Crazy engine temp fluctuations. New wataer pump and thermostat.

[XHitman396]

Well first off, hello for the first time in like 3 years. College is very busy and expensive, and leaves little time for tinkering. And thank God nothing has come up I couldn't easily handle. On to the problem:

I've got an '87 K5 350, pretty much stock. I swapped the water pump probably a month or so ago because it was leaking, and had no issues regarding over-heating or anything. After the swap, I noticed the temp would warm up initially a bit more than usual before the thermostat would open up and the temp would settle to around 200. So, natually, I changed the thermostat as I've had to do before for the same issue. Seemed to work for a while, now it's going hay-wire.

The temp gauge is reading all over the place. Especially for the initial warm-up. Today I had to pull off a main road into a neighborhood because the temp reached redline. Then it cooled a bit, and never got to a dangerous point after that. But it fluctuates readily between about 180 and 230.

It sounds to me like I just got a bad thermostat, but it made me wonder since I had zero problems until I swapped that pump. The radiator was flushed not too long ago, and the coolant's new. Anyone heard of this or offer another explanation?? Thanks in advance for the help.

 

[XHitman396]

Aww hell... I meant to spell it 'water' in the title, before I get called out for it...

 

[down4thakrown]

make sure you put the thermostat in the rite way and that the wire goin to the sending unit on the heat sensor is in good condition...

 

[blazinzuk]

What type of thermostat, Stant?

Those things suck might want to try to change it out.

Other thing could be the gauge

 

[4X4HIGH]

Couple of things, if the overheat issue started AFTER you installed the new pump then either you have the wrong pump (serp style is reverse rotation) make sure you don't have a serp pump or you have air trapped in the system still. Thermostats do fail but hardly ever do you buy a bad one out of the box. Now if you happened to have installed or a PO installed a serp system then it requires a reverse rotation pump and if you installed a factory pump for an 87 K5 it is standard rotation and will overheat all day. My best guess though from your explanation is that you still have an air pocket trapped somewhere.

 

[XHitman396]

I do not know what kind of thermostat it is. $7 one from O'Reilly's. I thought it seemed odd that a new one came bad considering their easy of construction, but I don't know what else it would be.

No on having a serp system on it. I suppose it could be a serp pump, but is there a part number on it or anything I could see it? How would one go about getting an air pocket out of a cooling system?

Replacing the thermostat seems easiest, unless you know a remedy for this air pocket business. I'll dabble with it tomorrow, I suppose. Thanks.

 

[blazinzuk]

Never really had a problem with air bubbles but I believe all you do is take the cap off and let it run for a while. Of course watching the temp guage but the thermostat has to be open

 

[Cornfield creations]

I would try an AC delco thermostat, and drill a tiny hole in it, like 1/8, just in case of air trapped beneath it. Then I would look at the water pump for the reverse rotation like 4x4HIGH mentioned. You can get a water pump where someone installed the propeller wrong. So even if it turns out to be the correct water pump then keep that in mind also.

 

[ryoken]

Well first off, hello for the first time in like 3 years. College is very busy and expensive, and leaves little time for tinkering. And thank God nothing has come up I couldn't easily handle. On to the problem:

I've got an '87 K5 350, pretty much stock. I swapped the water pump probably a month or so ago because it was leaking, and had no issues regarding over-heating or anything. After the swap, I noticed the temp would warm up initially a bit more than usual before the thermostat would open up and the temp would settle to around 200. So, natually, I changed the thermostat as I've had to do before for the same issue. Seemed to work for a while, now it's going hay-wire.

The temp gauge is reading all over the place. Especially for the initial warm-up. Today I had to pull off a main road into a neighborhood because the temp reached redline. Then it cooled a bit, and never got to a dangerous point after that. But it fluctuates readily between about 180 and 230.

It sounds to me like I just got a bad thermostat, but it made me wonder since I had zero problems until I swapped that pump. The radiator was flushed not too long ago, and the coolant's new. Anyone heard of this or offer another explanation?? Thanks in advance for the help.

is the truck actually overheating?

I would verify the temps with an IR gun.... EVERYONE should own one of these.. they're only about $50....

 

[rocknerd]

is the truck actually overheating?

I would verify the temps with an IR gun.... EVERYONE should own one of these.. they're only about $50....

x2... mine just reads high.. don't know why but after a thermostat, guage, etc.. checked the engine temp and guage just reads high. engine runs at good temp.