Thread: Thermostat vs Moroso Washer

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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.

Originally Posted by MelloYello

.....,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.

Em,
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.