low engine temp

[J B Cuz]

I have an 87 2.5l 5spd 4x4.The engine temp is around 140 deg according to the gauge and an infra red tester. Needless to say the computer will not go into closed loop and my milage sucks. When I started the build I ran radiator cleaner the the system to clean every thing up. I have replaced the radiator water pump the t stat (twice thought ((one NAPA one stant)) I had a bad one. runs the same as the first) and all the hoses.

 

I am at a loss as to what could be going on?

 

J B Cuz

[Oizarod115]

need to know where yuo're checking the temperature at with the thermometer, and maybe try checking another motor to see if the gun seems accurate.

 

its likely if both sources say the same thing then it is actually cold, try a thermostat from the dealer.

 

and make sure you're getting either a 185 or a 195 degree thermostat. something in that range is good for a 4.0L

[jmderyke]

I am also having the same problem here's my findings. (some of these may not be your problem) First run oem thermostat 195 degree. the thermostat on jeeps open slower than other cars because it get bypassed to the heater core and radiator right at thermostat housing, if you have a 180 degree or lower it will open too soon and close early never get to operating temperature.

Assuming your 87 is the same as my 86 there are two temperature sensors, one is for the ecu and the other is for gauge. sounds like the one for your gauge is accurate, the other might be on the intake manifold drivers side, on the side of the manifold not on top (one on top is air flow meter) this one controls your ecu. if this is off it will constantly be telling your ecu that engine is very cold resulting in rich air fuel mixture making it hard for engine to reach operating temp.

 

Check your spark plugs for incomplete combustion this will be all black all around electrode and insulator. You want coco brown color. If this is the case your air/ fuel mixture is off or incorrect heat range of the plug. Incorrect heat range happens often due to jackass behind counter giving someone high performance plugs that has lower heat range instead of stock heat range or you live in cold area and may require hotter plug.

 

hope this helps

[beaterjeep]

Could it possibly be a blocked heater core? I honestly have no idea here, just tossing out ideas really.

[HOrnbrod]

Low engine temp in both the 2.5 and 4.0 engines is nearly always caused by an defective aftermarket "offshore" manufactured thermostat. Go to the dealer and pick up the correct OEM 195-degree stat. In your case the one you need is p/n 83501426AC , about $10. This is not something to cheap out on. :D

[J B Cuz]

I have used the IR to check in multipal places, t stat housing heater core inlet, at t he temp sender on the block, at the temp sender on the manifold computer input, they all check around 140. checked another truck TJ and it showed 200 at the t stat. I also check it against boiling water @ 225 deg. I will try the factory t stat.

 

Thanks J B Cuz

[J B Cuz]

installed the jeep stat and there is no change in the engine temp. There are differances in the construction. The jeep stat has a small bleed hole in it.

 

J B Cuz

[Eagle]

Try blocking off half or two-thirds of the radiator with heavy cardboard and see if that makes a difference. Connecticut doesn't get nearly as cold as where you are, but even around here a lot of trucks and school buses run grille jackets in the winter and keep them buttoned up most of the way.

[HOrnbrod]

How's your heater working? Are you getting good heat output?

[jmderyke]

o yeah i forgot....2.5 have the worst fan clutches in the world they freeze up and make the fan run all the time. I ripped mine off a while ago and put a electric fan on.

I forgot about that trick Eagle nice!

[J B Cuz]

I covered the radiator with cardboard and the temp stays the same. Heater output is OK but not great. I am trying to find someone local that has a real time code reader for the renix, this way I could see what temp the computer thinks it is.

 

J B Cuz

[J B Cuz]

I got the code reader today and the computer is seeing 192 deg and the gauge still show 160. The IR reader is still showing 160 also but I hav :dunno: e been told that reading though the metal will change the temp. The good part is the computer is reading correct, the bad part is my mileage still sucks and is was barking up the wrong tree. Back the the manuals.

 

J B Cuz

[Eagle]

Poor fuel mileage can be the oxygen sensor. If it's not reading correctly, it may be calling for the injector (singular because this is a TBI 4-cyl) to squirt more juice than what the engine needs to maintain the optimum air/fuel mixture. Last time I replaced it on my '88 4.0L, I knoew it was due because when I would take my foot off the gas to shift (5-speed) I would hear a muffled "POP" from under the floor. That was a small backfire in the catalytic converter, caused by raw fuel that was NOT being burned because the O2 sensor wasn't reacting to the change in engine conditions quick enough when I dumped the throttle and disengaged the clutch.

 

How old is your O2 sensor?