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| Virginia91C4 | Yet another Cooling Question | ||
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Guru Newb
 
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Hi Guys!
My first post, and new Guru user so be gentle lol. On my 91 L98 it runs hotter than I would like even though I've read they run a little hot from the factory. My problem is I grounded the two connectors on the computer diagnostic connector under the dash like you would to pull trouble codes and both my primary and secondary fans both power on as they should, they also both come on with the AC engaged. Problem is I never hear the primary fan come on ever under normal driving or in traffic, and the secondary fan comes on when the gauge reads 250+, and at that point the fan never catches up to cooling it down. My question is since the fans both come on in diagnostic mode does that mean the relays and fan circuit are ok and I should look at the coolant temp sensor as being the problem. I have a new all aluminum 3 core radiator on the way because the old one is in pretty bad shape anyway. One last quick question. How long will I own my new Vette before I quit looking outside and drooling at it? |
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Posted on: 2012/6/23 0:17
Edited by Virginia91C4 on 2012/6/23 0:34:52 |
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| BillH | Re: Yet another Cooling Question | ||
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The Stig Moderator
 
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Welcome to the forum.
I don't have the spec for a 91 but on a 92 LT1, the primary fan turns on at 226 and the secondary turns on at 235 (but LT1's run hotter than a L98. Before, you change the sensor, run the car at fast idle, hood open and see for yourself when the fans kick on. 250 is too high, so it's possible it's the temp sensor. Check for debrie BETWEEN the a/c condensor and the radiator. What temp are you running on the highway? |
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Posted on: 2012/6/23 1:51
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| Virginia91C4 | Re: Yet another Cooling Question | ||
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Guru Newb
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Thanks for info! I did check for trash between the condensor and radiator, and didn't see much and removed. I did verify with the hood up that the primary never comes on ever, but the secondary comes on seemingly late at 250ish. On the high way as long as I keep moving at a good clip the gauge stays in a good range guesstimating because no numbers on gauge but around 210-220 on hot day. But as soon as I lose air across radiator it climbs slowly stays up near 250 or so.
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Posted on: 2012/6/23 2:20
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| Matatk | Re: Yet another Cooling Question | ||
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The fans on 1990 and up are ECM controlled. 250 is too hot to start turning on, though. Which gauge are you reading the temperature from? I recall one (ie analog vs digital) is not as accurate, but I don't remember off-hand which one.
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Posted on: 2012/6/23 3:12
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| Virginia91C4 | Re: Yet another Cooling Question | ||
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Guru Newb
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I don't remember seeing a digital temp gauge, but it might have one. I will have to look, but I think its all analog except speedo. I do remember the analog water temp because it has a number at the bottom 120 i think, and 260 at the top and not much in between. Yes 250 is to hot for me too for the fans. I'm thinking the coolant temp sensor isn't giving a high enough signal to trigger the primary fan. And the only reason the secondary comes on (too hot) is a safe guard through another circuit or something (scratching head).
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Posted on: 2012/6/23 3:31
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| BillH | Re: Yet another Cooling Question | ||
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The Stig Moderator
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Look for the button under the trip monitor that says "gauges"
It will put the water temp up on the lcd seedo screen. The analog gauges are usually way off, |
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Posted on: 2012/6/23 4:13
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| bogus | Re: Yet another Cooling Question | ||
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Grand Imperial Pooh-Bah
 
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welcome!!!
 250 is way hot... I would bet money that between a nasty radiator and a lot of debris, you have found the cause. These cars are bottom feeders, which means they get their air from down low... which turns them into large Hoover vacuums. Leaves, feathers, entire birds, cigarette butts, plastic bags and wrappers... it can get ugly. And if its never been cleared out, well, yuck. Be ready to hose the radiator housing out thoroughly before installing the new rad. What rad did you get? |
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Posted on: 2012/6/23 6:45
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| Ultraman | Re: Yet another Cooling Question | ||
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2015 Memorial Day Car Show Winner!
 
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A big welcome to the Guru......the answer to your last question is.......never.....
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Posted on: 2012/6/23 9:26
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| Matatk | Re: Yet another Cooling Question | ||
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Webmaster
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Quote:
Thanks for clearing that up. Check the digital gauge - it is more accurate. If I recall, as well, there are two different temperature sensors - the digital one (more accurate) uses the PCM coolant temp sensor (located in water pump?) and the analog one uses a separate sensor in the head. I think the position of the sensors make a difference. |
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Posted on: 2012/6/23 11:47
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2002 EBM convertible, Magnusson supercharger, cam, headers, etc. 1989 Corvette...RIP |
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| Churchkey | Re: Yet another Cooling Question | ||
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Guru
 
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91 may have a "range" button same as the 90, no "gauges" buttom. (unsure about 91 dash)
The analog gauges on my 90 read high. Suggest checking radiator in out temps with a digital hand held pyrometer to compare to the dash gauge. Or you can monitor the upper radiator hose. As soon as it gets hot when the thermostat opens see where the temp gauge is sitting. It will probably indicate 3/4 hot. Fans do not run when vehicle speed is 55+ mph. Main fan should cycle at 228* without the AC on. If memory serves the temp trigger switch for the main fan is located in the thermostat area. Will check later to verify. Switch in right head (exhaust manifold area)is for temp gauge. Main fan runs when AC is selected? It should. Coolant temps will actually be lower when the AC is in use. I use the AC mode to keep it cool in traffic. For summer operation: Suggest connecting the 2 fan relay ground wires together. Relays are grouped together, left side of fan shroud.I use male/female insulated spade connectors. Both fans run when AC is in operation or 228* engine temp is reached. Jumper wire is disconnected for cool weather operation. |
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Posted on: 2012/6/23 13:11
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| BillH | Re: Yet another Cooling Question | ||
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The Stig Moderator
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Quote:
Yea, you're right Church, I had a fuzzy web pic of the 91 dash when I posted that. They added the gauges button in 92. +1 on veryfing the actual coolant temps. The analog on my 92 reads way high. David, you need to get a Factory Servive Manual if you don't already have one. It's a "must have" for working on a C4. |
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Posted on: 2012/6/23 13:26
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| flyboy | Re: Yet another Cooling Question | ||
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Elite Guru
 
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"If the engine is actually overheating and the gauge indicated overheating, but the cooling fan is not coming "ON", the Coolant Temperature Sensor (CTS) has probably shifted out of calibration and should be replaced."
This is from the '91 FSM and sounds like your problem. The CTS is under the throttle body in the front of the intake manifold base. No "gauges" button or digital readout on a '91. This is where a Tech 1 would come in handy to check the accuracy of the dash gauge. My gauge needle is just past the middle at about 200*F. |
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Posted on: 2012/6/23 13:31
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'91coupe, LT4Hotcam, some other stuff. If it's too loud, you're too old. "He works on old cars, then junks 'em" |
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| Virginia91C4 | Re: Yet another Cooling Question | ||
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Guru Newb
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Wow, thanks to all of you for the valuable info. Yes confirmed today, GM cheated me out of the gauges button and gave me a range button instead, not a fair trade off. Yes I was reading about how the analog temp gauge can not be accurate, especially if the temp sensor in the passenger side head has been change with one thats not a genuine gm part. So I was from the beginning thinking maybe the car wasn't as hot as the gauge showed. I'll just try a digital thermometer and try to confirm the temps.
Agreed Reno (thanks), a shop manual would definitely be in the list of things to get going on the project, I wonder if the Haynes that advance auto parts would be decent. Sounds like flyboy (thanks) is kinda pushin in my direction with the coolant temp sensor, For the price thats not much money for good first try at fixing the problem. I guess I won't drive it much until my radiator gets here tuesday, I would hate to have a preventable melt down do to a low price part. |
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Posted on: 2012/6/23 15:40
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| bogus | Re: Yet another Cooling Question | ||
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Grand Imperial Pooh-Bah
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I don't recommend the Haynes for service, but I do suggest it for photo's. The C4 is just to complex to cull down to a single 200 page guide for all 14 years of the C4. It just does not work.
Check this link for the manual on CD: http://www.ebay.com/itm/1991-CHEVROLE ... d8&vxp=mtr#ht_1144wt_1037 |
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Posted on: 2012/6/23 15:44
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The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
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| Virginia91C4 | Re: Yet another Cooling Question | ||
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Guru Newb
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By the way I've had a lot of cars and always wanted a Vette, so I love the car. The only thing I don't like so far is the way the 4sp automatic overdrive is. I think its a 700r4. Anyway the over drive is working ok I guess, It just seems all about gas mileage in that gear and it comes in a little to early for me @35mph or so under light pedal. It just sounds like it bogs so bad in overdrive.
Ok cool on the manual, i'll check it out. Yeah haynes sometimes leaves out a lot of stuff along the way. |
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Posted on: 2012/6/23 15:48
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| bogus | Re: Yet another Cooling Question | ||
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Grand Imperial Pooh-Bah
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They played games with the EPA by getting the 700R4 to shift into OD quick like that. Yea, it does load the engine, but there is enough torque to beat it out. If the trans isn't shifting right, check the TV cable. I don't have pics available, but it's this D shaped thing on a cable, coming off the throttle body and heading to the trans. Using an open end wrench, push in the metal button inside the D shaped part, push the cable all the way tight, then, WITH THE ENGINE OFF! - pull the throttle until it can go no more. That will reset the TV cable.
If you decide to keep the car, swapping over to a 6spd is doable, but expensive. |
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Posted on: 2012/6/23 16:00
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_________________
The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
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| Churchkey | Re: Yet another Cooling Question | ||
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Guru
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Quote:
When I had the 89 auto I found that it was crisper around town using "3" instead of OD. Select OD when cruising @ 45+ MPH. |
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Posted on: 2012/6/23 16:07
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| Virginia91C4 | Re: Yet another Cooling Question | ||
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Guru Newb
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Ok thanks God-Like, Ill check out the cable adjustment.
Yes Churchkey I tried the keeping to third gear thing, definitely feels more like want. My cars kinda quiet at this point, I bet it sounds bad with loud pipes when you bog into OD like that. |
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Posted on: 2012/6/23 16:15
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| flyboy | Re: Yet another Cooling Question | ||
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Elite Guru
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My chip was reprogrammed to shift into OD(4th) at 50mph.
Much nicer. |
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Posted on: 2012/6/23 16:18
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'91coupe, LT4Hotcam, some other stuff. If it's too loud, you're too old. "He works on old cars, then junks 'em" |
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| Virginia91C4 | Re: Yet another Cooling Question | ||
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Guru Newb
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Thats probably what I'll do down the road, reprogram the chip. I'd probably go 45-50 as well on the OD. Maybe also change the fans to come in a little earlier once I get them working right anyway. It seems the obd1 computers these year GM's have don't have a lot to play with like obd2. I wonder how much power could be added and not losing to much mpg.
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Posted on: 2012/6/23 16:25
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| bogus | Re: Yet another Cooling Question | ||
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Grand Imperial Pooh-Bah
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the L98 has 2 real performance issues... the intake and the exhaust.
You can pick up 100hp by doing the following: roller rockers headers dual exhaust dual bullet cats (pass sniff!) performance intake manifold Seriously. 100hp. |
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Posted on: 2012/6/23 22:36
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_________________
The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
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| Virginia91C4 | Re: Yet another Cooling Question | ||
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Guru Newb
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Ok, I changed the coolant temp sensor and yahoo, that at least kicks one fan on at what looks like 250, but I think the gauge is wrong. Im going to try a genuine gm temp sender for the gauge and see what happens.
Is the Larger of the 2 fans the primary? If so thats the one thats coming on now and stays on until it cools down some. So the smaller of the two is the one that comes on last at the higher temp? Because I never saw that one come on yet without the AC on. |
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Posted on: 2012/6/23 22:39
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| 1Fast04Vert | Re: Yet another Cooling Question | ||
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Elite Guru
 
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Sounds normal. Primary fan comes on about 227*F, but the secondary doesn't come on until about 236*F. |
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Posted on: 2012/6/23 23:32
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| flyboy | Re: Yet another Cooling Question | ||
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Elite Guru
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On a '91, both fans are identical. Left side fan mounted higher on the radiator is the primary one.
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Posted on: 2012/6/24 3:05
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'91coupe, LT4Hotcam, some other stuff. If it's too loud, you're too old. "He works on old cars, then junks 'em" |
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