Lukewarm heat in 96 gc (4.0l)

[SLATERNY]

Recently had my radiator and water pump (along with pulleys/belts) replaced, and it seems that since then, my heat does not get "hot"...best it gets is maybe "lukewarm"...i noticed that my temp gage even when i am fully warmed up, never reaches the center of the gage, where i am pretty sure it used to before...could that be why my heat isn't hot anymore?
I should mention that it was like that before the water pump was replaced, and the mechanic was hoping that it was related to the deteriorating water pump...but it wasnt. He said it maye be the heater core, which is a very expensive job for the grand c's.

I live in the northeast, and it is, and has been, brutally cold!

Help!

[hardisk_c]

As a member from the Dakotas (currently -16 according to weather chan) I can appreciate that it takes a bit more for the temp needle to get up to normal, even after 20 minutes running/driving this evening, mine was only hovering around the 1/3 level, but properly warmed up, it does tend to hover just under the half mark.

Question: in replacing the pump and radiator assemblies was the thermostat replaced?

I wonder if someone inadvertantly (or purposefully with the best of intentions) replaced the thermostat with one w/ a lower temp rating. Haynes Manual for my 94 (which says it covers 93 up til 04) states a 195 degree thermostat should be used on the 4.0 engine. If a lower-temp thermostat was used, say a 165, it will open prematurely, and the engine won't get to full temp, costing you heat at the vents.
If your work sheet from the shop shows the thermostat being replaced, see if you can post the part # up on the forums and/or google the part number and see what the temperature rating is at before dissecting that upper coolant mount to get at the t-stat again.

If the t-stat was not replaced, now may be the time to have that done before condemning the heater core. A worn t-stat can stay open ALLLLL the time, and therefor, in colder weather, never truly let the engine get up to temp before running coolant through the radiator, nor will it shut down flow to the radiator if the coolant temp is too cool. Last winter the t-stat on my '94 finally wore out, leaving it in the open position, and while I couldn't tell you what the temp gage was like (broken temp sensor at the time, no reading @ the console) I can definately tell you that a 'lukewarm' heater was definately one of the symptoms. One thing that may give a bit of a boost to the system is to put something in front of the grill, like a piece of cardboard zip-tied to the grill. If doing that gives the heater a bump, there's probably something @ issue with the thermostat side of the connection, rather than the heater core.

Anyways, I've more than put my in. Let me know if this helps.

[SLATERNY]

well, it turns out that it was the thermostat...it was a 180dg one, and it appeared to be stuck open...swapped with a 195, and the temp gage is dead center on the temp gauge, and the heat is all good...
Boy, am I glad it wasn't the heater core!