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#1 |
Registered User
Join Date: Mar 2008
Location: Bynum, Tx
Posts: 21
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Overheating 72 3/4 ton 402
OK, I'm stumped. My 1972 Chevy 3/4 ton with 402 has begun overheating. I pull a 24 foot goosneck with a 4-6K tractor, mower on it. I have replaced the water pump, radiator (new NAPA 4 row brass and copper) and installed a 160 degree thermostat. It still goes to 230+ even on a mild day. Doesn't do much better w/o the tractor and trailer. It runs good, no miss or backfire. It will "run-on" after switched off sometimes when it's hot. It has a 400 auto with a 12"x15" trans cooler in front of the radiator on the passenger side and an auxillary electric fan pushing air on the other side. I also added a coolant recovery tank, set the timing to 8 degrees BTC. What am I missing? Could the trans cooler be blocking too much air? You guys are great with diagnosing.
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#2 |
Registered User
Join Date: Jun 2010
Location: Upland Ca
Posts: 4,143
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Re: Overheating 72 3/4 ton 402
If it just began to overheat with out any mods than that's good. It just means one or more of the components has failed. Did it start overheating before or after the rad and WP? How are you measuring the temp? If by gauge then you need to verify with an IR gun. Thermo does not affect high temp, just how fast it gets there. Do you have a good clutch fan? How about the fan shroud? I would bump the timing a few degrees and see if that helps.
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1972 C10 SWB, Air, PS, PB, 350/350THM. Second owner. 1965 Corvette roadster, 44K miles, 327/365 SHP, 4 speed, side exhaust, knockoffs, teak, second owner (bought in 1970), Have ALL numbers matching components. My frame off restoration thread: http://67-72chevytrucks.com/vboard/s...d.php?t=556703 |
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#3 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,643
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Re: Overheating 72 3/4 ton 402
Ditto these two questions... also, are you running 50/50 antifreeze/water?
As to 'dieseling' when shut off, leave it in gear when turning the ignition off, instead of neutral or park. Not a cure but it helps the engine shut down quickly.
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#4 | |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,643
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Re: Overheating 72 3/4 ton 402
Quote:
Whether you try that or go back to a clutch fan (my recommendation), I would definitely get a fan shroud if you don't already have one.
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay Last edited by Stocker; 10-18-2010 at 06:31 PM. |
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#5 | |
Old member
Join Date: Jan 2002
Location: Liberty, & Garden City S.C. , U.S.
Posts: 19,936
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1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 ![]() Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs. |
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#6 | |
Registered User
Join Date: Mar 2008
Location: Bynum, Tx
Posts: 21
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Re: Overheating 72 3/4 ton 402
Quote:
Stocker, it is 50/50 antifreeze and the electric fan is mounted in front of the radiator and is pushing air toward the radiator. It only operates when the A/C is on. Thanks for the help. I'll try the IR for temp. and keep trying. |
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#7 | |
just can't cover up my redneck
Join Date: May 2004
Location: Columbus OH
Posts: 11,414
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Re: Overheating 72 3/4 ton 402
When does it overheat?
Low speed (city) driving is usually an airflow issue High speed (highway) driving is usually a coolant flow problem. But, first you need to verify that you really do have a problem. Eliminate things like the possibility of an air bubble or the accuracy of the gauge.
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#8 |
Senior Member
Join Date: Jan 2003
Location: daytonabeach
Posts: 22,956
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Re: Overheating 72 3/4 ton 402
i'd take an oldschool tmermometer and put it in the coolant and see what the actual real temp of the coolant is before saying it was overheating and throwing parts at something without knowing for sure a problem exists
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71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY Last edited by cdowns; 10-18-2010 at 07:42 PM. |
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#9 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,622
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Re: Overheating 72 3/4 ton 402
Do you have a support coil in the bottom rad hose??
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#10 |
Registered User
Join Date: Mar 2008
Location: Bynum, Tx
Posts: 21
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Re: Overheating 72 3/4 ton 402
Thanks for the continued suggestions. Won't be able to try solutions until Sat. Don't know about coil in lower hose. Its pretty new,so I would think so. I've tried to purge an air pocket, but have not tried jacking it up. I'll keep you posted. I'llalso verify the tem reading.
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#11 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,622
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Re: Overheating 72 3/4 ton 402
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#12 |
Registered User
![]() Join Date: Sep 2001
Location: Fort Wayne, Indiana, USA
Posts: 1,887
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Re: Overheating 72 3/4 ton 402
Believe it or not, my gauge was lying because my voltage regulator was bad. I realized my gauge was lying when I used an infrared thermometer on the radiator. Replaced the regulator and the gauge read correctly.
Run-on/dieseling, makes me think you are overheating. If you have access to an infrared thermometer (some multimeters have them built-in), check the temp of the radiator tanks (left and right). You should see a significant drop (mine was inlet at 180 and outlet around 150). Low coolant flow would result in a higher than normal temperature difference in the tank temps. Low air flow would result in lower than normal temperature difference (bad clutch or plugged front). Fouling on the inside of the tube (not likely in a reasonably new rad) would also result in lower than normal temperature difference. Get some data and let us know what you find. Good Luck! |
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#13 |
Registered User
Join Date: Mar 2008
Location: Bynum, Tx
Posts: 21
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Re: Overheating 72 3/4 ton 402
Well, I'm back. Still no good news, but I think I have eliminated some things it's not. Changed the temp. gauge, let it run al loooong time to purge any air bubbles and bought an IR thermometer. Still seems to run too hot. Here's the data. After driving long enough to get the gauge to 230 I returned home and took measurements. Water temp gauge = 230+, Air temp.=80, thermostat housing =218, radiator tank at inlet =215, radiator tank passenger side = 200.
Next (last?) option is to replace fan clutch with a hd version. Current one is 2.5 yr old but doesn't make alot of noise. Another possible cause is the a/c condenser. Changed to 134a with new almost everything. A/C shop was concerned with high head pressure and installed an aux fan wired to the compressor. Could this generate enough extra heat to cause my problems? Thanks for all the help. |
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#14 |
Registered User
Join Date: Mar 2008
Location: Bynum, Tx
Posts: 21
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Re: Overheating 72 3/4 ton 402
I forgot-the bottom hose does have a wire coil inside.
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#15 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,622
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Re: Overheating 72 3/4 ton 402
Even though you replaced the WP and it was overheating before that did you put a WP in that was for an A/C truck. Those are made for more flow using a different impeller.
Second thought!! WP speed? Is your WP pulley stock? A smaller one could produce more flow. You have to watch not to speed your pump up too much though. You can cause the WP to cavitate which hurts flow too. And one more. Maybe you need to slow the flow down for more coolant retention time in the rad. Just some thoughts!!! |
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#16 |
Registered User
![]() Join Date: Sep 2001
Location: Fort Wayne, Indiana, USA
Posts: 1,887
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Re: Overheating 72 3/4 ton 402
The temperature drop across the radiator seems low. Where were you testing the inlet air temperature? If your A/C was heating the air too much or affecting air flow across the radiator, I could potentially see a problem. I also assume the fan that was added to the A/C system pushes air from the front of the condenser toward the radiator. If it is in the opposite direction, I would expect a problem.
Did you do the rolled-up newspaper test on the fan clutch (the fan should not be able to be stopped with a 5-6 page rolled up newspaper rubbing against the fan while running)? |
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#17 | |
Registered User
Join Date: Mar 2008
Location: Bynum, Tx
Posts: 21
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Re: Overheating 72 3/4 ton 402
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#18 | |
Registered User
Join Date: Mar 2008
Location: Bynum, Tx
Posts: 21
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Re: Overheating 72 3/4 ton 402
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#19 |
Registered User
Join Date: Sep 2010
Location: Los Angeles California
Posts: 352
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Re: Overheating 72 3/4 ton 402
My Barracuda overheated with a 160 thermostat..
At 160 the antifreeze was being allowed to pass through the radiator quicker, and not giving it ample time to cool. Once it gets 160 or higher, the thermostat stays open, and the radiator can't work as efficiently. I put in a 180, and it kept the water in the radiator longer to allow it to cool more. The higher temperature thermostat made my car run cooler overall. J.
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1972 Custom Deluxe Highlander C20 1971 Javelin SST New Project 1971 Demon 340 1969 SS El Camino 1968 SS RS 396 Camaro 1967 Barracuda Formula S 1965 140/4sp Corvair Monza Convertible Sorry, but I don't do Fords. |
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#20 |
Registered User
Join Date: Mar 2008
Location: Bynum, Tx
Posts: 21
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Re: Overheating 72 3/4 ton 402
I'm back. Only thing left (I think) is the fan clutch. Mine has a little leakage. Bought a heavy duty (hayden 2747) which is a little longer. Thanks for the help. I'll let you know if this does it.
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#21 |
Registered User
Join Date: Nov 2008
Location: Italy
Posts: 1,278
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Re: Overheating 72 3/4 ton 402
I just went thru a similar situation. Truck started heating up with less than 300 miles on a frame off build. All components are new. I swapped t-stats, flushed radiator, replaced lower hose, ect. I then removed the t-stat all together. When I did that it never got hotter than 150 while cruising. Closer observation turned up bubbles in the coolant. Looks to be a gasket or crack. Still need to tear it down to find out. Took me a week to figure it out. I have no water in my oil and the truck runs and sounds great. I was able to determine the problem using a combustion leak tester. You fill the tester full of blue fluid, connect it to a vacuum source, remove the radiator cap and snug it into the hole. If the fluid turns yellow you have a leak.
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'68 C-10 SWB 383 Stroker (Sold 3/2/2013) '87 R2500 LWB 454 TBI converted to Carb ![]() |
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#22 | |
Registered User
Join Date: Mar 2008
Location: Bynum, Tx
Posts: 21
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Re: Overheating 72 3/4 ton 402
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#23 |
Registered User
Join Date: Nov 2008
Location: Italy
Posts: 1,278
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Re: Overheating 72 3/4 ton 402
I picked mine up at O'Reilly's Auto Parts and paid around $45. I could have gotten it cheaper if I wanted to wait. It's $24.96 on Amazon. Check here:
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'68 C-10 SWB 383 Stroker (Sold 3/2/2013) '87 R2500 LWB 454 TBI converted to Carb ![]() Last edited by AusTx68; 11-02-2010 at 12:30 PM. |
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#24 |
Registered User
Join Date: Mar 2008
Location: Bynum, Tx
Posts: 21
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Re: Overheating 72 3/4 ton 402
Thanks for the info. If the new fan clutch doesn't fix the problem, that will be my next option.
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#25 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,643
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Re: Overheating 72 3/4 ton 402
I'd bet the new one will fix it, since the old one was leaking... I've been mistaken once or twice in my life but I hope this isn't one of those times.
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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