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Help - I have a 302 GMC six cylinder that is overheating when cruising or after negotiating multiple stoplights. I have changed fluid, put in new 160 degree thermostat (it didn't have one before) added two bottle of water wetter, left my electric fans on all the time and it still gets too warm. My fans are ahead of the radiator. I have read that they should be behind the radiator but there is not enough room as the GMC motor is longer than the Chevy six.
Any ideas out there?
Is this a new project? Was it running fine before? Was it running ok when the temps were cooler?
Are the fans true pushers or did you just turn the blades around? Running a t-stat is a better way to go then using a reducer washer.
You sure the t-stat is opening? ...............What temps are you seeing? how hot is it?
use a infra red temp gun and take readings top, center and bottom of radiator core @ operating temp. You should see fairly even temps, If not core could be plugged.
I'm sure the t-stat is working as it gets up to normal temp pretty quickly where it didn't before when it had no t'stat. Thank you for the advice on running a t-stat vs a washer. It normally runs 180 down the highway but when I stop at multiple stoplights it will get up to 200 and then I shut it down. It only takes about 10 minutes to cool down and it has never boiled over. It did quit running once which I attributed to vapor lock. I have since insulated the fuel line to the carb and haven't had that situation again. There is air going through the radiator from the fans so I assume they are pushers. It did run cooler when the temp was lower. I guess I will just leave it in the garage when it's over 80, LOL. Just kidding, I drive this car a lot and love to be in cruises and would really like to solve this situation. I have been advised to modify the hood latch and make more room, put a fan behind the radiator and try that. I have also been told the heat gauge may not be accurate??
I will check the temps with an infra red gun. Thanks for the advice, didn't think of that.
Maybe GMC's just run hot? Anyone else out there know what is normal for a temp?
There's nothing wrong with a 20F gain to 200F in traffic, and 210F or 220F is not a worry if it's stable and drops back down to your controlled temp when you get moving again. Pusher fans mounted out front are at a disadvantage, as they are only putting air through 40% to 50% of the radiator surface (assuming 18"x24" surface, one 16" fan yields 46% area beneath the fan), while a puller fan with a proper shroud uses 100% of the surface. I'd say drive it and forget it, assuming your radiator core is clear, your water pump is good, and your t-stat is working.
I just finished dealing with a similar problem on my 289. I installed a new 190 t-stat, shroud and 6 blade flex-fan and solved the problem. My location is SE Texas and the dog days of summer also. Now it will idle under the carport at 190. I didn't notice what year your Jimmy was but is there room for a shroud in your set up? If so, I highly recommend it.
Also, when my t-stat opens the temp drops to 170 and then eases back up to between 185 and 190.
Em,Quote:
Originally Posted by MelloYello
On a mechanical fan or a puller electric mounted to the back side of the radiator a shroud is a necessary part of the cooling solution. However, on a pusher fan a shroud mounted in the front is going to block off about 50% of the radiator surface from direct velocity head (pressure from the car pushing into the air), and will severely restrict air flow through the radiator. A pusher fan runs without a shroud to allow maximum unrestricted air flow running down the road, and the fan mounted tight to the radiator to push air through the fan area when stopped, or moving slow in traffic.
Check your voltage at idle with the fans on, your alternator may not be large enough to keep up with the fans current demand causing a voltage drop, which in turn slows down the fans.
Roger, I was assuming that he understood my situation was all from the back of the radiator when I mentioned flex-fan - - certainly wasn't suggesting he put a shroud in front of the radiator - should have be more clear - - - sorry.
Something I will relate to all about what temp gauge is telling you:
Most temps sensors are located on or near the top hose outlet to the radiator. So as the coolant comes out of the radiator and makes its way inside the motor, it's removing heat from inside. Consequently this makes the coolant hotter, but it also leaves internal metals cooler. So as the coolant goes up past the sensor, it may register a hotter temp depending on how much heat the coolant absorbed. So now as it passes the sensor it will be at it's hottest point. This coolant is LEAVING the motor!! You are not gauging what's in the block, only the hot coolant temp on its way to the radiator. 200-210 is not hot and as long as the temps cool down once you start moving, you have nothing to worry about.
First of all, I would like to express my appreciation for all the answers given by my fellow hot rodders about my overheating situation.
I have taken all your advice to heart and will try some of the methods you suggest.
Thank you again for your help.
Maybe I am worrying needlessly (my wife says I do that about everything). I thought 220 degrees would damage my motor!! At the cruise the other night, a lot of cars were overheating and some of the guys would leave and drive down the highway a ways to cool the motor off. Mine has never boiled over but one time the engine died when it was hot. I assumed it was vapor locked. 10 minutes later it started and ran fine. I have since insulated the fuel line to the carburator and haven't had that situation again. I really don't want to remove my thermostat and replace it with a Moroso washer like some suggest. It now runs so much better as it warms up quickly and I don't have the idle problem like I used to have before the thermostat was put back in.
I'll be the bad guy here and suggest that if you had engineered the swap correctly in the first place, you wouldn't be having problems. The correct way to do it would have been to modify the core support so that you could have mounted the radiator slightly forward and used an OEM engine-driven fan and a close-fitting shroud. I've seen way more electric fan installations that didn't work than I have seen that did work and the ones with the fan in front of the radiator are the worst of the lot. The factory makes electric systems work, but they have highly-paid professional engineers who know how to do it.
And in the name of all that is holy, please guys, stop installing these fosdick 160 thermostats, hoping that they will cure your improperly engineered mess. Motors need to run ~195/200 degrees in order to burn off acids and other by-products of combustion that pollute the oil. Take a tip from the OEM's. Did you ever see a 160 thermostat installed from the factory????????????
I'm with Richard on this one..... Electric fans and water pumps are great on a drag car, makes for a quicker cool down between rounds---Then, as with many other things designed for racing, someone decided they would work on the street!!!!!
IMO there is no substitute for a properly designed cooling system incorporating an engine driven fan and water pump along with a fan shroud!
I don't think you are a bad guy at all. I wanted an answer to my problem, and this sounds like the one I will go with. I was told by a so-called expert to put the 160 degree t-stat in. Should I change it to a 180?
Imo the lower temp stat gives the engine a head start in keeping the cool, but once the motor begins generating more heat than the radiator can dissipate, that advantage is gone.
Maybe plan to change it out when the summer heat reduces.
The motor's thermostat only controls the minimum operating temperature of the motor, the radiator and fan(s) control the maximum temps. Lowering the motor's thermostat will not prevent (or even help) the motor from overheating, keeping the motor cool is the radiator and fan(s) job. And at best a lower temp thermostat could only add a few moments head start before the overheating returned. As mentioned earlier, if you are using a pressure cap and the correct coolant mixture 220° at idle is well within operating temps, without worry.
Also, there are other things that can cause a motor to run warm at low speeds, incorrect ignition timing is one, voltage drop due to an imbalanced charging system is another, air escaping around the radiator and not being pushed through it is yet another (this is critical with pusher fans).
IMHO, Pusher fans while not as efficient as puller fans can still be effective for cooling if sized and wired correctly, I run two pusher fans in California heat and they cool my motor even running A/C. But beware, properly sized pusher fans draw heavy current loads and may require upgrading your charging system.
No, you should change it to a 195. Get a meat thermometer (kitchen tools section of the local grocery store). Drop your thermostat into a pan of water, along with the probe of your meat thermometer. The thermostat must be totally covered with water. Turn up the heat and watch the temperature where the door begins to open on your thermostat. You must do your due diligence with every part you buy, that's why you want to know for sure where the thermostat opens. TAKE NOBODY'S WORD FOR ANYTHING.Quote:
Originally Posted by bubbiecars
Some fellows will drill a 1/8" hole out towards the edge of the thermostat to allow air to escape as you are going through the routine of filling the system with coolant.....not a bad idea in my opinion. Put a stainless steel spring in the bottom radiator hose to prevent it collapsing and cutting off cooling water to the motor. Yes, a good water pump can suck the bottom hose flat and make the motor run hot.
And don't use some cheap-ass 3 or 4 dollar "poppet" type thermostat, no matter who made it!
Get yourself a "sleeve" type thermostat, usually priced 7 to 10 dollars, this style will actually modulate to keep the engine at a constant temperature.
The poppet style is simply open then close and cannot flow what the sleeve type can.