# Temp gauge fluctuates a little **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** ford, ranger\ **Created:** [January 19, 2018, 12:25am UTC](https://community.cartalk.com/t/temp-gauge-fluctuates-a-little/111458 "2018-01-19T00:25:16Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Wesley\_Gaynor](https://avatars.discourse-cdn.com/v4/letter/w/3ab097/32.png) [@Wesley\_Gaynor](https://community.cartalk.com/u/Wesley_Gaynor)\ **Post date:** [January 19, 2018, 12:25am UTC](https://community.cartalk.com/t/temp-gauge-fluctuates-a-little/111458/1 "2018-01-19T00:25:16Z")
I have a 1991 ranger 2.9liter xlt 4x4with 77k original miles. I blew a headgasket and replaced it. Also flushed the radiator, replaced 2 temp sensors, thermostat, tps, and iac. The temp gauge was fluctuating up and down and getting too hot. I checked the wires on sending unit and they work. I replaced the thermostat again and its better, but still the gauge goes up and down a little. Is this normal? ---
**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\ **Post date:** [January 19, 2018, 12:52am UTC](https://community.cartalk.com/t/temp-gauge-fluctuates-a-little/111458/2 "2018-01-19T00:52:11Z")
It is if you still have air in the system. Did you turn the heater on when you bled the system? Did you test the radiator cap? Now the less optimistic thoughts: Did you run a leakdown test to ensure that the cylinders were sealed? Did you check the head for flatness (warpage) when you did the head gasket? id you ensure that the surface of the block was flat and free of eroded passages that might allow passage after the head gasket replacement? Did you clean it completely? ---
**Author:** ![Wesley\_Gaynor](https://avatars.discourse-cdn.com/v4/letter/w/3ab097/32.png) [@Wesley\_Gaynor](https://community.cartalk.com/u/Wesley_Gaynor)\ **Post date:** [January 19, 2018, 12:58am UTC](https://community.cartalk.com/t/temp-gauge-fluctuates-a-little/111458/3 "2018-01-19T00:58:34Z")
Heads were shaves. Leak down test was good. New radiator cap. Heat was on when burping the radiator. Block was good and cleaned properly. Maybe i need to burp it again. ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [January 19, 2018, 1:02am UTC](https://community.cartalk.com/t/temp-gauge-fluctuates-a-little/111458/4 "2018-01-19T01:02:54Z")
There’s probably air trapped in the cooling system. Try this. Get the engine up to operating temperature. While the engine is idling, loosen the upper radiator hose clamp and slip a small flat bladed screwdriver between the upper radiator hose and the hose neck on the radiator. Allow the engine to idle until all the air is purged out and nothing but coolant comes out. Remove the screwdriver and tighten the hose clamp. Tester ---
**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\ **Post date:** [January 19, 2018, 1:10am UTC](https://community.cartalk.com/t/temp-gauge-fluctuates-a-little/111458/5 "2018-01-19T01:10:12Z")
Sounds like you did a thorough job. I tip my hat to you. Perhaps if another burp doesn’t work, a good radiator testing/mapping/boiling is in order. One other possibility comes to mind. Radiator and heater hoses are a sheath over a rubber lining. Sometimes when an engine is overheated (or even as a root cause) the inner liner can collapse when hot and block the coolant. Heater hose and radiator hose is cheap. It might be prudent to change it out. ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [January 19, 2018, 3:03am UTC](https://community.cartalk.com/t/temp-gauge-fluctuates-a-little/111458/6 "2018-01-19T03:03:19Z")
Once the coolant reaches a stable temperature on all my vehicles it usually stays there pretty steady. But there are exceptions. Long uphills might cause the coolant temp to slowly rise, and if it is really cold outside it might drop , especially when going faster. My guess, air remains in the cooling system. Do what Tester says above, but before you start drive the front wheels up on ramps. That will improve your odds. If that doesn’t fix it, other ideas … - pressure test the cooling system including the radiator cap - water pump is faulty or debris is blocking the inlet or outlet - make sure the radiator fan is spinning when it should and at the correct rpm ---
**Author:** ![Eddie123](https://avatars.discourse-cdn.com/v4/letter/e/bbce88/32.png) [@Eddie123](https://community.cartalk.com/u/Eddie123)\ **Post date:** [January 19, 2018, 5:26pm UTC](https://community.cartalk.com/t/temp-gauge-fluctuates-a-little/111458/7 "2018-01-19T17:26:40Z")
I don’t know if it is relevant but I disconnected the heater in my '97 ranger (we live in Texas and really don’t need a heater) by simply plugging the hoses. This caused the gauge to go up and down, even when driving. I replaced the plugs with a loop which allowed the water to return and it fixed the problem. ---
**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\ **Post date:** [January 19, 2018, 8:05pm UTC](https://community.cartalk.com/t/temp-gauge-fluctuates-a-little/111458/8 "2018-01-19T20:05:51Z")
> [@Eddie123](#): > > I don’t know if it is relevant It is relevant. It suggests that a plugged heater hose or heater core can cause engine temp to fluctuate. Until the problem is solved, information like this could be the key to the solution. ---
**Author:** ![Eddie123](https://avatars.discourse-cdn.com/v4/letter/e/bbce88/32.png) [@Eddie123](https://community.cartalk.com/u/Eddie123)\ **Post date:** [January 19, 2018, 8:22pm UTC](https://community.cartalk.com/t/temp-gauge-fluctuates-a-little/111458/9 "2018-01-19T20:22:26Z")
I agree, it was the fluctuating temp that caught my eye. An obstruction in the heater line might do the same thing. ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [January 19, 2018, 11:31pm UTC](https://community.cartalk.com/t/temp-gauge-fluctuates-a-little/111458/10 "2018-01-19T23:31:38Z")
> [@Eddie123](#): > > I don’t know if it is relevant but I disconnected the heater in my '97 ranger (we live in Texas and really don’t need a heater) by simply plugging the hoses. This caused the gauge to go up and down, even when driving. I replaced the plugs with a loop which allowed the water to return and it fixed the problem. I’m surprised that the lack of flow through the heater core could affect the engine’s cooling system. I suppose if the engine cooling system performance was marginal to begin with, the heater core could act as a helper radiator to keep the engine cooled. Maybe that’s the explanation. But that would only work in winter when the heat mode is selected. How does the Ranger regulate the inside temperature then when you don’t want any heat? On all the vehicles I’ve owned it’s done by blocking off the coolant flow to the heater. Perhaps on the Ranger the heat selection done with the vent doors, and a full flow of coolant always flows through the heater core even when no heat is selected. I guess the cooling system currents could be affected throughout if the flow through the heater core was block off, as the system wasn’t designed or tested for that. ---
**Author:** ![Rod-Knox](https://avatars.discourse-cdn.com/v4/letter/r/a183cd/32.png) [@Rod-Knox](https://community.cartalk.com/u/Rod-Knox)\ **Post date:** [January 20, 2018, 12:39am UTC](https://community.cartalk.com/t/temp-gauge-fluctuates-a-little/111458/11 "2018-01-20T00:39:04Z")
My 2000 Ranger has a heater shut off valve on the coolant hose but there is a 3/8" bypass hose that makes virtually the same connections.The bypass is very convenient for burping the engine. ---
**Author:** ![Eddie123](https://avatars.discourse-cdn.com/v4/letter/e/bbce88/32.png) [@Eddie123](https://community.cartalk.com/u/Eddie123)\ **Post date:** [January 20, 2018, 1:11am UTC](https://community.cartalk.com/t/temp-gauge-fluctuates-a-little/111458/12 "2018-01-20T01:11:58Z")
It was very sensitive to outside temperature. When it was warm to hot (80-100F) outside the gauge would register as you would expect but, when it was cooler (60F or so) even driving down the street the gauge would go from normal to cool and then back up. As I sat at a red light it would change and then go back up. When I was at highway speed it would drop and go back to normal. It did not cycle up-to-down-to-up with any regularity. It seemed to come out of the blue but was fairly frequent on any trip. It was always multiple cycles. I asked a mechanic about this and he shook his head but thought it might have something to do with the flow of the water to the heater coils. I put in the loop which bypassed the heater coils (instead of just stopping it going to the coils at all) and just returned the water to the radiator and everything has worked well since then. To me, a couple feet of insulated hose should have made no difference but it seems to have made all the difference. The other interesting point is how sensitive it was to outside temperatures. When it all settled out, I decided not to look this gift horse too closely in the mouth since I really never use the heater anyway. ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [January 20, 2018, 1:22am UTC](https://community.cartalk.com/t/temp-gauge-fluctuates-a-little/111458/13 "2018-01-20T01:22:01Z")
It’s a great diagnostic test, but might not work as a solution for the OP as they may live in a colder area and need the heater to work. ---
**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\ **Post date:** [January 20, 2018, 1:42am UTC](https://community.cartalk.com/t/temp-gauge-fluctuates-a-little/111458/14 "2018-01-20T01:42:16Z")
> [@George\_San\_Jose1](#): > > On all the vehicles I’ve owned it’s done by blocking off the coolant flow to the heater. It may be that they blocked the path to the heater core and diverted the flow back to the engine, bypassing the heater core. That would be the normal way. The poster that offered the thought blocked the lines without diverting the flow. I believe it’s wise not to disallow any possible explanation until it’s been tested. Too many times over the years I’ve been running tests and had the system(s) under test react in ways I hadn’t expected. Until the solution is found and confirmed Id’ welcome all ideas. That’s how I learn. ---
**Author:** ![Wesley\_Gaynor](https://avatars.discourse-cdn.com/v4/letter/w/3ab097/32.png) [@Wesley\_Gaynor](https://community.cartalk.com/u/Wesley_Gaynor)\ **Post date:** [January 20, 2018, 1:52am UTC](https://community.cartalk.com/t/temp-gauge-fluctuates-a-little/111458/15 "2018-01-20T01:52:29Z")
Thanks for all the help! Im going to start with the cheapest and easiest…i will burp the radiator again. Second step will be the hoses. Bypassing the heater core is a no-go. I live in kentucky…it was 1 degree outside the other day! ---
**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\ **Post date:** [January 20, 2018, 2:10am UTC](https://community.cartalk.com/t/temp-gauge-fluctuates-a-little/111458/16 "2018-01-20T02:10:21Z")
> [@Wesley\_Gaynor](#): > > it was 1 degree > > outside the other day! LOL, Must be nice to be in a temperate zone… I’m in New Hampshire! 😬 ---
**Author:** ![Wesley\_Gaynor](https://avatars.discourse-cdn.com/v4/letter/w/3ab097/32.png) [@Wesley\_Gaynor](https://community.cartalk.com/u/Wesley_Gaynor)\ **Post date:** [January 20, 2018, 2:11am UTC](https://community.cartalk.com/t/temp-gauge-fluctuates-a-little/111458/17 "2018-01-20T02:11:45Z")
You can keep that cold weather. I like it around 80 degrees ---
**Author:** ![Renegade](https://avatars.discourse-cdn.com/v4/letter/r/b4bc9f/32.png) [@Renegade](https://community.cartalk.com/u/Renegade)\ **Post date:** [January 20, 2018, 2:21am UTC](https://community.cartalk.com/t/temp-gauge-fluctuates-a-little/111458/18 "2018-01-20T02:21:51Z")
What ever happened to global warming it was down to 7 here 2 night’s ago. ---
**Author:** ![Wesley\_Gaynor](https://avatars.discourse-cdn.com/v4/letter/w/3ab097/32.png) [@Wesley\_Gaynor](https://community.cartalk.com/u/Wesley_Gaynor)\ **Post date:** [January 20, 2018, 12:11pm UTC](https://community.cartalk.com/t/temp-gauge-fluctuates-a-little/111458/19 "2018-01-20T12:11:38Z")
Rod\_Knox, I wish mine had one, but sadly,…it doesn’t. I have a steep grade I can park it on, so hopefully I can burp it there and fix it. ---
**Author:** ![PvtPublic](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/pvtpublic/32/13089_2.png) [@PvtPublic](https://community.cartalk.com/u/PvtPublic)\ **Post date:** [January 20, 2018, 12:39pm UTC](https://community.cartalk.com/t/temp-gauge-fluctuates-a-little/111458/20 "2018-01-20T12:39:17Z")
> [@Renegade](#): > > What ever happened to global warming it was down to 7 here 2 night’s ago. I thought these wild temp swings were evidence of global warming. [Next page](https://community.cartalk.com/t/temp-gauge-fluctuates-a-little/111458.md?page=2)