Overheating - Cooling fan operation?

[ratedrookie]

Hello all, first post on this forum and I'm glad to have found an active GP community is still out there. I've been a member of other GP boards for over 10 years. I own a 2000 GTP coupe and I'm experiencing an overheating issue that I can't seem to figure out. After a lot of searching and trying several things, I'm about out of answers so I'm hoping for some help from this board.

For starters some background...

2000 GTP
141K miles
180 t-stat
PRJ intercoooler
3.2 pulley
1.8 comp pro mags
TOG headers
Tuned myself via PowrTuner
Various other supporting mods
LIM gaskets replaced with metal design at around 60K miles


I've been driving my car for many years and tens of thousands of miles under this configuration. The car has always run in the 170-190 degree range even idling in traffic on really hot days. The temp gauge never reached the halfway 210 degree mark.

A few weeks ago, the temps started going much higher than normal. It would hit 210 and more so I knew something was off. On a couple of occasions I've had to pull over as the gauge started to creep towards the 3/4 mark.

I started by examining the obvious by checking coolant level, t-stat, pump, leaks, etc...

I noticed that the temps seem to rise around town and driving in traffic, but looked fine at speed so I started to suspect that I have an issue with the cooling fans.

So far I have validated that both fans work by supplying battery power to them. With 12v directly from the battery, both fans spin at high speed.

I checked the 3 under-hood relays, one is a 5 pin and the two others are 4 pin and they all checked out well.

I swapped the ECT with the one from my other 3800 powered car.


What I don't understand is how the fans are supposed to operate on my car. Do they operate at different speeds? Is one a high speed and another a low speed? I noticed that the driver's side fan spins fast, but the passenger side fan spins very slow.

When I turn on the A/C, should both fans spin at high speed?

I have the fans tuned to kick on at lower temps vs stock since I'm using a 180 t-stat and I have validated that they do turn on, but once again, the driver's side fan spins fast and the passenger side spins slow.

I don't know if this is normal operation. If it is normal, what else could be the cause of my overheating issue?

Thanks!

[Scottydoggs]

water pump could be rusted to hell and not pumping anymore. seen that a few times.

[chibiblacksheep]

I've also seen the fins on the water pump completely go.

Both fans should spin relatively quick, and the AC should kick fans on.

[CHI2000GTP]

Yeah. Those water pumps literally dissolve. Here's mine from when I did the LIMs in January.... Just gone.

[Ridin ON Chrome]

I have similar mods and mine would not stay below 215*.

Turns out my 180 tstat was bad.
Now it will hover around 190-195* in traffic and dip down in the 180s which is all I except when it's 95* out with almost 100% humidity.

So I say bad T-stat or like pump like stated.

[ratedrookie]

Thanks everyone for the quick replies.

Both the radiator and water pump were replaced just a few years ago and probably only have about 10-15K miles on them if that. I also just replaced the thermostat with a new 180 degree a couple of weeks ago in trying to diagnose the overheating issue.

I will check the water pump again and test the thermostat just in case.

Both fans should spin relatively quick, and the AC should kick fans on.

The AC does kick on both fans but should both fans spin at the same speed? For whatever reason the driver's side fan spins fast but the passenger side is slow. It feels like it's barely pulling any air compared to the driver's side. I'm still not sure if this is normal operation of the fans.

[chibiblacksheep]

I have my fan system completely replaced because the stock fans didn't work with my CSC build. I can't check for you, but I'm pretty sure that they should both spin at the same speeds

[chris99gtp]

I'm in a very similar situation. When the a/c is on, the drivers side fan spins high but the other fan barely moves. On low they both turn fine. I've been told to check the ground. So I'm going to check that soon and then I'll post my results.

[J57ltr]

The way they are wired is that relay 1 switches power to both fans, but due to the way it's wired to the other relays the fans are in series. So both fans spin slow, since they only have half the voltage to each. When they see in high speed the other 2 relays switch state and wire each fan to full battery power. That's how they should operate. Now because your pass side can is slower it makes the other fan increase in speed because as the fan turns slower the back EMF is less which doesn't oppose the flow of current when it's running at speed. Basically your pass side fan sounds like it's going bad.

[ratedrookie]

The way they are wired is that relay 1 switches power to both fans, but due to the way it's wired to the other relays the fans are in series. So both fans spin slow, since they only have half the voltage to each. When they see in high speed the other 2 relays switch state and wire each fan to full battery power. That's how they should operate. Now because your pass side can is slower it makes the other fan increase in speed because as the fan turns slower the back EMF is less which doesn't oppose the flow of current when it's running at speed. Basically your pass side fan sounds like it's going bad.

I think I eliminated the fan motor itself as the culprit because I went ahead and replaced it with a known good motor, but same results. The passenger side fan still spins very slowly compared to the driver's side.

However your explanation makes me wonder about the relays. The relays have all tested good. Despite the tests, I have already replaced the 5 pin relay a couple of times with some extras I have but same results. I believe the 5 pin relay is the one you are referring to as the one that switches power to both fans.

I have not replaced the two 4 pin relays. I did swap the fan #1 and fan #2 relays around to see if it would make a difference but it did not. Based on the way they are wired, I'm wondering if any one of the two relays are bad, if the condition of the slow fan would persist? I don't know the answer but relays are cheap enough that it might be worth trying to just replace them both.

[J57ltr]

I would have to look at a schematic again to see exactly which one and how it's wired to give you a good answer. Since they are in series it makes no difference as current in a series circuit is always the same. Maybe your slower fan is wired different (more turns, lower rpm) than the drivers side fan. You should have enough air to feel air across your legs standing in front of the car. On mine at low speed both of my fans run the same speed. I have never gotten to the point of needing a high speed fan, but I have a manual turn on and I can hear it run from inside the car.

[ratedrookie]

Here's a schematic I found.

[J57ltr]

As relay 12 is pulled in and power passes through the first fan then back through the relays (9) normally closed fan then on to ground so 2 wired in series. When high speed fan is actuated relay 9 and 10 are turned on. Relay 9 pulls the right fan to ground and now has full power. Relay 10 then applies full power to the right fan.