mbd77

Hey- I need some help. 2003 with 25,000 miles.

Here's the situation:
running hot at idle, jumps up to 229 and hotter some times, fans kick on, cools back down, heats up again.
In 6th gear at 1500 RPM's the temp stays at about 205-208 (sometimes hotter)
In 5th gear at 2000 RPM's the temp drops to 201-205
in fourth gear at higher RPM's the temp drops even lower, to around 198, but never gets below 198.

But then at idle, it stays hot and won't cool down......fans just keep cycling when temp reaches top and bottom of fan range.

I replaced the thermostat and coolant.

The fans do work, I've replaced all 3 relays just to be sure.

No blockage on the radiator in front or behind.

The outside temp was 37 on my drive tonight, I thought it would run a little cooler than normal, but the cool outside air doesn't seem to make it run any cooler.
My next move is to replace the water pump..

Any thoughts- please help.
Thanks

Quicksilver Vert 01

It sounds like there's still some trapped air in the cooling system.
I wouldn't suspect the water pump yet, at only 25K miles.

Try driving it, with the surge tank cap not fully tightened, for a half hour or so. This will help to expel any remaining trapped air.

mbd77

Hey- thanks for the tip. I tried this and it did not work, it just heated up and boiled out!...........
I seem to have some other problem but not sure what to do next....
Thanks for the advice

The NNIAL8R

Those temps arent abnormal........You have a 195 degree thermostat...dont expect the car to run any cooler than it takes to open the t-stat...

GrayC5

All sound pretty normal to me too. This is a topic that come up here very often. Do a Forum search in C5 General and/or C5 Tech on coolant temps, coolant temperature or similar and you should find numerous threads on this topic that should help ease your mind.

dgrant3830

Sounds fairly normal but let me ask... when you said there was no blockage in the front of the condensor...did you check for thousands of small rocks? These cars are like vacuums driving down the road. I found that about once per year, its necessary to either blow out or wash out from the inside to the outside with either an air wand or water wand, all the rocks. I makes a serious difference.

The NNIAL8R

What we often forget is the C5 doesnt have a mechanical fan attatched to the water pump that turns all the time like many older cars have...The mechanical fan of days past kept engines a bit cooler, as the only cooling action our cars get (especially at at idle) is when the electric fans kick on...These electric fans doint even kick on until temps are usually above 220-230...Of course when youre driving down the road the air forced thru the radiator by the simple act of vehicle motion cools the engine substantially...so dont be alarmed when you see temps creep up towards the 230 mark if your sitting in traffic or idling...Besides, the emission systems on these cars require higher operating temps for cleaner emissions

ljthe2nd

You can not operate your car with the coolant cap loose. The cooling system in any car is designed to run under pressure. If you remember any of your high school science (or if you have ever used a pressure cooker) you will remember that the boiling point of water rises as pressure rises, that is the point of keeping the cooling system under pressure (the coolant can be above 212 degrees F and not boil) Your car is designed to run above 212 F at an idle and if you don't have the cap tight there will be no pressure so the coolant will boil and because the cap isn't tight it will just boil out. Do not ever operate you car without the coolant cap tight.

CircledWagons

What is the optimum temperature for the tstat to open?

GrayC5

Quite true.

Following is a condensed description of how the cooling fans work for model years 2001 through 2004. (For earlier model years 1997 through 2000, the stock fan temp set points are somewhat different.) This information along with a full description of how the cooling system works can be found in the Engine Section under Cooling System Description and Operation of the GM Service Manual specific to each model year:

Cooling Fan Operation:

For model years 2001 through 2004, the PCM operates (commands) the 2 fans together as follows:

The engine cooling fan system consists of two electrical cooling fans and 3 fan relays. The relays are arranged in a series/parallel configuration that allows the Powertrain Control Module (PCM) to operate both fans together at low or high speeds.

The low speed is commanded on when the coolant temperature reaches 226 degrees F. It is turned off when the coolant temperature lowers to 219 degrees F. The High speed is commanded on when the coolant temperature reaches 235 degrees F. It is turned off if the coolant temperature lowers to 226 degrees F. When the A/C is on and the coolant temperature reaches 185 degrees F, the low speed will be turned on when vehicle speeds are less than 35 mph.

The NNIAL8R

Most stock t-stats open at 195 degrees......Colder t-stats (160 degree) are available for C5s, and do have some positive "performance" benefits....but Im not sold on the idea....For one, "if" you drive your Vette in cold weather the heater will not be warm enough...but my main concern would be for the possible ill affects the colder operating temp would have on combustion chamber deposits, emission systems, and other temperature related issues....

mbd77

ALL: great information.

When you see your temp. jump to 220-230 you worry. From reading NUMEROUS threads, it sounds like i can quit eyeballing the temp. guage as I drive, this sounds to be normal temps.
I may try a slightly cooler thermostat, have the fans programmed to kick in earlier, and try Water Wetter. But, it sounds like any changes in this temp. range may have ill effects on the engine performance...........

Any thoughts on the Water Wetter?

widewheel

Are you loosing any coolant? I had a similar experience about a year ago except there occasionally seemed to be a small amount of coolant leaking out somewhere. I finally caught a couple of drops of coolant under the water pump pulley after a long drive. The engine would run what I thought was hot (203-210) on the road. In traffic in town it would heat up to 225+ (which is normal). After discovering the waterpump shaft leak I replaced the pump. It is one of the easiest pumps I have ever replaced. I bought a NAPA pump and 185 thermostat. I also replaced the surge tank cap as it appeared to have a crack inside the lid. It has been in the 40's here in Oklahoma for the last couple of weeks and the car will run in the high 180's to low 190's on the highway. Last summer in 100+ temps it never got above 205 on the highway and usually the temp gauge was glued at 198. Air in the cooling system can cause higher temps. There is an elaborate purging procedure in my shop manuals which involves filling the system then ideling the engine to 210 then removing the cap and topping off the system. This is repeated several times till the surge tank will not accept any more coolant. I would not drive around with the surge tank cap off though.