Recently my 99 blazer the the coolant temp goes up to 260 then drops rapidly to about 210. My regular temp that I have noticed is around 200-210. Only does this when I first start driving, then later stays at 200-210. I haven't done anything to allow air in the coolant, but is sounds like air in the coolant but I could be wrong. What do you guys think?

 

Yep, sounds like air to me. Have you flushed the system, changed the thermostat, or opened the system for any reason lately?

 

Nope. Just to add coolant to the reserve tank if need. I was thinking of getting it flushed out tomorrow though. The radiator cap looks newer, I have only had for 2 years, I might pick up another. I just took a drive in it while ago but before I did I added some coolant because it was bare since the last time back in March. I drove it, it did the same thing about 3 times up and down and then one the way back home for 4 miles it stayed steady at 190-200. Any suggestions?

 

If you're having to add coolant, then you're losing coolant due to a leak somewhere and possibly sucking in air. I suggest a coolant system pressure check to try to find the leak and correct it before doing a system flush.

 

No, I am not having a to add fluid constantly. What I meant was, today is the first time I added coolant since March. I did have a problem with the heater core clogging up about 2 years ago when I first had it, but I blew it out, worked fine ever since.

 

Well, after further review, my low coolant light sensor must not be working or they do have one?, Either case, coolant I put in the reserve, it took about a 1/4 of it. That would explain why for 4 miles it stayed at regular temp. I am driving a semi long distance tomorrow and will see if it acts up. My theory on why the coolant is low, probably my heater core and if it is, it is a small leak. I just have to keep a regular check on my coolant.

 

Well to follow up on my problem. I found out later my water pump was going bad which caused a coolant leak. This was an odd but good thing. All the pump did was leak, no visible damage on the old pump and the fan was wabbling like they usually do when one goes out. I had someone replace it for a change. I usually do it myself. Got 2 benefits from doing this. Found a good mechanic and he found a belt tensioner was bad as well.