99 Wrangler Sport Overheats when idle

[Steve Moss]

I've read some similar posts, but can't find anything like my situation. '99 Sport, I've taken good care of this thing. I bought it new, it only had 65000 miles today. Anyway, I replaced radiator and water pump in 07 and heater core last year. Recently, I had a freeze plug that had developed a pin hole and I replaced them all. Now, my commute is only 2 miles and I could drive that with no problems at all. I could idle the engine all day and it would never get hot. I started it 15 minutes before I left for work every day to defrost and heat up with no problems. Heater was working great. I seldom drive it much further than the commute, but a week ago I drove it about 10 miles and the engine started getting hot. It never reached red, but coolant was going to overflow and spewing. When it hit the radiator I saw some steam.... so anyway, I jump on here and think it must be the thermostat from reading similar posts. This is where it gets odd...

I replaced thermostat and start engine up to idle. When idling, within 5 minutes needle goes to red and system is HOT. Before putting this thermostat in, it could idle all day without getting hot. Other odd thing, now heater is blowing cold air. I can't get heat. I turn engine off and let it cool. After it's cooled, I pull radiator cap so I can check circulation. About 1 minute after starting up, coolant starts spewing from the radiator... what in the world? I'm lost. No smoke from exhaust...


Hope you pros can help me out...

 

[wwch99tj]

Make sure you got all the air out of the system.

Sent from my Samsung Galaxy S3 using Jeepz

 

[Steve Moss]

Thanks, but can anyone give me a good method for doing this? I pulled the radiator cap hoping it would do just that and it spewed fluid everywhere after running for just a minute.

 

[JPNinPA]

Few items, air in the system, radiator cap. Though I'd have to say if you rotted out a freeze plug you should do a good flush and fill of the entire system. Rot equals buildup. Had it happen to me in an older vehicle. Rad was plugged.
PS if it initally (10 mi drive) got hot while driving above 35 mph it is on the cooling side. Clutch fan, blocked radiator, even water pump. ESP if you normally maintain 195 to 210 deg otherwise.

Was the thermo you pulled out bad?

Burping The system. Raise the Front of the jeep by parking on a hill or put it on jackstnds. With the engine cold, remove the radiator cap and top it off. Start the engine and as it comes up to temp watch that he fluid is moving. You should see a stream of large bubbles come out as the thermo opens. Help it by squeezing the upper hose. Once it appears to stop top it off and cap it up and shut off the engine. Be sure the overflow holds fluid and is filled correctly.

 

[jfrabat]

It could also be that the new thermostat was dead on arrival; you can easily see if the thermostat is good or not by starting the engine with the radiator cap off. Once up to operating temperature, you should see the flow start. If you have flow once you reach operating temp, the thermostat is good. Just be sure to shut the engine BEFORE it overheats!

I agree with the post above, though, that you need to flush your system... Sure sounds like the radiator is clogged. Of course, this assumes that you have watched the fan to make sure it IS coming on... If not, check it. This would explain rather well why the Jeep does not overheat when rolling and it does while sitting still. If it is the clutch fan, and easy upgrade is to just drop by a junk yard and buy a Ford Taurus (mid 90's) or Lincoln MK IV (IIRC; could be a different number) fan. I prefer the Lincoln fan because it fits the TJ radiator PERFECTLY! Then just use a relay and a switch to control it (or get a control box; Delta Current Control and Flex-a-Lite both make them).

 

[Steve Moss]

I flushed the system out very good after the freeze plugs were replaced. The coolant in it now looks clear. I went through all of the burping procedures and still nothing. I tried a 2nd thermostat and still same problems. I then removed the thermostat and tried it without it in.... still same problem. My water pump is just a few years old, but maybe it's corroded by what caused the freeze plug to rot... I'm thinking replace water pump now, sound right to you guys?

When I started it without the thermostat in, water never moves in the radiator, there is no circulation at all. When I killed the engine, I squeezed all of the hoses and can see movement in the radiator when squeezing hoses so I'm thinking there is no blockage. Water pump seem right? As bad ad it seems since it's so young...

 

[wwch99tj]

Sounds like the impeller is corroded.
I'd try replacing it ... at least its not an expensive part

Sent from my Samsung Galaxy S3 using Jeepz

 

[JPNinPA]

I flushed the system out very good after the freeze plugs were replaced. The coolant in it now looks clear. I went through all of the burping procedures and still nothing. I tried a 2nd thermostat and still same problems. I then removed the thermostat and tried it without it in.... still same problem. My water pump is just a few years old, but maybe it's corroded by what caused the freeze plug to rot... I'm thinking replace water pump now, sound right to you guys?

When I started it without the thermostat in, water never moves in the radiator, there is no circulation at all. When I killed the engine, I squeezed all of the hoses and can see movement in the radiator when squeezing hoses so I'm thinking there is no blockage. Water pump seem right? As bad ad it seems since it's so young...

Sounds like but I'd still do he flush while your at it. Even flush he heater core in both directions. While they may be whistle clean my experience wit rotted freeze plugs was there was buildup everywhere and lots of it. One other item. Check your lower radiator hose. Stock has a spring in it to keep it from collapsing. If it does collaps there will be no flow and you will overheat. Check by revving the engine while inspecting the hose.

 

[Steve Moss]

It was the water pump. It had no fins whatsoever. I guess the gunk in there was pretty bad. It's running clean now, but I think I better keep a good look at it. Is there anything I can mix in the coolant to work like a rust out preventative?

 

[JPNinPA]

The best is to flush it all out, correctly mix the proper coolant and keep it fresh. I've used Preston's super flush to remove a lot of buildup. HOAT or Zerex G05 and distilled water. As for adding anything. Not really as it may collect on the metal and areas you need the coolant to draw the heat from. This will lead to other problems like warped cylinders, heads...