# Heating up **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [February 8, 2008, 4:45pm UTC](https://community.cartalk.com/t/heating-up/10361 "2008-02-08T16:45:18Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![mikeb428](https://avatars.discourse-cdn.com/v4/letter/m/f17d59/32.png) [@mikeb428](https://community.cartalk.com/u/mikeb428)\ **Post date:** [February 8, 2008, 4:45pm UTC](https://community.cartalk.com/t/heating-up/10361/1 "2008-02-08T16:45:18Z")
I HAVE A 1986 TOYOTA PICK UP TRUCK 2 WHEEL DRIVE 22R ENGINE. WHEN I START IT AND DRIVE THE TEMPERATURE GOES ALMOST TO THE HOT ON THE GAUGE STAY THERE FOR ABOUT A MINUTE THEN DROP DOWN TO OPERATING TEMP AND STAY THERE AS LONG AS YOU DRIVE. I HAVE REPLACED THE THERMOSTAT TWICE,FLUSHED OUT THE SYSTEM ---
**Author:** ![MikeInNH](https://avatars.discourse-cdn.com/v4/letter/m/a587f6/32.png) [@MikeInNH](https://community.cartalk.com/u/MikeInNH)\ **Post date:** [February 8, 2008, 5:01pm UTC](https://community.cartalk.com/t/heating-up/10361/2 "2008-02-08T17:01:44Z")
Could be just a faulty temp switch. Try replacing that. ---
**Author:** ![mikeb428](https://avatars.discourse-cdn.com/v4/letter/m/f17d59/32.png) [@mikeb428](https://community.cartalk.com/u/mikeb428)\ **Post date:** [February 8, 2008, 7:16pm UTC](https://community.cartalk.com/t/heating-up/10361/3 "2008-02-08T19:16:49Z")
when it overheats and I stop the water in the radiator is boiling. Thanks for any ideas ---
**Author:** ![VDCdriver](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/vdcdriver/32/30_2.png) [@VDCdriver](https://community.cartalk.com/u/VDCdriver)\ **Post date:** [February 8, 2008, 7:21pm UTC](https://community.cartalk.com/t/heating-up/10361/4 "2008-02-08T19:21:30Z")
Well, if you are using water, rather than antifreeze/coolant, that might be part of the problem. Since the system was designed for the higher boiling point of a 50/50 coolant/water mix, that would be a logical place to start. Also, a defective radiator cap can allow the liquid in your radiator to boil more easily than if the cap is working properly. Try replacing the cap after you drain the water and replace it with the proper 50/50 coolant/water mix. ---
**Author:** ![bing](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/bing/32/4619_2.png) [@bing](https://community.cartalk.com/u/bing)\ **Post date:** [February 8, 2008, 8:09pm UTC](https://community.cartalk.com/t/heating-up/10361/5 "2008-02-08T20:09:12Z")
You also could have air in the system yet if you replaced the thermostat. Some cars have a bleed valve that needs to be opened to fully bleed the air out of the system. The air bubble blocks the coolant flow until enough pressure builds up to overcome the air bubble. Same as a head gasket symptom except stays cool after the first overheating instead of cycling up and down. ---
**Author:** ![Joseph\_E\_Meehan](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/joseph_e_meehan/32/21_2.png) [@Joseph\_E\_Meehan](https://community.cartalk.com/u/Joseph_E_Meehan)\ **Post date:** [February 8, 2008, 8:39pm UTC](https://community.cartalk.com/t/heating-up/10361/6 "2008-02-08T20:39:51Z")
Air in the system can cause that. I assume you are not using water in the radiator (water in the radiator is boiling) but rather coolant, possibly mixed with water. ---
**Author:** ![hellokit](https://avatars.discourse-cdn.com/v4/letter/h/6a8cbe/32.png) [@hellokit](https://community.cartalk.com/u/hellokit)\ **Post date:** [February 8, 2008, 10:18pm UTC](https://community.cartalk.com/t/heating-up/10361/7 "2008-02-08T22:18:19Z")
You say, “…when I stop, the water in the radiator is boiling”. Explain. All engines have pressurized cooling systems. Their NORMAL operating temperatures (about 220F - 230F degrees) are above boiling for UNPRESSURIZED coolant (which is 212F degrees). Pressurized systems can run up to about 260F degrees before boil-over. IF you took the radiator cap off an engine that is at its normal operating temperature (say, 220F degrees), it WOULD boil over. The temperature that the thermostat opens (180F to 195F degrees) is only the temperature that the coolant is diverted to the radiator. If a radiator is boiling over, and the engine temperature is normal, the radiator cap is probably defective. In that case, new radiator cap installed, problem solved. ---
**Author:** ![pleasedodgevan](https://avatars.discourse-cdn.com/v4/letter/p/51bf81/32.png) [@pleasedodgevan](https://community.cartalk.com/u/pleasedodgevan)\ **Post date:** [February 8, 2008, 10:23pm UTC](https://community.cartalk.com/t/heating-up/10361/8 "2008-02-08T22:23:25Z")
Your truck is also old enough to need a new radiator if you have the original one stil in there. It may not be causing the trouble now but it will get around to it. See if the fins are starting to rot away. From the back with the shroud pulled back, you should see some funny colors and too much of the tubes showing. 5% to 10% gone is too much.