Temperature question K1500

My 97' 5.0L 1500 temperature guage is acting a bit odd. It gets up to about the 190 range then drops down to about 150-160. After about 2 mins, it repeats to 190 and drops, and so on and so on. Is this a thermostat issue or something else?

Did you recently have any cooling system work done? Is the coolant reservoir up to the "cold" mark when cold and the "hot" mark when hot?

Did you recently have any cooling system work done? Is the coolant reservoir up to the "cold" mark when cold and the "hot" mark when hot?

No work done. Seems to be at normal levels.

change the thermostate

I second that. replacing the thermostat would be one of the first things I would replace in this situation.
You covered the fluid level.

Ok, change of news. Its losing coolant badly now. So based off that, I looked in the oil. Oil looks pretty good, but the cap and filler valve had the crusty yellow stuff on it. Not much is getting in there. I think it is probably the intake manifold gasket, but could it be the head gasket? Anything else? I would think based off the amount of fluid it is losing, it would not be the head gasket. Any help would be great.

How much coolant is badly?
crusty to me is a hard type substance. that would indicate to me it has been there a while.
Now a light brownish tan goop type substance indicates fresh build up.
Was the cap clean when you did the last oil change and how long ago was that?
Have you done a pressure leek down test?
A general pressure test?
How does the exhaust look?
white smoke/steam indicates moisture.
can you smell the sweet smell of antifreeze in the exhaust fumes? all indications of a head gasket.
an internal leek can bee frustrating.
If you dig into it and pull the intake you should be able to see where the leak was. Hopefully.
If you dont find indication of a gasket blown, chances are the head gasket is bad. I had a friend who did a radiator/block flush and found his leak right away.
Oh yea, you said the oil " didnt look bad " explain that better.

change the thermostate

I wanted to follow up on this. I recently changed the thermostat in my '97. Autozone said they had a good price on a fail-safe that would stay open if it failed. I bought it and now and having the exact same condition you described about hitting 190, dropping to 150 back up and so on. My step dad mentioned that next time, I shouldn't get a fail-safe stat and that might be what's causing the fluctuation. He also said he's never had a stat fail in the closed position.

I'd be interested to hear the thoughts of others.

Mine was in autozone too. Think its time to change that out.

I wanted to follow up on this. I recently changed the thermostat in my '97. Autozone said they had a good price on a fail-safe that would stay open if it failed. I bought it and now and having the exact same condition you described about hitting 190, dropping to 150 back up and so on. My step dad mentioned that next time, I shouldn't get a fail-safe stat and that might be what's causing the fluctuation. He also said he's never had a stat fail in the closed position.

I'd be interested to hear the thoughts of others.
thermostats should be replaced when coolant is replaced. thermostats are cheap and hopefully last until next coolant servicing. a thermostat will fail in any possible way including not opening at all. if temperature is not regulating it is most likely the thermostat. this is assuming that coolant is not leaking if you add coolant you have leak if you have leak pressure will drop then the coolant will boil then water pump cannot pump air bubbles then its all over .......