Hello,

My 98 Monte with the 3.1 started to overheat. My only aid while driving was to turn on the AC so the fans would come on until I got the parts. I put a new thermostat and sending unit in, topped off the coolant and bled off as best as I could. I also put in a new fan relay for good measure. My issue now is that I'm still overheating and can't get the fans to come on at all. The upper hose is hot, so I'm guessing that the new thermostat is opening. I made sure it was easy to open before I installed it, but I guess it could be bad once it gets hot.

Any help would be great.

Thanks.

 

Are you sure you're actually over heating? The 3.1's like to climb up the temperature gauge some before the fans kick in.

 

- Are you loosing coolant?
- Is it blowing hot when you have the heater full blast? I know that cna be hard to tell with summer....
- If you can, try having a scan tool hooked up to the car and read the temp the PCM is receiving and see if it matches to what the dash board is reading.

FYI - if there are any air pockets, they read hotter on the temp sensor then coolant.

Just some food for thought.

 

Let me say that I've only had this car for a few months. It sat for a few months while getting fixed. When I first got it, I remember thinking that it always ran cool. The needle was only about a quarter up in the gauge not matter what kind of driving I was doing. The old thermostat had some galling so I'm thinking that it may have been stuck open and when I saw the temps rising, perhaps it closed and stated sticking in either position. You say the temp climbs a bit before the fans kick in? I watched today and the needle just about touched the white mark just before 260* before they came on. While driving the needle rides straight up with a bit of movement to the right, but not much before it comes back down. BTW, The thermostat said 195* on the box. The air is also hot if I turn on the blower I'm pretty sure I have some air in the system still, but I'm not really up on the best way to bleed the system. After the work, I filled the radiator and cracked the bleeder on top of the tube that exits the top of the water pump. I seem to get water only and right away. I had to drive to work this morning, so I went to fill with more coolant before heading home. I opened the radiator cap and didn't see coolant. Before I filled I thought it would be better to open the bleeder but that was incorrect I'm guessing. When I did so, the radiator was/became full... I look in the forum for the proper way to bleed the system, but I can't seem to find it.

 

Well it shouldn't be hitting 260. Mine will creep up to I believe a bit above half way in traffic before the fans kick in. The way I did my cooling system was, fill up the reserve bottle, not the radiator if you need to add more coolant, it'll suck it up. And then with the engine running and it up to temp, open the bleeder screw that's near the thermostat until you get steady coolant. Then I drove it around a bit and repeated those steps a few times to be sure all air was out.

 

It may be helpful to find someone with a scantool that can read the actual sensor reading the PCM is using. It's possible there is a problem with your instrument cluster and the gauge might be incorrect. I don't recall when you fans are supposed to kick on, but that gauge reading sounds high and the fact the fans ARE kicking on says the fans work. I keep going back to wondering what the PCM says.

Here is the fill process from the shop book (please not, this also assumes the drain **** was opened on the radiator and drain plugs removed from the engine block):
- Open the air bleed vent on the thermostat housing.
- Slowly fill the cooling system through the radiator neck using the following procedure:
o If the coolant system has been flushed, first add 100 percent ethylene glycol in the amount listed for the appropriate engine application.
o Slowly add clean water to the system until the level of the coolant mixture has reached the base of the radiator neck.
o Wait for two minutes and recheck the level of the coolant mixture. Add clean water if necessary to restore the coolant mixture level to the base of the radiator neck.

- Install the radiator cap making certain the arrows line up with the overflow tube.
- Close all the air bleeds. DO NOT over-torque the air bleed valve. The air bleed valve is made out of brass.
- Add 0.75 liters (0.80) quarts) of a 50/50 mixture of ethylene glycol and clean water to the coolant recovery reservoir.

Notice: The Low Coolant warning/indicator lamp may come on after this procedure. If after operating the vehicle so that the engine heats up and cools down three times, the Low Coolant warning/indicator lamp does not go out, or fails to come on at the ignition check, and the coolant is above the full cold mark in the reservoir, refer to Low Coolant Warning/Indicator Lamp in Electrical Diagnosis. If at any time the Temperature warning/indicator lamp comes on, immediate action is required. Turn OFF the engine and allow the vehicle to cool. Do not remove the coolant recovery reservoir cap at this time.
Inspect the freeze protection of the engine coolant after the engine heats up and cools down three times using a refractometer or a thermohydrometer to ensure proper freeze -37°C (-34°F) protection. Obtain the coolant mixture for the inspection from the base of the radiator neck, NOT from the coolant recovery reservoir.

 

Thanks for the info guys. When I open the bleeder on the thermostat housing, I'll get a steady stream of water... hot or cold. I'm going to drain and refill just to start off correctly and because the coolant that is in there is a bit nasty looking. It's a reddish brown color and who knows how old. I forgot to mention (and I hope this doesn't turn out to be the issue) that I used some Teflon tape on the sending unit. The fans sure do work when they are on though. 260 down to 190 or so pretty quickly at idle. If the PCM reading turns out to be close to what I'm seeing on the gauge, does that mean the sending unit my be faulty?

 

I looked in the shop book. Looks like the fans are supposed to turn on around 212 degrees.

Odds are there is nothing wrong with the temp sensor since the PCM is getting a reading (those sensors normally don't fail). As for the teflon tape, should be no issue so long as it was ONLY on the threads of the sensor and not around the "probe" of it.

If the reading from the PCM on a ODB-II scan tool differs from the reading on the instrument panel, trust what the ODB-II reading is, as that's what the PCM is operating your fans on, that is what it's getting from your temp sensor. If that's the case, it's either the data stream from the BCM to the cluster is bad or something wrong in the cluster.

I dealt with a Grand Prix (never solved it) that the temp gauge spikes, but according to the PCM, temp is fine.

If the ODB-II reading says the temp really is 260 and the fans are not coming on, next is the question why. I believe the car is equipped with 2 fans and has a low and a high speed. It could be a case the low speed is not turning on, which then asks the questions is it not turning on because the PCM did not command it too or a fan is malfunctioning.

First thing's first, try to find out if the data from the PCM matches the gauge (otherwise you are going to go nuts chasing a problem that may not be).

 

Right on. I'll have to swing by a shop to get the PCM read. I'll look into getting my own scan tool though.

 

Any direction on what scan tool to get? Looks like I should get something that is updatable at least?