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Old 06-10-2015, 09:31 AM   #1
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454 inconsistent cooling/overheating

I have a 28ft Pathfinder with the standard 454 Chevy big block and normally aspirated engine. It starts and runs perfectly.

However, on the last trip, it would show normally mid way on the engine temperature guage unless climbing,,,,then

During one day it would seem to climb way into the red and then sometimes it would drop back down to usual temps during normal flat road driving, and without reason again intermittently climb way up to the red or past red area. I can't tell if this is real, a thermostat going bad, blockage somewhere in the cooling lines, or a defective guage?

Does anyone know what could cause this behavior?

Thanks
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Old 06-10-2015, 10:07 AM   #2
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My first thought would be the thermostat is sticking. Also, check the wire connection. Most 'mechanics' aren't too keen on electrical connections and sometimes overlook fried wires or loose connections when working around them.
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Old 06-10-2015, 08:45 PM   #3
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Smile 454 overheating

How long has it been since you have had your cooling system flushed? I would flush the system...use a premium antifreeze 50/50 mix and have the thermostat replaced at the same time. 454 are sensitive to overheating and you don't want to blow a head gasket. The fact that is heated up and then dropped back sounds like a thermostat but you can get a similar issue with a bad radiator cap as well. Make sure you get a radiator cap that is the right pounds of pressure for your application.
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Old 06-10-2015, 08:47 PM   #4
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It may be a bad temperature sensor. I would get an infiread temperature guage and check the engine block and radiator temp when engine operating at normal temperature and again when the guage reads hot just to see the difference. That will tell you if it is running hot.

Your findings will provide you of where the problem is.

Examples, hot block cooler radiator- thermostat.

Radiator cooler in some spots hotter in other parts - plugged radiator.

I hope some of this information is helpful.
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Old 06-10-2015, 08:54 PM   #5
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I second the infrared temperature gun it helped me figure out I had a bad temp sender on my 93 Class A 454....... If the radiator isnt boiling over and shooting water out when the gauge is pegged I would say its a bad temp or temp sending unit.I would change the temp sender first.
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Old 06-10-2015, 11:28 PM   #6
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We had a Winnie about that vintage. It's problem was a very fine tightly spaced radiator fin that would easily plug on dusty roads. Sometimes plugged into the middle and not visible to the casual look-see. I ended up having to occasionally wash the rad down on that particular stretch of road. Temps would go up with load and normalize on the flats.
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Old 06-10-2015, 11:41 PM   #7
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That engine has a clutch fan that should be pretty obvious, noise wise, when it engages. It should sound like a small plane taking off. Very common of the clutch to go bad. If you determine it to be the clutch, buy a new one from Chevy, not aftermarket. The quality varies too much.
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Old 06-11-2015, 12:09 AM   #8
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Inconsistent Cooling

Thanks for all the very good ideas.

I will flush the radiator, change the thermostat, and the fluid, then wash out th radiator for dirt etc....

I can hear the fans kick in just fine, so think they are ok...

Will post back if this plan of procedures does the trick.

Thanks
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Old 06-11-2015, 07:10 AM   #9
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The problem may just be a wonky temperature gauge and/or sender. I had the same issue on a '95 P-30 with 6.5 Diesel. I added an aftermarket temperature gauge & sender, and found the dashboard gauge (when it worked) was reading 20-30 degrees cool. I found the same discrepancy on our current '99 gas P-30 454 when I installed a scangauge. My conclusion is that the GM dashboard gauges are not too good.

Quote:
Originally Posted by Mt Class A View Post
I have a 28ft Pathfinder with the standard 454 Chevy big block and normally aspirated engine. It starts and runs perfectly.

However, on the last trip, it would show normally mid way on the engine temperature guage unless climbing,,,,then

During one day it would seem to climb way into the red and then sometimes it would drop back down to usual temps during normal flat road driving, and without reason again intermittently climb way up to the red or past red area. I can't tell if this is real, a thermostat going bad, blockage somewhere in the cooling lines, or a defective guage?

Does anyone know what could cause this behavior?

Thanks
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Old 10-01-2015, 07:36 PM   #10
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My 96 Winnebago P30 was running too hot on hills. I flushed and replaced the 195 degree thermostat with a 180 degree. Now it idles too high.
Can anyone tell me if this is probable?
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Old 10-01-2015, 08:41 PM   #11
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My 96 Winnebago P30 was running too hot on hills. I flushed and replaced the 195 degree thermostat with a 180 degree. Now it idles too high.
Can anyone tell me if this is probable?
It will. The computer is adjusting for a lower operating temperature and holding it in a fast idle condition. The system was designed to have a temperature of 195 deg. You will be adding fuel via the computer because the temp. is not up to normal running specs. 195 deg.
Too hot would mean the temperature was over spec. ( in your case 195 deg. ) changing a thermostat would not change anything. The 180 deg. thermostat would open sooner but the temp. would still climb because there is another problem within the cooling system. It might take a little longer but it will get there.

Lynn
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Old 10-01-2015, 08:51 PM   #12
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Quote:
Originally Posted by LETMGROW View Post
It will. The computer is adjusting for a lower operating temperature and holding it in a fast idle condition. The system was designed to have a temperature of 195 deg. You will be adding fuel via the computer because the temp. is not up to normal running specs. 195 deg.
Too hot would mean the temperature was over spec. ( in your case 195 deg. ) changing a thermostat would not change anything. The 180 deg. thermostat would open sooner but the temp. would still climb because there is another problem within the cooling system. It might take a little longer but it will get there.

Lynn
I agree with Lynn.....

There is some kind of misconception that going to a lower thermostat will aid in cooling.

Your engine was designed to run at 195 degrees, I am not sure why people try to make it run cooler, it is normal for it to rise when climbing hills.



if your cooling system could truly cool to 185 degrees then it would work.

but if your cooling system can only cool to lets say 195, then the 185 thermostat will stay open all the time.


Can you define "too hot"


I would look at your cooling system, radiator and cap, might need to flush the radiator, or clean the bugs and road grime from the fins, some simple green and a water hose on the engine side of the rad.


Does your fan engage, it should engage at about 210


My 454 runs between 200-210, the only time my temp rises is going up a grade, and then at around 210 I can hear the fan engage, which then brings the temp down to 200 and fan disengages.
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Old 10-01-2015, 09:55 PM   #13
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When you blast the radiator fins with a hose do it from the front and back. My 454 behaved exactly as yours and washing the fins of the radiator worked like magic. When I washed the fins from the front the problem remained, after washing the fins from the back towards the front, the engine never again overheated. The radiator did not look that dirty before I cleaned the fins and I was very surprised that this simple process fixed my problem.
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Old 10-02-2015, 04:59 AM   #14
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When you blast the radiator fins with a hose do it from the front and back. My 454 behaved exactly as yours and washing the fins of the radiator worked like magic. When I washed the fins from the front the problem remained, after washing the fins from the back towards the front, the engine never again overheated. The radiator did not look that dirty before I cleaned the fins and I was very surprised that this simple process fixed my problem.
I agree cleaning the radiator fins would be a good idea and may solve the problem. Be careful though. DO NOT use a high pressure washer. The excess pressure can actually flatten the delicate fins and make the situation even worse.
Try to get a look between the radiator and AC condenser. You might have to loosen and move the condenser ahead to thoroughly clean both.
A good vacuum cleaner works pretty well pulling debris from the condenser. Don't put a lot of pressure on the fins though. Again you don't want to flatten these fins out. Preferably use the vacuum before wetting the fins.
Lynn
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