallmeMaybe]

I really havent done anything yet, just got it running and wanted to check the temp.

[CallmeMaybe]

Anyone know the best way to drain the cooling system?

[my96z]

Anyone know the best way to drain the cooling system?

 

Pull the lower hose from the engine. I have had a few 4.0's come in and they either weren't burped correctly or the water pump isn't circulating. I have had a few that the impellers on the water pump were completely rusted off.. Is your coolant clean or are there signs that it was previously rusty coolant? If it is really rusty I would recommend a new waterpump.. If you want to burp it take the hot water line off the thermostat neck and fill it till you get coolant at the aluminum side of the connection.

[CallmeMaybe]

Pulled the hose from the radiator, from the engine and pulled the thermostat. Flushed threw all those points, replaced thermostat. left the cap of the resivoir which was filled the the max mark, and fired it up. got to about 210 and stil no fluid was moving threw any of the lines and resivour. What next? Why wasent it pumping? Also replaced my fan's relay and that still didnt come on. Ideas?

[Biotex]

I have had a few that the impellers on the water pump were completely rusted off.. Is your coolant clean or are there signs that it was previously rusty coolant? If it is really rusty I would recommend a new waterpump..

 

What next? Why wasent it pumping?

 

New waterpump maybe???

[Eagle]

Pulled the hose from the radiator, from the engine and pulled the thermostat. Flushed threw all those points, replaced thermostat. left the cap of the resivoir which was filled the the max mark, and fired it up. got to about 210 and stil no fluid was moving threw any of the lines and resivour. What next? Why wasent it pumping?

Because the thermostat didn't open yet. The thermostat is on the front of the engine. The sender for the temp gauge is on the left rear corner of the head, which is sort of a localized hot spot, so it always reads warmer than most of the rest of the system. That sender doesn't control anything, so it's not a foolproof indication of what the coolant temperature is at the thermostat.

 

How did you fill the system after flushing? Just pouring coolant in through the coolant bottle won't do it.

 

Also replaced my fan's relay and that still didnt come on. Ideas?

It didn't come on because the system wasn't hot enough. The aux fan on an '88 is controlled by the sensor in the driver's side radiator tank. Until the temperature of the coolant running through that tank reaches something like 210 or 220 degrees, the fan doesn't turn on.

 

BTW ... you aren't supposed to fill the coolant bottle to the top. It should be filled halfway when cold -- no more, no less.

[CallmeMaybe]

ended up just filling threw the radiator hose then topped off at the coolent bottle hose and burped the system. Now running no more then 200 at idle in my driveway for 15min.

[fiatslug87]