Thread: n00b and a cooling problem

Hello, from Florida.

I am the proud new owner of a 1998 Grand Prix GT, with the 3800 Series 2. Has around 196k miles on it. Runs great, just needs a motor mount.

It's also having a weird cooling problem. The radiator fans come on immediately after starting the engine, and they stay on until I turn the engine off. However, the temp gauge on the dash will warm up (it takes a while to do this) and hover around the 210 mark for a few minutes, then it will slowly creep up around 240 or so. Every now and then, it may reach 250 or so when stopped in traffic. The temp light hasn't come on yet.

According to the previous owner, he's installed a new water pump, new thermostat, and new intake manifold (is the intake manifold underneath the fuel rail? If so, it has a lot of corrosion on the top of it). The cooling system has not been flushed recently. The top radiator hose feels hot to the touch, but I haven't thought to feel the bottom hose to see if the water is circulating in the radiator correctly. I noticed that the small hose going from the radiator fill neck to the coolant reservoir was over the driver's side rail, and was being restricted when the hood was closed, so I re-routed it under the rail.

I've done a quick search in this forum, and someone with a similar problem mentioned it may be a coolant temperature sensor. Personally, I feel that a radiator flush may be in order, since the filler cap is a bit dirty on the bottom, and the coolant itself looks dirty.

Any thoughts, etc, would be greatly appreciated.

Hmm...

Upon further research, I disconnected the coolant temperature sensor's wire harness and took it out. On this harness, there is a black wire, a yellow wire, and a green wire. The harness itself was worn out; the protective tubing had mostly worn off, and what was left crumbled as I touched it. The green wire had a spot where the green sheath had worn off, exposing bare wire. This was probably rubbing against the top of the engine, under the plastic cover. I put some electrical tape around it as a temporary fix (it'll probably melt if left on long enough), and plugged it back in.

When I started the engine, both fans came on, then went off after a couple seconds. I sat there and let the engine warm up. The temp gauge crept up--slowly--between the 100 mark and the 210 mark---around 160 maybe? I felt the upper radiator hose, and it was almost too hot to touch. The lower radiator hose was slightly cooler, but still very warm. So the radiator may be all right.

I drove the car to the end of the road (maybe 3 or 4 miles) and came back. The temp gauge didn't move much, probably because the sun had gone down, and it was cool outside. I got back home, popped the hood, and let the car idle for a few minutes. The radiator fans--both of them--suddenly turned on. I looked at the temp gauge, and it was just above the 210 mark. I revved the engine to maybe 1500 rpm and held it there, and the temp gauge almost immediately went back down to just below 210. A few seconds after that, both fans turned off. I let the car idle, the temp went back up, and the fans turned back on. Even with both fans on, the temp was getting to maybe 235 or so--around the 3/4 mark. Both radiator hoses were hot to the touch. I revved the engine, and the temp went back down to just above 210. I then turned the engine off.

So, the CTS harness probably needs to be replaced. The engine runs hot when idle, but quickly cools back to close to normal temperature when revved up. Both radiator hoses are hot when the engine is warmed up. Both fans come on when the coolant reaches a certain temperature (shouldn't one fan come on, then the other if the temp gets hotter?). The temp gauge appears to be more or less accurate.

Ideas?

EDIT: Another question: Where can I get the CTS wire harness; what part number?

You can just go to a junkyard and cut a good connector off a car there and solder it in place of your bad one.

I don't know what would cause your issues but bleeding the coolant system like mentioned above couldn't hurt. Along with replacing the radiator cap and possibly flushing the system. All relatively cheap and probly need to be done anyway.

IM thinking your radiatior is not working as effiecient as it should be. Have you checked for bugs and leaves stuck to the front of the radiator or the condensor? When the car is warmed up, and the fans are on, is the air infront of the fans nice and hot?

Ok. Bleeding the coolant system of air--I do that by turning the valve on the thermostat housing with the engine running, right? Until coolant starts coming out? The previous owner did replace all those components, so he may not have bled the system. I'll try that soon.

As to flushing the system: I probably should clarify that the top radiator hose warmed up first, then while that hose was warming up, the bottom host warned up too--so there was a small window where the bottom hose was much cooler than the top hose. Should I get the flushing done by the dealer, by a mechanic, or just try doing it myself with distilled water?

The front of the condenser is clean. I have not looked between the condenser and the radiator. I'll try to take a look today after getting home from work. The air the fans are blowing towards the engine is very warm.

Ok, went by Autozone to pick up a brand new CTS connection...turns out it's just a pigtail with one end missing. They actually expect people to just cut the old plug off and splice it on the new wires! I politely refused to pay $17 for a broken connection, and promptly paid ~$30 for a new Haynes manual for the GP. Lame. Looks like I'll be going by pick N pull again...

I got home, and drove the GP down the road and back, then turned the bleed screw a little. It softly hissed for maybe a second, then coolant started coming out. Tightened the screw back up, and drove it up and down the road again. The temperature held at around 180 or so. The sun had gone down (the days seem to be getting shorter for some reason), and it was maybe 68 degrees outside. So it may already be too late for seeing if the temp will hold on a hot day. I got back home and let the car idle, and the temp went up to just above 210 and stayed there. I revved the engine, and the temp went down a little...then I idled it and the temp went up to maybe 230...then cooled back down to just above 210.

Maybe I'm reading too much into a 14-year old temperature gauge?

derp: Thats how all pigtails are sold in the aftermarket.

Not only that but if the pigtail is soldered into the harness correctly it will be a lot stronger than some of the stock connections. I've done my fair share of wire tucks and I find a lot of crimps and electrical tape from the factory.

So I say pick up a new pig tail, a soldering iron, solder, some marine heat shrink, and some wire loom, by the time it's all done you won't even notice a repair was made.