My engine won't heat up enough for the heater to warm up in the cab of the 1998 Ford Ranger 4 cyl. I have been running with cardboard in front of radiator, but not helping much. Replaced thermostat last night, but still only a trace of heat output. Upper radiator hose only gets "comfortably warm" to the hand, and does not build up pressure inside it. Why won't the engine warm up?


Asked by Nov 26, 2014 at 01:47 PM about the 1998 Ford Ranger XLT Extended Cab SB

Question type: Maintenance & Repair

New thermostat, new antifreeze, cardboard still in front of radiator, and temperature indicator still doesn't come up!

15 Answers


Sounds like someone put water instead of coolant in the radiator and now you have rust blocking the heater. Remove the 2 hoses at the Firewall that go the the heater .... now at a very low water pressure ... do not over pressure or you may damage the heater cor ... now try to back flush the heater core ... be careful because when it clears the blockage ... it fly's out like a shotgun blast ... refill with coolant and get a good waterpump anti-rust additive

5 people found this helpful.

Thanks, but why (and how) would heater core blockage keep the engine from warming up? The radiator tank and upper radiator hose SHOULD get warm enough that they would be uncomfortable to take hold of with even a 180 degree thermostat, let alone a 192. Why won't the engine warm up and get the coolant hot?

6 people found this helpful.

Geez ... Usually just the opposite is true ... The engine gets too hot. Read this thread and good luck ~~ I mean ... you have close to 1200 F at the exhaust manifold and yet the engine heat doesn't seem to be transferring to the water. You are contradicting the rules of Thermodynamics ... and of course that's not possible

4 people found this helpful.

Did you come to a solution for this problem ? I'm going through the same thing 98 ranger 2.5. New water pump new t stat new antifreeze and just did a head gasket new temp sensors. engine won't warm up any suggestions ?

6 people found this helpful.

have you replaced your thermostat?

1 people found this helpful.

I am having the exact same issue in my 00 Ranger with a 2.5L. I am starting to think that as the engine block ages with coolant in it that rust is corroding the metal inside and allowing the coolant to get closer than normal to the exterior cylinder walls which is exracting heat too effeciently. Just my theory but I can't think of anything else. I have checked and rechecked everything. I have worked on cars my whole life and never seen anything quite like it. I drove mine earlier today and i drove for 45 minutes without my truck overheating even without a radiator cap and only 1/2 the coolant required. It seems to be an air cooled engine, Ford just never realized it!

8 people found this helpful.

did anyone figure this out i got same problem 96 ranger 3.0

Having a similar issue. Garage said new Thermostat was needed. Changed that but threw unfortunate incident, I forgot the O-ring on the the first install. Truck overheated and stopped blowing hot air. Re-set the Thermostat with the O-ring and it still overheated/blew cold until, all of a sudden, it whined and started clicking. Truck cooled down and the heater blew warm. For about 10 minutes. Diagnosed a bad actuator. Replaced that. Still no heat. Confirmed the blend door functions. Still no heat. Not sure what it could be. 2005 Ford Ranger 4.0 V6 4x4. Looking for help.


If you at any time used water or a radiator leak stop agent than the 2 hose's going through the firewall could be restricted ... remove both hoses and gently purge them out until you get a nice flow ... DO NOT USE A FULL PRESSURE HOSE OR YOU MAY DAMAGE THE HEATER CORE

1 people found this helpful.

New radiator cap

1 people found this helpful.

I figured it out, why the ford Ranger wont build enough heat, wont warm up enough to drop off high idle, and in my case, triggered the code for the Cat and I could not get it to pass inspection in my state. It is in fact a problem is with the thermostat. You have to put a spacer, I used an o-ring to putting it behind the state rubber itself. Its easy to test, remover the top radiator hose from the radiator and the heater hose that goes to the thermostat housing. After draining some fluid out, put your finger over the heater hose port and plow into the radiator hose. If the thermostat is closed and sealed, you wont be able to blow through it--- But there you will find the problem. Replace with a higher quality state, State or Napa. With the housing in hand and the stat installed holding it in place. Blow through it to see if it seals, then make sure the little ears stick out enough so that when installed, those ears will keep pressure on the state with a good seal.

1 people found this helpful.

Here is the O-ring


Here is how to test it, blow into the radiator hose to see if it leaks?


Here is how to test it, With the photo


Appreciated seeing the answer ! I posted my question 11/26/14, and since had back-flushed heater core and replaced thermostat, to no avail. Still very little heat, clear up unto 12/24/18, when I hit an icy curve and rolled the truck, but thanks for solving the mystery. It looks like others had the same problem.

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