Thermostat keeps locking shut!

[ChevySepticGuy]

Hello Guys,

My old Chevy is having a problem with the thermostat. In the past 5 months I've put three thermostats on her!

They just keep locking shut!

I'm wondering if it has anything to do with the job she is doing, because she pumps the septic tanks from the Manifold vacuum source.

When i open the ball valve on the tank of the truck the engine changes idle and begins to pump. Obviously she will run a bit hotter. I think this trigger the theromstat to shut.

I even tried put a winter thermostat on her (190 degrees) and it still locked!

Any ideas guys?

The few days the thermostat works are great ! Lots of nice warm heat!...Then when she locks it's very minimal heat, but still enough to keep your toes from freezing!


Thank a lot! & Happy Holidays!

"Chevy Septic Guy"
1985 Chevrolet Custom Deluxe C30 (1 ton) 350.

[VileZambonie]

A stuck closed thermostat will cause the engine to overheat not give you poor heat. Your heater core is probably plugged. And how the devil do you pump a septic system out with your intake manifold?!  

[ChevySepticGuy]

I'll guess i'll have to flush the heater core. I hope it's not too big of a job.

My truck was running hot for most of the summer and fall, so this is probably all related. Any quick tips on flushing the heater core?

Yep, I know it sounds crazy, but the truck will pump a septic tank! there is a 500 gal tank on the back of the truck. A 1/2 line runs from the man. vac. source and runs to a ball valve on top of the tank on the back. after a few seconds enough suction will build up in the tank to pump out of a 2 1/2 inch suction hose at the back, and then were pumpin'!

Thanks for the help!  

[Redneckchevy]

I belive it ...U get an air tight tank suck the air out with a small vac source ...Then when u open the valve the air wants to be sucked into the tank any way it can ...so what ever is in front of the house gets sucked in .....And yea i would check heater core....Did u take the thermastat out and let it kool and then drop it in boiling water? its a redneck thing but it will show ya somting....if u still have doubts in ur mind bout it ..

[Lt.Del]

Get a different brand thermostadt and be sure to put the spring side down towards the intake.  

If both of your core hoses are warm after engine warms up, i really dont think you need to flush core, but it doesnt hurt to.  Both line warm means the antifreeze is freely going in and out of the core.

but to flush, just unhook the hoses from the engine and get some clamps.  get some copper tubing, about three inches  and clamp an old washing machine hose (end cut off) to the core hose.  Twist the other endd of the washing machine hose onto your garden hose.  Ensure the other hose of the core is pointing in a safe direction and let the h2o fly.

SgtDel
aka "Andy"

www.delbridge.net

1979 Big 10 383 stroker
1991 Blu 'Burb 3/4 ton 4x4

[ChevySepticGuy]

Thanks for the input guys really appreciate it!

Theres nothing worse than a broken down truck when it comes to putting food on your table.

I love these old trucks though. It's actually my 3rd 73-87 chevy.

Even though I may not have to, I'll flush my heater core anyway and put a new stat in. It's funny the last one I bought (at Canadaian tire...eh!...lol  ) was their brand called "failsafe" I was hoping it would work, but i'll try getting number 4 some other place...urg...this get frustraiting after a while!

Thanks again guys!

Happy holidays!

"Chevy Septic Guy"
1985 Chevrolet Custom Deluxe C30 (1 ton) 350.