Overheating too quickly
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Posting Guru
Joined: Nov 2011
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From: Burlington, WI
Timing is set properly by ear. I do need to get verified by a light. Ill have to check my fan clutch after work tomorrow too.
When the engine is at its normal mid range temperature, the idling RPMS are set to be around 650 and it idles there. However, it does have "dips" where it momentarily drops from 650 to 500. Occassionally it will jump to 900...all without me touching the throttle while its idling normally...however short after these bursts or dips, the engine begins to get really warm...its like the idle speed or the carb in general is still a bit jagged up.
When the engine is at its normal mid range temperature, the idling RPMS are set to be around 650 and it idles there. However, it does have "dips" where it momentarily drops from 650 to 500. Occassionally it will jump to 900...all without me touching the throttle while its idling normally...however short after these bursts or dips, the engine begins to get really warm...its like the idle speed or the carb in general is still a bit jagged up.
Posting Guru
Joined: Oct 2007
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From: Sedro-Woolley, WA
I'm guessing now but the only thing I can think of that would cause those rpm shifts is fluctuations in your timing. Is the distributor vacuum line connected to the metered port on your carb?
Posting Guru
Joined: Oct 2007
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From: Sedro-Woolley, WA
Next time it heats up, rev the engine and hold it at about 2000-2500 and see if it cools down. If it does cool down then the problem could be too low idle rpms. If it doesn't then it is most likely the fan clutch isn't engaging properly and needs replacement..
Low idle rpms could be caused by something as simple as as the idle speed adjustment on the linkage or it could need a proper tune up.
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Posting Guru
Joined: Nov 2011
Posts: 1,302
Likes: 5
From: Burlington, WI
Ok folks I got some stuff to report.
Last night I checked my fan clutch. It is easy to spin cold and hard to spin hot. You can hear it kick in and change rpms with the engine running at different speeds.
I increased my idle rpms from 650 to 800. Made a small difference, but not much in terms of temps.
I will insulate my fuel lines tonight and maybe add my (rather large) carb spacer gasket too.
The ambient air temp today was about 80*. When driving through town, the truck stayed cool and the temp gauge was on the N. When driving on the freeway, it was the same...on the N and fairly smoother running.
When I got to Taco Bell and was waiting in the drivethrough, the temps went up to the R. I then parked the truck and turned it off to eat my lunch. Then when leaving Taco Bell after the truck sat in the sun, the gauge was at the M. It then dropped down to N once I got on the freeway and the truck became happy again.
Sooo...is this normal?? Dad wants to flush the radiator this weekend which I'm afraid may cause more leaks (already have a few pinholes)...any suggestions? Should I buy a new thermostat? The one in the truck has been replaced before but...you know how it goes with PO repairs...
thoughts????
Last night I checked my fan clutch. It is easy to spin cold and hard to spin hot. You can hear it kick in and change rpms with the engine running at different speeds.
I increased my idle rpms from 650 to 800. Made a small difference, but not much in terms of temps.
I will insulate my fuel lines tonight and maybe add my (rather large) carb spacer gasket too.
The ambient air temp today was about 80*. When driving through town, the truck stayed cool and the temp gauge was on the N. When driving on the freeway, it was the same...on the N and fairly smoother running.
When I got to Taco Bell and was waiting in the drivethrough, the temps went up to the R. I then parked the truck and turned it off to eat my lunch. Then when leaving Taco Bell after the truck sat in the sun, the gauge was at the M. It then dropped down to N once I got on the freeway and the truck became happy again.
Sooo...is this normal?? Dad wants to flush the radiator this weekend which I'm afraid may cause more leaks (already have a few pinholes)...any suggestions? Should I buy a new thermostat? The one in the truck has been replaced before but...you know how it goes with PO repairs...
thoughts????
Post Fiend
Joined: Mar 2011
Posts: 8,501
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From: Lynchburg, VA
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Posting Guru
Joined: Oct 2007
Posts: 1,144
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From: Sedro-Woolley, WA
What you just described is pretty much normal. Also what others are recommending about setting up an independent gauge is very good advice.
I would start looking for a replacement radiator too. Pinholes only get bigger.
I would start looking for a replacement radiator too. Pinholes only get bigger.
Cargo Master
Joined: May 2009
Posts: 2,587
Likes: 47
From: Eagle River, AK
Another thing to consider that is sometimes overlooked.
Your coolant system relies on building and keeping pressure and if the pressure is relieved (pin hole), your temps will increase. The pressure the system is designed to run at has a lot to do with keeping temps in check. That is why a leaky radiator cap can cause a hot temp situation.
Just my $0.02
Senior User
Joined: Mar 2013
Posts: 388
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From: Sandy Eggo
for what its worth, my temps were all over the place when i first got the truck. the factory gauge seemed to be hot one minute, cold the next. i replaced the thermo stat, changed the coolant and added a mechanical temp gauge, and turns out i was alarmed about nothing. the truck was running fine, right at 5* above whatever thermostat happened to be in it (i tried a couple different ones getting it tuned right). even something as simple as air bubbles in the coolant can cause fluctuation in the gauge, and the factory one sucks to begin with.
Senior User
Joined: Sep 2012
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It sounds like a fan clutch on the overheating, if you are not losing any coolant over time. Easy enough to "rent" the little pressure pumper thing from one of the chain parts stores- pump presure in the Rad and see how long it holds . I just replaced a fan clutch that I bought 4 months ago. it was "easy" to spin cold and "harder" to spin hot, but still it was not spinning well. of course, is your fan bolted on the right direction 
?
fluctuation in idle sounds like vacum leak- at least mine was doing that (76 f250 with 460) & after I replaced the old lines and 38 year old connectors, it idled fine
? fluctuation in idle sounds like vacum leak- at least mine was doing that (76 f250 with 460) & after I replaced the old lines and 38 year old connectors, it idled fine
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