Stephen Meredith

Hope you all can give me some advice.

Symptoms:
Sits around around 226-238 at idle with ac on (93 degree days lately)
While driving to work. At 70mph approx. 2k rpm, with AC OFF car stayed at 244 & would jump to 248 uphill then right back down to 244 on level road.
If I turn the AC ON it would jump over 250 within seconds.

What I've tried:
"Burping" the system
Replacing thermostat with 160 degree replacement.
Cleaning all the grass clippings & crap from the radiator with an air nozzle & brush.
None of these have changed the outcome.

ArtClassShank

Water pump? Any coolant leaks? Maybe the coolant temperature sensor? Air pockets? Fans coming on?

stevebz06

There are two cooling fan relays, low speed and high speed. If the fan is running only at low speed it could cause this. But if it doesn't cool off when there is airflow at highway speed, something else is wrong and I would look for a collapsing hose, slipping serpentine belt, etc.

neutron82

there are actually 3 fan relays but the fans should not be an issue at cruising speeds... do you still have the lower air dam installed?... you do need it but I'm not sure if it being missing could cause that big of an increase in temps while cruising

Stephen Meredith

The factory lower air dam is intact.
The hi speed fans works as it should (coming on around 230), but the EBCM is behind the low speed fan, so I can't see it to tell if it's working correctly.
No coolant leaks that I see. I would think the water pump is working because both radiator hoses get hot & i've got strong heat blowing out the vents when I turn them on.

It's hard to diagnose it at idle & sitting still because it won't jump to 240+ unless i'm driving & under load (at least 1800 rpm or so). If I'm going down the road doing 35 there's no problem.

Now I did notice when I got back into town tonight, getting underneath it, the ac condenser is bowed out just a little. Like maybe the previous owner started to jack it up on that flimsy bar directly underneath it then stopped as soon as it started bending. But there's no damage to the ac condenser, just a slight curve to it & the ac has never lost any refrigerant.

tommypenguin

Is your Coolant reservoir full?

Stephen Meredith

Good info for me to check after work tomorrow. I know the cap doesn't leak, but don't know if it's holding proper pressure.

I DO know that passenger side fan DID NOT come on at all until near the 230 degree range when I watched it today.

tiojames

Had the same problem with my C5. Took it to Cordes Racing in Phoenix-problem was the fuse or what ever it's called. S20 dollars later I was on my way.

3sACROWD

If you turn your heat on high, does your engine temp go down? If yes, that is a good indicator that your radiator is plugged. It is either still plugged up externally or could be crudded up on the inside.

My radiator was gunked up on the inside and once replaced, all was good. I had well over 200k miles when I changed it. Hope that helps

Stephen Meredith

Ok. Problem NOT fixed. It only starts overheating at highway speeds (65mph/approx 1,600rpm & above). The temps drops right down in town at low speeds & stoplights.

Here's what I've tried as of today.

• pulled radiator - pressure washed/foam cleaned/pressure washed again/brushed
• foam cleaned & pressure washed SC condenser
• flushed coolant system
• changed out thermostat again
• checked air dam to make sure it's not bent
• tested fans to make sure they are working properly
• thoroughly checked oil for any sign of coolant
• refilled with new coolant
• bled air with the steam vent tubes on the heads method

Hit the interstate with the ac on & in 2 miles at 85mph (approx 2500rpm) the temp was up to 237 degrees. Let it cool down to 226 & ran the same 2 mile stretch at the same speed with the AC off & it got up to 234 degrees. It cooled down to 220 at stoplights on the way home & I ran the last stretch of road (4 miles) at 65mph with the ac on and it slowly crept up to 234 again. Turning the heat on didn't make the temp go down

I am completely out of ideas aside from throwing money at it (new radiator/water pump), But th

neutron82

you don't happen to have an iron block in the car do you?

Stephen Meredith

I installed a new reservoir tank & cap today. And water seemed to flow freely through the radiator when I had it out. put the hose in one side & it gushed out the other.

I don't seem to be physically losing any coolant as their isn't any on the ground & the tank stays at the same level. But what is the best way to check for a leaking head gasket beside checking the oil for coolant? And I guess there isn't a way to test the water pump other than replacing it?

Stephen Meredith

I hate to throw money that I can't really afford right now at this guessing, but this car is normally my DD & I'm forced to drive my escalade until it's fixed. And 400+ miles a week just to work & back has my dumping well over $100 in gas into it.

So I ordered a new ac delco water pump today. Hopefully that fixes it, but if not, a dual core radiator will be next. And pulling the heads will be my last resort.

Hopefully when I solve this eventually, it might help someone else in the future.

JPW501

That would be my bet. Good luck.

Stephen Meredith

Thanks! I went back through the amazon reviews for this ac delco part number & it appears its the new style pump with the pressed back cover instead of bolts. But according to a few customers it can fit either thermostat style & comes with a gasket for the new style & o-ring for the old style. Part number is 252-846. I'll find out for sure when it get's here & if it does have to have the new style thermostat, I'll pull the one off my LS swapped Nissan in storage.

Either way, this one was ridiculously cheaper than the $139 for 01 pump at autozone & $200+ for 04 model pump!

Stephen Meredith

Ok, I see what you are saying. Thermostat seal on new vs o-ring for the old style on the housing itself. Looking at the picture of the new water pump. I wonder why it has the gasket on the bottom right? Do I not need to use it?

Stephen Meredith

Got the new water pump on. It seems to have solved the problem. This new water pump DOES work with both the old style & new style thermostats. It even came with instructions for using either one. So this water pump is a great solution for anyone wanting a genuine acdelco.

vipmiller803

That's excellent news! Any chance you can tear up the old one to see how the impeller looks? I'm curious to see a water pump be poor enough to cause this sort of behavior.

DWC4

Radiator Cap! 2003 C5, 100k miles - Well I suddenly had similar overheating problems a couple weeks ago and discovered I was about a gallon low on coolant. Topped it off, better but still some overheating a bit, hitting 235F which it never did unless in stop and go on a hot day with AC etc.

I considered all the costly and complicated suggestions and fixes above (thanks all!) and then suddenly, when checking my coolant level again the other day noticed - duh- there was a white trail from under the cap down the side of the reservoir tank. And then I looked more closely at what I had thought on a previous 'quick look' was a perfectly good radiator cap, but it was not - its' plastic was cracked, clearly a bit warped, etc.

$10 on Amazon a new AC DELCO OEM replacement is on the way. I was not keeping a pressurized system and thus the temp was creeping up.

Start simple is my new mantra.