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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / December 2005Truck runs too cool - how to diagnose the problem?
96 Chevrolet 4.3L V6 C1500 This is a continuation of the Thermostat thread I had started earlier: http://groups.google.com/group/rec.autos.tech/browse_thread/thread/58f6f4e5e0541 65a/fbae8f5686c7cfb2#fbae8f5686c7cfb2 My truck runs too cool. I have installed a new 195 thermostat and tested it by heating it in a pan of water. It opens at about 199, closes fully at about 190. I installed it and then from a cold engine start, the temp gauge rises to about 196, then drops quickly to 165, in which neighborhood it stays at while driving. The top radiator hose is cool to touch until the temp guage reaches the 195 point. Then it gets pretty warm, but really not too hot to touch as the temp gauge goes down to the aforementioned 165. From this point on I can stick my finger in the radiator water (don't try this at home : ) and it is like bath water. So it seems that it really is running cooler than 195... It looks to me like the thermostat and temp sending unit are working. I am gonna block the radiator and see if the temp comes up on the gauge- if it does, that should confirm that the gauge and sender are working. What else could make it run cool? I see the fan clutch (is a mechanical type, not electrical) appears to be always engaged - would this cause it? Thanks, Libby The only thing I can think of is a bad thermostat. Maybe it went in the wrong way or hung up on the gasket? I just had to change mine because my gauge didn't rise above the start of the green and it was freakin cold inside. Mine was one of those 'failsafe' thermostats that I managed to make fail last summer by getting it hot without boiling over the rad. It failed open. So I put the 195 in and got great inside heat with the top rad hose hot once the t-stat opened. Mine has stayed there. It doesn't cool off below the 190 you noted as fully closed for the thermostat. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Aug./05 http://www.imagestation.com/album/index.html?id=2120343242 (More Off Road album links at bottom of the view page) > 96 Chevrolet 4.3L V6 C1500 > This is a continuation of the Thermostat thread I had started earlier: [quoted text clipped - 20 lines] > Thanks, > Libby > 96 Chevrolet 4.3L V6 C1500 > This is a continuation of the Thermostat thread I had started earlier: [quoted text clipped - 20 lines] > Thanks, > Libby The only thing that would let your engine run cool is a bad thermostat. Period. if u are looking for more heat bacflush the heater core with a garden hose and make sure the water pump is not leaking « Paul » wrote: > > 96 Chevrolet 4.3L V6 C1500 > > This is a continuation of the Thermostat thread I had started earlier: [quoted text clipped - 23 lines] > The only thing that would let your engine run cool is a bad thermostat. > Period. I have put in 3 different thermostats this week. I heated each one in a pan of water before installing. Each of them do not open until around 195 - 200, and close back again at around 190. I can state definitively that it is not the thermostat. I also replaced the coolant temperature sensor, and the temperature guage sensor, after testing each before installing. It ain't either of them either. The truck temp guage climbs to 195, the thermostat opens, top radiator hose gets hot, then the temperature guage drops to the 165 - 170 range. Then the guage begins to rise again, then drops, fluctuating between 170 - 195, but staying mostly at the low end. At this point I think the coolant system and guage is ok, I think maybe the fan clutch is constantly engaged which perhaps makes it impossible to maintain the high operating temperature. My heater is nice and hot so no problem there. I just wanted the truck to run at 195 as it is my understanding that if the motor doesn't run at the mfg spec temp, it will carbon up more quickly and also be less efficient. Libby In article <1133648030.075181.130530@g49g2000cwa.googlegroups.com>, > I have put in 3 different thermostats this week. I heated each one in a > pan of water before installing. Each of them do not open until around [quoted text clipped - 20 lines] > > Libby Where are you getting the thermostats from? I've had very good luck with Stant super stats, otherwise, OEM if a super stat isn't available. A constantly engaged fan clutch will make a roaring noise, some fan clutches roar when the engine is first started but then quiet down after a mile or so, this initial roaring in my experience is usually reserved to 3/4 and 1 ton trucks... A stuck fan clutch will kill your fuel economy. Make absolute certain that there is no air in the system. Make absolute certain that the intake gaskets aren't leaking. make certain that you have the correct water pump, there are forward rotation pumps and reverse rotation pumps available for the 4.3 depending on whether it uses a serpentine belt or V belts as accessory drives. Was the heater hose quick connect fitting in the intake manifold ever swapped out for a straight hose fitting? The quick connect contains a restrictor that if absent -could- mess with the volume of coolant by-passing the thermostat. I did swap out the quick connect this summer, it had corroded and broke off. The one I replaced it with was from Auto Zone and allegedly was the right one for the truck. Is it possible it doesn't have the bypass you mentioned, or maybe has the wrong one? > Make absolute certain that there is no air in the system. Some people in the past have recommended drilling a small hole in the thermostat body, away from the moving parts and sealing surfaces, to allow an eventual airbubble to pass through easily. This subject came up again recently, and the website concluded that it was probably a good modification. (If so, why didnt the manufacturer do it?) I cant see that it would really hurt anything. Have you ever done this, and if so were you satisfied with the results? > Have you ever done this, and if so were you satisfied with the results? I've only replaced a handful of thermostats in my day (all Ratsun) but they've all had holes in them already. The install instructions were always clear to put the hole at the "top" of the thermo to allow bubbles to pass through. Cheers, Geoff Glave Vancouver, Canada > I have put in 3 different thermostats this week. I heated each one in a > pan of water before installing. Each of them do not open until around [quoted text clipped - 20 lines] > > Libby It really sounds like the thermostat is not closing properly. While they are not instantaneous, they are reasonably quick to close. Try a different brand. |
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