View Full Version : Strange coolant/heat issue 99 STS

07-17-09, 04:05 PM
'99 STS 120k Miles, driven hard of course :>

I posted about this before a while ago.. but it's still giving me issues.
Before I wasn't loosing any coolant but now I'm losing a lot of it and I can't figure out where it's going, which is bad. At Idle the temp gauge goes up pretty high and then goes back down, if i'm driving on highway it stays normal. If i rev up the engine at idle it goes back down. Someone said my radiator was clogged which may be the case but I have no way to determine this. I can smell coolant under the hood but I've looked everywhere and can't find where it's coming from. It's not in the oil, or in the tranny fluid and not coming out the exhaust, and I had a test for exhaust gases in the coolant and didn't find any.
I was just driving it and dealing with the strange temperature swings, but now that it's losing coolant I need to do something about it.

IF anyone has any ideas before I replace the radiator, let me know please! Thanks!

07-17-09, 05:11 PM
Radiator side tanks. The front is blocked by the condenser and the seeping coolant may be evaporating before it drips.

07-18-09, 11:24 AM
At 120,000 miles you may have a fatigued spot or small crack in one of the radiator side tanks. As your car heats up and pressure builds this crack opens up allowing coolant to spray out. Check your radiator and your hoses and hose connections. I would bet on the radiator.

07-18-09, 07:01 PM
Take the radiator out, flush it with a water hose. Check the end tanks for cracks or leaks.

Bill Wagensveld
07-18-09, 08:06 PM
You might want to make this simple check before you do anything drastic. A VERY common problem with Northstars is a clogged coolant return line, disconnect from top of engine and blow through it. Also, with that car running and the line disconnected there should be a strong flow. If cloged clear out with a wire. Another regular probem is TRAPPED AIR, if the top and bottom rad hoses are warm but the rad is cold, this is it, you can lose a gallon with no visable leakang because it drops out the overflow while you are driving.

Anyway, like I said, you could check these things before doing anything expensive.

Mr. Bill

07-20-09, 04:49 PM
Which is the coolant return line? The little teeny hose on top near the overflow? I think it might be the radiator, there's tons of trapped air in there when i open the coolant cap it comes blasting out and i have to put in quite a lot of coolant.. It wasn't losing coolant before but it was doing the overheat thing and having high air pressure in there when i opened the cap, and after driving it that way for a while it now is losing coolant so I assume the high pressure probably opened a hole somewhere that i can't find. I looked everywhere i could with a flashlight but i can't find where it's coming from.
I know something is clogged somewhere, just can't find the darn thing. I guess I'll have to take apart the radiator and all the hoses and see what's going on with it. Any suggestions as where to begin, or simply the radiator and return hose? Thanks for all your replies!

07-20-09, 06:29 PM
There is no coolant return line. The small (3/8" ?) line from the nipple at the top of the surge tank to the nipple at the water pump bypass area is known as a "purge line". Its function is to constantly bleed a small portion of the coolant from near the high side of the system to the airspace above the coolant in the surge tank in order to clear the block of air bubbles, thereby preventing water pump cavitation and hot spots caused by trapped air/gasses (sort of like a reverse blood clot).

The surge tank rides on the sealed system (the 1" hose connector at the bottom) and accepts the expansion and contraction of the coolant caused by heating and cooling. There should be a considerable air volume over the coolant to allow for this change, so the proper level of coolant is halfway up in the tank, COLD. With the engine cold and the cap on the tank you will lose little coolant if you disconnect first one end of the purge line, then the other, and make sure the nipples are clear - use either weedwhacker monofilament or a small drill bit, twisted carefully, to check for obstructions. Place a plastic bag down over the EBCM in order to prevent coolant from touching any part of the block or harness.

07-21-09, 06:51 PM
Finally found a leak coming from somewhere on the passenger side on the radiator somewhere, i can see it dripping but still can't see the spot where it's coming out at.. I guess that's issue #1, the issue #2 is how did the radiator get clogged in the first place which probably caused excessive pressure which resulted in this leak forming.. The bypass tube and all that looks fine I checked it. I think the mechanic I talked to months ago was right about a clogged radiator. Am I correct that the coolant flows from the passenger side to the drivers side?


07-21-09, 10:22 PM
The leak is likely the plastic side tank. Heat/cool cycles take their toll. IF your radiator is truly clogged, it is likely from too much cooling system supplement (sealant tabs) or calcium, lime, iron etc from tap water.

07-22-09, 05:30 PM
Yeah something's definitely clogged up.. taking it apart to find out.. will post back.. WHy would they make a plastic side tank? heh..why not aluminum.. ah well.. at least it's not a head gasket :P

07-22-09, 05:35 PM
Oh and I guess not many people post things like this in a thread when they ask a question about something breaking.. But, the car is 11 years old, has 120k miles and this is the only problem i've ever had with something actually breaking on it.. Besides the regular..brakes,plugs,wires,shocks,isc motor, and i did engine mounts although i didn't have to.. so Just wanted to say that 11 years and no major problem and the worst it can do is a clogged radiator? I'd have to say that's pretty good run :>

07-22-09, 06:18 PM
Yes, coolant flows from the engine block through the upper hose to the top passenger side and through the radiator core to the center of the driver's side tank, thence to the water pump/bypass fitting.

When/if you install the new radiator make sure the upper hose is either clipped into the channel in the plastic sight shield rear lower edge OR wire-tied to the support bracket - a loose hose will chafe on the cam cover and maybe something else.......