Near-Overheat, and passenger fan refuses to run

[Myotis1134]

Two problems here:

 

1. Recently tore the engine (1991 3.1) down, pulled the back head off to stick an oversize thread repair insert in the most passenger-side spark plug hole. Reassembled with new gaskets and temperature sending sensor (the one in the head). Busted the EGR tube while putting it back together, and eventually bought a '92 4-door euro for what I would have paid for a new tube ($300). The new euro (helga) reluctantly donated her EGR tube to the cause, and I got it all reassembled last weekend.

 

Filled the radiator until full, as well as the reservoir tank, and started her until she overheated. Bled, filled, and restarted with the heater on full. To make a long story short, there is plenty of coolant, but the engine keeps getting hot - the needle on the gauge stays between the beginning mark on the last quarter, and the bottom of the first red bar. it fluctuates back and forth. I changed the thermostat, but it kept doing it. When the driver-side fan finally turns on, the temp drops very quickly, but the damn fan hardly ever seems to come on, but that's problem 2. The radiator is new, and all the hoses and sensors associated with it. When I first put the new radiator in, I had problems with the overheating, but that was because I hadn't bled it enough. After figuring that out, I had no problems with overheating up until this recent surgery.

 

2. This problem is related to 1, in that maybe if I can figure out what the hell is wrong with the fans, problem 1 will be eliminated when they work regularly. When the car is running, and the temp gets really high and stays there for a while, the driver-side fan will occasionally kick on for about 30 seconds at a time. I have stood over it and watched, and I have never seen the passenger fan come on, but when I jump the connectors to pull engine codes, both fans come on. So I know the damn thing works, it just doesn't when it's supposed to.

 

Browsed a few posts, and it seems that the possibility that the water pump is pooping out is, well, a possibility. The problem with this theory is that the whole cooling system worked just fine before I pulled the engine apart. I need some advice on shit to replace.

Edited August 11, 2011 by Myotis1134

[GnatGoSplat]

Sounds like classic symptoms of air in the cooling system. Some of them are a lot harder to bleed than others. Squeeze the upper radiator hose with the cap off to make sure there's no air still trapped.

[Myotis1134]

So what are the alternatives for getting ALL the air out of those systems? I came across a post in which someone was talking about a vacuum pump they hook up to maybe the overflow hose, attach a shop vac, and suck the air out. Dunno, looked it up on amazon and it's $80.

 

This whole situation is weird- I have fluid coming out of both bleeder valves, and I'm not sure what to do next. I squeezed the shit out of both hoses, and while squeezing the lower hose caused the fluid to drop a little, it really wasn't much and it's still overheating.

 

I hate to say it, but I'm thinking about finding a quick-lube or something like that, and seeing if they have a setup for forcing the air out.

[Myotis1134]

Ok, since I haven't had to deal with an overabundance of input on this (thanks to gnat for contributing of course), I have done some homework, and this is what I've discovered. Nearly a year ago, I got a subscription to alldata diy.com. Basically an online manual, but with more information and up-to-date specifics on things like part pricing, etc. The best thing about the site is that my manual is dedicated to MY specific car, year, and engine. Moving on.

 

I checked out the cooling fan system, and it seems that there are three main parts, the fans themselves, the relay circuits in the fuse box, and the temperature sending unit. If any of these three go bad, the fans won't run, but if either the fan motor, the circuit relay, or any of the wiring in between the two go, then the fans can't run. Period. If just the temperature sending unit (plugged into the head) goes bad, then the fan's can work, just not when they are supposed to.

 

The fans are supposed to kick on after the thermostat opens, but before the overheat light comes on. Any failure to do so, suggests that the temperature sending unit is bad, since it provides resistance to the circuit- which decreases as the heat rises. Once the heat rises sufficiently, the resistance from the sensor is weakened to the point where the fan relay circuits are able to send power to the fan motors, which run until the coolant has been cooled to the point where resistance once again becomes high enough to stop the circuit from completing the connection.

 

The problem I'm having is that my fans almost never come on (that I can see), so I didn't know specifically where the problem was in the system. When I jumped the 1 and 2 connector on the obd1 connector under the dash, the program that causes the trouble codes to flash on the gauge cluster also causes both fans to turn on, so I knew that the fan motors and wiring was ok. When I did this after pulling out the circuit relays (one at a time), neither fan would run while missing it's circuit relay, which suggests that (at least to some point) the relays are ok. The only thing left in the system that has influence over the fans running is the temperature sending unit.

 

I'm about to replace the brand new temperature sending unit, with an old, used one. If my logic is correct, then I somehow got a heat sensor that is not working like it's supposed to, which happens from time to time. According to the alldata diy site, the temp. sensor is supposed to be torqued to 22nm, and it's possible that I over-tightened it when installing, who knows. And how exactly are you supposed to torque something with a wire hanging out the backside? By eyeballing it I suppose.

 

Anyways this is my latest hypothesis of why my car is overheating. I was drawn to this conclusion by the fact that my radiator, thermostat, coolant hoses, and all related sensors are new, not to mention the coolant has been removed and replaced two different time in the near past. I recently removed the back head, and therefore everything else required to get to it, and reassembled with new gaskets. Before the tear-down, the cooling system worked perfectly, which kind of rules out the water pump.

 

I'm putting all this down in case the temperature sending unit doesn't correct the problem. I'll be back on in a few hours to report my success or failure.

Edited August 14, 2011 by Myotis1134

[Myotis1134]

Solved. After replacing the new temperature sending unit with an old one, fan kicks on when temperature gets near 3/4 mark on gauge. I'm guessing I got the wrong part, but serves me right for going to O'Reilly without knowing the exact part number. Still don't know the conditions that the passenger (auxiliary) fan needs to run, but I'm wondering if I can splice it into the primary fan's wiring to get enhanced cooling. Next project- find out where steering fluid leak is coming from.

[GnatGoSplat]

:thumbsup:Glad you figured it out!

[hrhoward]

Hello,

I have a '95 Regal 3.1. I also noticed that the pass. fan rarely comes on. I did get it to come on once when the temperature wasn't stupid hight. The the relay for the passenger fan out while the drivers side was running (a/c on) and the passenger fan wasn't. When I put it back, the passenger fan started and ran until I turned the car off.

 

Odd.

[Mel87]

From what I see on mine, the passenger side fan only comes on when the car runs hot (sitting in traffic) and the driver side fan ONLY comes on when the A/C is on. I don't know if my car has a faulty thermostat but this is the temp my car runs normally (constant moving/high way driving)

 

 

When the car sits at a dead stop for more than 5 minutes it was go up in temperature just before the white tick mark before the red zone, then the fan will kick on and cool it back down to where it is at in the picture.