Engine not reaching proper temp/no heat??

Ive got an 87 cherokee 4.0L and I have noticed that it doesn't seem to reach the proper operating temperature. After driving it 30 miles at highway speed to school in the morning the temp gauge is just barely at the first notch above 100*. Since it seems my engine is not reaching the proper temp my heat is also quite lowsy it has just a slight hint of warmth. My first thought was that the thermostat was probably stuck open so I went ahead and replaced it and i also put cardboard in front of the grille but it didnt fix the problem. Its below 0 around here and working out side sucks so i decided to take it to a local shop to have him try and fix it. He also replaced the thermostat that I had just put in 3 weeks prior and what do you know.....still no heat and no proper operating temp. Now my temp gauge seems to be functioning properly it doesn't swing wildy at all, it just starts out normally and slowly rises as the engine heats up, but never no matter how far I drive will it ever reach the proper temp. Does anyone have any ideas as to what could be causing my jeep to not heat up? is the gauge sending unit possibly failing? bad heater core(I will check the heater core lines tomorrow and see if their warm). Im kinda at a loss since the gauge seems to be working. Any help is appreciated.

I was going to say replace the thermostat, seems you already have that handled... radiator blockage too... see if you can borrow one of those nifty point and shoot IR thermometers, point it at the head or thermostat housing.

If that says you're operating at a good temp, definitely check your heater control valve, vacuum lines that feed it, and gauge sender.

Pop the hood.

Find out if the engine is warming up (it probably is). Drive it for 20 minutes, then stop and pop the hood. If you leave the engine running be careful of your fingers. Reach in and feel the upper radiator hose--it should be plenty hot.

Now, remove the temperature gauge sending unit wire and ground it with a short jumper. Check the gauge. Is the gauge pegged full hot? If not, you have a wiring/gauge problem. If it is, then replace the sending unit.

Now, you didn't mention the engine, so I'm guessing here. You should have a coolant control valve on the passenger's side of the engine bay near the firewall. The heater hoses run to it, and then through the firewall. Both hoses should be hot. If not, then your vacuum operated coolant control valve is broke, you have lost vacuum to the valve, or your heater core is plugged.

Good Luck.

Thanks guys, Ill try and get ahold of one of those thermometer guns tomorrow and I will check the heater lines and check the gauge, Ill let you know if I figure anything out. thanks.

Infrared point and shoot thermometers are invaluable for troubleshooting cooling, heating, and AC issues. Great for use around the house too. And through the years, they have become affordable for any do it yourselfer.

I purchased a Raytek MT6 online for less than $50. Full featured and mfg. by a great company. One of the best investments I've made in recent years to my toolbox. I like to point it directly at the thermostat housing for a reasonably accurate reading of the coolant temperature.

Cab heat is a byproduct of engine heat. Gotta get that engine coolant temp stabilized in the verified 200-210 range.

Then (assuming you don't have a heater core, heater control valve, blend door issue, etc), you should have good cab heat.

Good luck and let us know what you find!

gauge sender might be on the fritz, I know that doesn't explain the cabin heat but check it out anyway. you can verify the coolant temperature with infrared scanner on the thermostat housing.

While the advices given above is good you have to bear in mind one thing. The temperature displayed on the guage may not be the same as the engins temperature. You first have to verify the engine is coming up to 200 to 210 degrees. With a new thermostat (and I hope it is one from the Jeep dealer or at least one of the better ones offered at the discount auto parts store), there is no reason why it should not.

Assuming the engine is up to the proper temperature, it come time to trouble shoot the in-cab heat. This includes the heater core in the cab and all the vacumn operated valves to allow and direct the hot air to the area you desire. Start by checking the shut off valve in the engine that the hoses connect to. The hose layout is important. Also check that the valve opens when the heat is turned on and closes when the heat is turned off. Check this first by turning the heater control on and off and obsevring that the valve actually function properly. Again this valve should have 4 water hoses attached to it coming off the top of the engine and a vacumn line attached to the bottom. Someone with a Renix era XJ could help you to further diagnose the system.

As far as the heat is concerned... try flushing the heater core out, it may have a slight blockage. Make sure that your blend door is moving when you tell it you want hot air. An 87 should be cable operated and is visible by looking under the passenger side of the dash. You should see a lever with a metal rod attached to it that goes into a sleeve up to the heater controls. Also check your heater valve to make sure it is working, it is controlled by vacuum and if there is a leak, well you guessed it, it will not work and will not let hot water into the heater core..

If the engine IS coming up to heat and you are unsure of the heater coolant valve, the best thing to do, espcially in WI., is to just eliminate it. The later models don't have one anyway, and MANY poeple have just elimated it and replaced the junction with plumbing pieces for constant flow. This may also reduce crudding up of the heater core interior tubes.

magimerlin said:

As far as the heat is concerned... try flushing the heater core out, it may have a slight blockage. Make sure that your blend door is moving when you tell it you want hot air. An 87 should be cable operated and is visible by looking under the passenger side of the dash. You should see a lever with a metal rod attached to it that goes into a sleeve up to the heater controls. Also check your heater valve to make sure it is working, it is controlled by vacuum and if there is a leak, well you guessed it, it will not work and will not let hot water into the heater core..

Click to expand...

You are correct. The blend door/s are cable operated. However, the control valve for the hot water in the engine compartment is vacumn operated.

Winterbeater's advice is good. If you are unsure that the valve is operating pproperly, you could remove it and hook the hoses up directly. I did that on the ,94 I used to have when the valve broke (it is made of plastic with a useful life span of only that much).

Thanks for the help guys,

I checked to see if the valve was functioning properly and it seems to be when I move the temp knob from red to blue I can feel what little heat I have turn into absolutely no heat and I can also hear it make a slight sound like it is opening and closing. I talked to my uncle this morning(he's a jeep guru) and he said that my electric fan may be constantly on which would not allow the engine to ever properly heat up. Im going to go check on that here in a sec, and I will also check the heater core lines to see how warm they are. Another thing is that I think my intake manifold gasket might have a slight leak as the idle kind of drops down every once in a while and then picks itself up suddenly(my friends dad said he had this same problem on his cherokee) could this possibly be contributing to the heat issue? The jeep still runs fine and has great power but it just kinda stutters a little bit

A leaking intake manifold gasket would not hurt your heat, except for possible losing vacuum to move your coolant valve and mode (direction) doors. Your temp door (as stated) is cable controlled. I don't think it would cut heat much, but another consideration is whether your mechanical fan clutch is freewheeling properly. Try spinning it cold by hand.

But you need to focus first on whether your engine is getting hot enough or not.

I went and checked to see if the electric fan is on constantly and its not, I also checked my heater core lines and they both felt the same temperature and were warm, Im going to go check the sending unit wire to see if my gauge is faulty. The tech that worked on my jeep yesterday said that the cap on my overflow container seemed like it might be loosing pressure which could possibly be affecting heat?? but the overflow container and cap are brand new oem from the dealer so idk. I'll check back in in a bit.

I bought one of these off ebay (they're 30-40 locally)
http://cgi.ebay.com/ebaymotors/Pock...Z350278880110QQptZMotorsQ5fAutomotiveQ5fTools

Very handy for all sorts of things- definitely one of those "why didn't I get one sooner" gadgets.

Leaking cap should only cause overheating. Feel your engine. You can tell if it hot or not. If unsure, feel another engine that you know is getting hot enough for comparison.

You can search a little to find out about the closed system pressure bottle issues. 5-90 has posted a ton of stuff with his system battles. Short story: the cap is shit. A hose clamp around it can help. There is a better Volvo cap you can get. THe hood may hit on the cap too (not good).

But that is not why you are possibley running too cold.

Overflow is defineatly leaking air I put my ear up next to it and could hear the pressure hissing out. Is this supposed to happen?? Previous owner said when I bought the jeep that the heat worked great, and he also said that he had to replace the overflow tank because it cracked or something so this could be the possible cause maybe?

Does it leak air as soon as you start it up? Unfortuantaley, that can be an indication of a leaking head gasket. On most vehicle, then, the temp gage would swing quite a bit. And combustion gasses in the cooling system will not conduct heat to the heater core. If you open the bottle cap, can you see air bubbling up in the coolant?

Ill give that a try in a second

I grounded out the sending unit wire and turned the key and it didn't swing all the way it just stayed all the way down so it must have some wiring issue going on with it.

I started it up and listened for the air leak but i couldn't hear it over the engine/fan, I also let it run for a minute and removed the cap and looked in the tank and didn't see any bubbling looked like it was functioning normal. Last time I checked a few days ago my oil looked normal not sure how jeeps react with a blown hg but the oil didnt look like chocolate milk.

When I start the jeep as its cranking over my temp gauge swings all the way to the right(when its plugged into the temp sensor) and then settles back down after the engine starts is this normal? looks like all the other gauges pretty much stay put until the engine is running. sorry for all the questions im a jeep noob.

The gage sounds normal. I would focus first on whether the engine is getting hot enough or not. You don't rally need a thermometer for that, even though it would be useful. Doesn't someone else around have a car or truck that is putting out good heat? Start them both up and let them run for 15 or 20 minutes. Then carefully try to put your hand on your motor and compare it to the other motor that the heater works good in. Then proceed to feel the radiator and heater hoses.

If yours is overall colder, try running it a while longer with cardboard over the radiator and see if that helps.