Alright, so this recently started up
First things first, my fans seem to be running a bit more than usual.

Second, as long as the car is in motion, she'll stay at 210, but once the car sits for a bit (like at a red light), the temp rises. Can get all the way 240-250, but RARELY gets to 260.

Coolant looks fine, and I hadn't noticed any leaks anywhere. Well, coolant is a bit dirty, so I'll definitely be doing a flush on my next day off. Hadn't really had time to do much diagnosis, but I'm just looking for some opinions and suggestions from you guys.

Thanks!

 

I'd try flushing it and see where that gets you, it's pretty inexpensive and can be done fairly easily.

Other than that maybe change the radiator cap. Sometimes they get old and don't hold pressure like they should, causing temp issues. They're also pretty cheap and even if it's not bad it's always nice to do preventative maintenance.

 

A flush ia always good. But coolant can be incredibly dirty, as long as its topped off and flowing, it will cool. It sounds you have a fan issue.

When your moving, as you probably know, the lower air dam does almost all of the cooling. When you slow down and/or stop and the temps quickly rise, the fans come on and they are responsible for 100% of the cooling. Big task.

Make sure BOTH fans come on together. And also, make sure they work in BOTH low and high settings, which should also happen together. If only one fan is coming on, you have a problem. They always work together.

Make sure there's nothing stuck up in front of your condensor like a bag or anything that will reduce airflow over the condensor surface. At speed you will cool enough to keep it from overheating, but when you stop it will heat up fast if there's any blockage up there.

If you do a flush.....take the extra time and do it right. Remove the t-stat and then bolt the housing back on. Remove the radiator cap for this entire process. Start the engine and let the old dirty coolant drain out while you keep the water hose running into the radiator. Flush it until the water runs out clean. No more dirty coolant. Stop the engine. Then close the drain plug and pour a half gallon of Formula 88 degreaser in the radiator. Start it up again. Then keep topping it off with water water until its topped off and circulating through the system. ((By removing the tstat you will have flow the entire time)).
Let it idle for about 5 minutes making sure its topped off the whole time, let the engine warm up that mixture and mix it around.
Let it sit for 4 hours.
Then drain the radiator. Close the drain and fill with water. Start the engine for 10 seconds to move the water around. Drain the radiator again. Then you can leave thee drain open and just let it drain until the water runs fresh out of the drain. Keep the hose in the radiator fill cap to keep it topped off.
Might take a while because degreaser will suds up like soap.

When its all clean.....close the drain. Put the t-stat back in with a new gasket.

Then....replace all the coolant with GREEN coolant. NOT DEXCOOL. You will run cooler with GREEN coolant.
Also, add one bottle of Water Wetter.

And....a brand new radiator cap is a must. One of the most overlooked items that cause overheating, a new cap. For $6.00-$10.00 I replace my cap every year.

NOTE...during this entire process...I highly recommend having a friend just sit in the drivers seat and watch your temp guage the entire time just to make sure you never overheat for some reason. No reason you should overheat...but it would suck to be out in front of the car doing everything and for some strange reason you overheat and don't know it........

.

 

Thanks for the response guys. Especially your lengthy writeup LS6427. Much appreciated. Both fans were kicking in fine, so that's when I did a pressure test; noticed no leaks. I ended up doing a full coolant flush with the green coolant, changed the thermostat and gasket. Now she's running with no overheating issues!

My coolant was quite a bit dirty, and a bit low as well. Presumably due to not changing it in a few years. I guess it'll be doing another flush soon when I swap my heads/cam in the next month or so.

P.S. I did buy a new radiator cap too. Thanks again for the suggestion, didn't even think of that.

 

Well, bringing up the topic again.

So... The issue was resolved for a couple months (mid March, as this thread originally ended), and now the same issue persists. It's not as severe as before, but as long as I'm idling, the temperature will slowly rise, to almost 260; redline. As soon as I start driving, the temp goes back down. Both fans kick on after 210
Highway driving is perfectly fine, and the temp stays at a constant 210, and doesn't move in the slightest.

As long as the car is in motion, even at like 10-15mph, the temp gauge will revert back to 210.

I did a full coolant flush, and replaced the thermostat/gasket a couple months back, as well as replacing the radiator cap; as my last post stated, car has been running perfectly fine until just a couple days ago.

And there are no leaks, coolant looks fine, and I ran a compression test, which also read fine. I'm at a loss here.

Any other thoughts!?

 

Do a pressure test on the cooling system to see if you have an internal leak.

Also, bleed air from the steam crossover tube. If you keep getting air from here over say a week, then there is a leak.

 

I'll ask the obvious: did you make sure the front of the radiator it's clear? Also, is your air dam still attached and not jacked up?

 

Pressure test read fine. No leaks.

Air dam is indeed attached. A few scruff marks on the bottom, but otherwise good. Even so, doesn't the air dam benefit when the car is in motion?
Radiator is clear as well; one of the first things I checked.

A bad coolant temp sensor wouldn't case this issue, would it?

 

How old are the rad hoses? I just replaced mine when I was have the same problem and the drive home was fine and idling for a couple minutes was ok. This was in a 90 degree day.

 

I would start looking at the water pump. If it is damaged internally it could circulate better while driving than at idle. I'd do a new w/p, 160* stat, and tune the fans for the lower temp and enjoy.

 

This was gonna be my next question.

Nest time the temps get up to around 230-240*F....immediately pull over and pop the hood. If you can keep your hand on the intake, or on the TB, or on the strut tower brace.....and not burn it....then you are not running hot at all. Its a bad coolant temp sensor.
If you're really getting up to 240-250*F you cannot keep your hand on the intake for more than 2 seconds.

I had this happen years ago, drove me nuts. I was never getting hot....just a bad sensor.

.