Temp goes from 140-260 and back Heat no heat???

[unsane]

My temp is going from nearly 140 to 260 in a matter of seconds. It keeps doing this back and forth. It takes the heat away then the heat comes back on. Is this a thermostat? I am not real good at cooling system problems. Also it has ben below zero thelast couple of days, this is when all of this started. Thanks in advance for your help

 

[Sparky87k5]

Sounds like you're low on water in the radiator or possibly your radiator is trying to freeze up. Check water level and anti-freeze condition. In cold climates, should be at least -30F and I always ran -40F to be safe.

 

[Grim-Reaper]

Vortec heads?

GM had a problem in the 90's that I'm not sure of when it started but it's on surpentine belt engines. The coolant created a air pocket in the head where the sensor is. It would cause those exact symptoms. My 95 company Vandura had the problem and when I ran it to the dealer for it they had three other trucks sitting there with the same problem.
GM is aware of the problem and their fix is actually a waterpump that changes the flow rate. TRW seems to ring a bell as the brand they used.
No heat might be that you have the heater hoses hooked up wrong. The hose to the heater comes off the intake and goes to the bottom connection on the heater. it's a 5/8's hose.
The top connection goes either to the radiator or to the top of the water pump depending on how your truck is equipped.
There have been several people that went top of water pump and radiator instead of top of intake and installing a plug in the water pump and dumping to the radiator.
195deg thermostat is what GM has spected for all FI engines and even the carb engines GM recomends a 195.

 

[BigJohnson]

I have a 96 Vortec 350 and have strange cooling problems every now and then. I am running a v-belt setup. Is the TRW pump for a surpuntine setup? I guess I might should get a better flowing v-belt pump. Where can I find more info on this problem?

Thanks
Jordan

 

[Grim-Reaper]

My undersatindin the pump was moving the coolant to fast and it was cavitating. Weird thing is ir was fine for 10k then with no warning it did that. They swapped pumps and to this day it has been fine. It was a 95 and to be quite hones with it being a company van I never did more than check oil on it. When it had a problem I dumped it at the dealer and let them bill the company. I think it was a vortec motor but I might be wrong. it was a 5.7.

 

[dyeager535]

Just for general knowledge, 5.7 Vortecs didn't start until 1996.

I've *heard* GM called some of the earlier 4.3L motors "Vortec" but not sure if they had the actual good head design, if that was just marketing at the time, or if someone just didn't know what the heck they were talking about when they said they were called Vortec's.

 

[BigJohnson]

Well, if it’s too fast I should be ok with my el cheapo water pump /forums/images/graemlins/wink.gif I do have what I would think are pretty drastic changes in temp. Jumping 20-25 degrees very quickly in any direction makes me think my gauge is not reading properly. I don't know how fast a change can take place.

As far as 140-160...my water pump went out and I replaced it with a rebuilt unit. I had the same thing, cool to very hot and quick. After replacing the thermostat that wasn't bad and trying other things I replaced the pump. The rebuilt unit I bought was defective and didn't flow properly. It’s sad really because the new pump was only a few dollars more.... definitely worth the time and trouble it caused me troubleshooting and replacing the bad new one.


Jordan

 

[dyeager535]

Does the gauge "warm up" properly? Basically, go from cold in the morning, up to whatever temp it starts bouncing around?

 

[Brian 89KBlazer]

Just finished a few months of this with my Lumina. Exact same symptoms. I'll bet (if I was a bettin man /forums/images/graemlins/wink.gif) that as one person mentioned before, it's an air pocket in the cooling system along with low coolant. Purge the air, fill the system & the heat will return. If it works for a while & then starts again; pick up a pack of stop leak & throw in when you purge & refill again cause you got a small leak in the system that's letting fluid out & air in. Worked like a charm for me! /forums/images/graemlins/smile.gif

Good Luck

 

[smack]

Grim, "The hose to the heater comes off the intake and goes to the bottom connection on the heater. it's a 5/8's hose.
The top connection goes either to the radiator or to the top of the water pump depending on how your truck is equipped."

Are you sure about that?? Mine's the opposite and I have okay heat and before I make a mess to flip it I wanna make sure.
smack
p.s. I still haven't figured out how to quote properly.