Engine temp up and down WTF

[supramad77]

Guys i have been having some problems with my motor the last couple of weeks. It has been dumping water out periodicly and the temperature guage is going up and down like mad. There does not seem to be any blockages in the rad. Am i looking at BHG?
The car runs pretty good but is a little rough when cold.
Yesterday the temp guage was right up flashing and then the next second it was normal and stayed like that for the rest of the drive. WTF
Help Please.

[Moorman]

Last weekend I was seeing the same. Fan clutch was only *sometimes* engaging, so it'd start to heat up, then the fan would spin up and temps would shoot back to normal. This would repeat randomly. Replace that fan clutch & I bet you'll be back to normal.

[Dangerous Ken]

Pat,

To find out for sure it's not a BHG, get a test kit for BHGs.
Snap on has a good one here in the states for around $30?

Ok, the rad is flushed and 'probably' not clogged.
There's still all those passages that carry coolant to and from the engine.
This summer I had an overheating problem (it blinked on me too) and it turned out to be a split suicide hose (so instead of coolant flowing to the engine, it slowly exited under the intake). A hint to a blown coolant hose is the smell of coolant to me, but since you just use water, that may not work for you.
A week later, one of the hoses that go from the engine to the heater valve blew on me dumping yet another fill of toyota red.

Of note is I ran a draino crystals solution through the rad And engine.
Well, the 23 year old coolant hoses needed replacing anyway and the draino solution was probably the straw that broke the camels back. But once the hoses were replaced, the temp returned to the 1/2 mark, even in 100 degree weather at 80mph.

Ken

[BillyM]

Wah woah woah guys... easy shit first.

Upand down temperature is usually caused by a sticky thermostat. 3 bolts, $15, 5min
If your radiator cap is older than a couple of years, replace it too.

Do that first, then come back if it keeps it up.

--BillyM

[ma71supraturbo]

While youre replacing that thermostat and radiator cap, check ALL of the radiator hoses. If any are bulging or show any crustation near the clamps replace them. A leak (even a small one) will give BHG-like symptoms as it introduces air into the system...

[AJ]

Make sure you get a Toyota OEM cap and thermostat.

[supramad77]

How long do thermostats last . I can remember replacing mine prolly in the last four years.
The rad cap was on the car when i got it.

Wah woah woah guys... easy shit first.

Upand down temperature is usually caused by a sticky thermostat. 3 bolts, $15, 5min
If your radiator cap is older than a couple of years, replace it too.

Do that first, then come back if it keeps it up.

--BillyM

[BillyM]

....too many variables to say Pat. I've gotten bad aftermarket ones out of the box, and then again, I've had original ones only replaced 20 years later in some of my cars. All I know is that they are cheap, easy to replace, and can cause the exact thing you are referring to.

One thing I forgot to mention, get ahold of a system pressure tester. It will have a pump, gauge, and hose running to a standard radiator cap. Pump it up to about 20psi and let it sit for an hour. If you get drips under your car, and or the pressure goes down, you have leaks that you need to get taken care of. ...but still swap that thermostat and cap with factory parts.

One other thing that can introduce air into your system and make you lose coolant, pop the lid of your overflow tank, make sure the rubber gasket under the lid is in good condition. Once it starts getting thin, it is worth cutting out a piece of rubber and replacing it. If it doesn't seal, the system wont draw antifreeze back in as it cycles hot and cold every time you drive it.

--BillyM

[supramad77]

I removed the thermostat and ran the car for a couple of days with no problems. However i tested the thermostat in boiling water and it is working. It is still quite shiny as it was not all that old.
So it is back in to see what happens.
BTW i have flushed out the rad flush and the water looked like it had oil in there. I am not sure if it was the rad flush making it look oily or it is indeed oil from the engine.

[Moorman]

Wah woah woah guys... easy shit first.


--BillyM

Yes, fan clutch, easy shit.