# Leaking thermostat and boiling reservoir **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** mustang, ford\ **Created:** [July 10, 2018, 10:20pm UTC](https://community.cartalk.com/t/leaking-thermostat-and-boiling-reservoir/120791 "2018-07-10T22:20:02Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Matthew\_Johnson](https://avatars.discourse-cdn.com/v4/letter/m/3bc359/32.png) [@Matthew\_Johnson](https://community.cartalk.com/u/Matthew_Johnson)\ **Post date:** [July 10, 2018, 10:20pm UTC](https://community.cartalk.com/t/leaking-thermostat-and-boiling-reservoir/120791/1 "2018-07-10T22:20:02Z")
I have a 98 mustang. It has been having best issues for a while and a boiling reservoir. The thermostat is brand new as I replaced it last night. Car ran fine this morning but it overheated when I got off work and was driving home. The reservoir has a hole in the top corner of it and may have something to do with it, and the thermostat has leaked some liquid. I couldn’t see the color so I’m not sure what liquid it could be. What could be causing this? Also has a new radiator and I’m not sure if the fan even turns on. I haven’t checked that. ---
**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:** [July 10, 2018, 10:23pm UTC](https://community.cartalk.com/t/leaking-thermostat-and-boiling-reservoir/120791/2 "2018-07-10T22:23:59Z")
If the cooling system has a leak, it can’t hold pressure. And the engine can overheat. Tester ---
**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:** [July 10, 2018, 10:29pm UTC](https://community.cartalk.com/t/leaking-thermostat-and-boiling-reservoir/120791/3 "2018-07-10T22:29:53Z")
> [@Matthew\_Johnson](#): > > The reservoir has a hole in the top corner of it > [@Tester](#): > > If the cooling system has a leak, it can’t hold pressure. And the engine can overheat. Tester has provided the answer for the OP. ---
**Author:** ![Matthew\_Johnson](https://avatars.discourse-cdn.com/v4/letter/m/3bc359/32.png) [@Matthew\_Johnson](https://community.cartalk.com/u/Matthew_Johnson)\ **Post date:** [July 10, 2018, 10:34pm UTC](https://community.cartalk.com/t/leaking-thermostat-and-boiling-reservoir/120791/4 "2018-07-10T22:34:18Z")
Im not sure where the leak could be though. I replaced the thermostat last night and its now leaking. It hasn’t leaked much, but it didn’t leak with the old one but does with the new one. ---
**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:** [July 10, 2018, 10:36pm UTC](https://community.cartalk.com/t/leaking-thermostat-and-boiling-reservoir/120791/5 "2018-07-10T22:36:33Z")
> [@Matthew\_Johnson](#): > > I replaced the thermostat last night and its now leaking. That’s where the coolant leak is. Tester ---
**Author:** ![insightful](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/insightful/32/2732_2.png) [@insightful](https://community.cartalk.com/u/insightful)\ **Post date:** [July 10, 2018, 11:01pm UTC](https://community.cartalk.com/t/leaking-thermostat-and-boiling-reservoir/120791/6 "2018-07-10T23:01:38Z")
Do you have the V6 (unpressurized reservoir): ![MustangV6](https://global.discourse-cdn.com/cartalk/original/2X/6/64219f809ba86a9f55ce7e3ccb454dbe730d209f.png) Or the V8 (pressurized reservoir)?: ![MustangV8](https://global.discourse-cdn.com/cartalk/original/2X/0/0d26b76034b149aac60d36f99b812143ede88db1.png) ---
**Author:** ![Matthew\_Johnson](https://avatars.discourse-cdn.com/v4/letter/m/3bc359/32.png) [@Matthew\_Johnson](https://community.cartalk.com/u/Matthew_Johnson)\ **Post date:** [July 10, 2018, 11:08pm UTC](https://community.cartalk.com/t/leaking-thermostat-and-boiling-reservoir/120791/7 "2018-07-10T23:08:31Z")
I have the v6 ---
**Author:** ![insightful](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/insightful/32/2732_2.png) [@insightful](https://community.cartalk.com/u/insightful)\ **Post date:** [July 10, 2018, 11:10pm UTC](https://community.cartalk.com/t/leaking-thermostat-and-boiling-reservoir/120791/8 "2018-07-10T23:10:46Z")
> [@Matthew\_Johnson](#): > > I have the v6 “Boiling” in an unpressurized reservoir is many times caused by a blown head gasket. Try a new radiator cap…and pray… ;-] ---
**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:** [July 11, 2018, 2:53am UTC](https://community.cartalk.com/t/leaking-thermostat-and-boiling-reservoir/120791/9 "2018-07-11T02:53:16Z")
I presume you mean the thermostat housing is leaking. When you buy a replacement thermostat, you also have to buy a new gasket that fits the housing. The gasket doesn’t come with the thermostat automatically. Did you do that?