Fluctuating Temperature Gauge (and other) questions

**gingerdude** · 12-14-2016

I have a 2001 Grand Prix SE with 43,000 miles on it, it has the 3100 engine with the 4t65E transmission. It was my grandparents second car and it was hardly ever driven. It was garage kept and is in great shape.

I would like to preface that my previous vehicle was a 1994 Grand Am with the 3100 and the 4t60 transmission, so I already know all the quirks of this drivetrain. This means I have done the intakes, head gaskets, water pump, hoses, thermostat, removed dex-cool, etc. Basically the entire cooling system has been revamped because it sat with dex-cool in it for 15 years. I've also done all fluids, filters, plugs, plug wires, oxygen sensor. Essentially any engine or transmission related stuff that you would replace after 15 years of sitting I have done.

I have a few questions about this vehicle.

1) My first question seems to happen in the summer. The temperature gauge will come up to the first large mark (195f according to my scan tool) and sit there while I am driving. If I sit and idle for awhile the gauge will creep up to the 210f mark (actually 225f according to the scan tool) and then quickly sink back down. The cycle will continue for as long as it sits. I know this is when the fans kick on. However before I did all of this work, I don't remember the gauge ever creeping up like that. (Now granted I only had the car for a month or so before I tore into it, so for all I know it did do this and I just didn't notice.) I also didn't see this happen with my Grand Am either. Is this normal for this vehicle?

2) My second question is similar, but is happening now that it is winter. The gauge will come up to the 195 mark, but while I am driving/idling in city circumstances the gauge will drop a few small tick marks down from 195, then swing back up a few tick marks above 195. This cycle also continues back and forth. The heat in the car seems to feel the same. If I get on the highway it stays constant 195f. My first thought was "hmm some air in the system..." So I popped the bleeders on both sides and no air came out. I am stumped. Again I don't remember this on my previous Grand Am, but this is the first winter with this car and it is super cold right now. Is this normal?

3) I know people on here say these N/A engines tend to knock pretty heavily. I am seeing up to 10 degrees of KR at WOT. This isn't going to damage my engine right?

4) I have a random misfire at idle. I have tried everything suggested. Cannot pin it down. I swapped ICM and coils, still present. When I pulled the fuel rail I tested each injector, they all OHM out properly and their spray patterns were perfect. Cleaned and checked for holes EGR. I used propane to try and find a vac leak. Nothing. Any thoughts?

**Fivefingerdeathpunch** · 12-14-2016

1. Pretty normal for a good working cooling system. The first fan will run at around 214-216º and then the second fan around that 225º mark thus bringing the cooling temp right back down. Some cars do this more on the regular than others. Perhaps a little lack of coolant flow could make it happen sooner for others, like a partly clogged radiator but it's hard to say for sure.

2. Again somewhat normal, it's just the thermostat opening and closing and causing the temps to jump around. Again some cars do it a little more than others. The temp sensor could be seeing a little air here and there or is just more sensative. Not every car acts the same way it seems.

3. On a NA with 87 pump gas, I'd say that is the common theme with those motors. If you pumped some 91+ octane fuel in there I bet it would cut it in half. They make the calibrations with having knock in mind, they have done it that way forever and see do it to this day in new cars.

4. Lower the plug gap .005 if worth a shot. I feel the factory gap is too large sometimes. If you put non AC Delco Iridium plugs in the cars then I'd look at that too. The waste spark ignition systems on these cars do not like platinum plugs.

**gingerdude** · 12-14-2016

I have AC Delco cheap coppers in there.

**gingerdude** · 12-15-2016

I'm not looking to have a performance car by any means. Just looking to have a reliable daily driver that will get me though maybe another 6 years. My Grand Am is still going at 170K miles, so I know these vehicles can make it if they are looked after well.

**gpbastard** · 12-25-2016

As for the temp gauge going up then down, mine does the same thing. It didn't do it until after 100k miles. I believe two things are happening here. The radiator is getting clogged up. Kind of like an artery. I think the reason for this is because of the lower intake manifold gaskets. They start going bad on these almost from the start. when they start leaking it turns the dex cool to mush. I would consider getting some new lower intake gaskets put in there with the new upgraded ones. If you don't do it yourself a shop will charge about a thousand bucks for this.
As for the knocking sound that's normal. A few years ago GM put out a tech service bulletin (TSB) on these 3.1 engines and said this is normal and won't shorten the life of the engines.
These engines take an Ac Delco 41-979 double platinum if I'm not mistaken. Don't run coppers in this engine. they're made to run these platinums. I would replace the plugs and wires on it along with the LIM gaskets. Autozone sells some great wires for this engine for 22 bucks a set and they're US made. If you want this engine to run it's best don't just throw any old spark plugs in it. This is important.

**gingerdude** · 12-25-2016

I did the intakes and head gaskets with the FelPro "PermaDry SevereDuty" kit, aka the metal ones. I also flushed the system and run green antifreeze now. Should be good there. I drove this same drivetrain in a 94 for 6ish years, so I'm aware of all the gasket issues. In the previous car the shop did them and they always used the plastic ones. It had to be redone like clockwork, so I decided with this car I'm doing it myself and bringing out the big guns (metal).

Alright I'll swap out for the platinums and see if that cleans up my idle. It has new wires on it, but they are from Advance.

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