it puts out just enough while driving in town, but at highway speeds about 10 min. of it and the heat goes cold and the engine is not overheating. The water pump, thermostat and heater core all work. Is it possible because of the high RPM's that it is bypassing the heater hoses?
Heat
- Thread starter 76chopper
- Start date
What's the enginne temp when the heat goes cold. On my cj7 in the winter on the freeway it gets so much cold air through the radiator that the engine doesn't get hot enough to have really hot air out of the heater. Try taking a piece of cardboard and slide it through the grill to block a portion of the radiator. The engine will run warmer. They make a cover that you put over the grill (vinyl with snaps ) just for that. I''ve used cardboard and also the cover.
mysunnshine
Legacy Registered User
- City
- Phoenix
- State
- AZ
I'd guess the thermostat isn't closing all the way but what did I know, I live in a hot climate.
Try holding the heater hoses when it's hot and you get the cold air. If their cold then you know coolant isn't circulating through or it's cool coolant. If the coolant is low, it might be low and sucking air (air pocket, like when you change the radiator and you need to burp the air out). When you shut it off and it sits, maybe the air works it's way out? 
. I have no idea if the thermostat would control coolant getting to heater core (haven't worked on a 4.2 in years, would have to check). If the thermostat was open or part way open, wouldn't he engine temp be cooler than normal since the coolant would be going through the radiator all the time while it's open?
. I have no idea if the thermostat would control coolant getting to heater core (haven't worked on a 4.2 in years, would have to check). If the thermostat was open or part way open, wouldn't he engine temp be cooler than normal since the coolant would be going through the radiator all the time while it's open?
- City
- Poynette
- State
- WI
I've owned 4 CJs all with the straight 6 and all with the hardtop. Driving around town was ok but highway speeds the Heater never kept up with the heat. I would reverse flush the heater every fall to get the rust and crud it of it. I assumed the radiator was so big and the engine compartment was so open the engine ran cold so I would run with a piece of cardboard covering the whole grill. On warmer days I could pull it out. This worked fairly well for me. Once I was driving on the interstate is was a below zero or near zero day and the carb froze up. Crazy. I don't take my Scram out in the winter so it's not a problem for me now lol. My LJ though is nice and toasty!
- City
- Molalla
- State
- Or
I think Skiptown nailed it. Heater core needs to be cleaned or replaced. Poor circulation through the heater core. And while you are at it, if you have to pull the heater box, change to the YJ blower motor.
- City
- Ashburn
- State
- VA
Did these to mine a year and a half ago 8 guess. Made a huge difference. I am betting the heater core swap will help a lot.
That's it. Remove both heater hoses and try to flush it out. Put the hose to the cold side first to see if you can back fllush it out. If you go the other way you may pack it in tighter. Easier to do than a new core. If it doesn't work your only out time.
- City
- Ashburn
- State
- VA
Seriously. Do the blower while you have it apart. It Is not an expensive part and worth it even if you don't notice the difference. Even though I did and I think the PO already did it since I did not have to cut a bigger hole.
If you are doing the heater core, do the whole box. Here's a thread on how to do it (I've done two, just finishing the second to put on a shelf as a spare). http://www.jeepforum.com/forum/f8/cj-heater-box-restoration-pic-heavy-975999/ If you have it apart might as well do it right.