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Old 03-11-2013, 02:27 PM   #1
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How Hot is TOO hot?

Took my 1986 26' Itasca (7.4 litre 454 GM ) on a 320 mile round trip , pulling a 14" enclosed trailer, that turned out to be a big pain in the A#$. Left early in the evening and the weather was cool. About 70 mi into the trip I noticed the temp start to creep up around 230. I got a little more than nervous as I then watched it creep up to 250. I pulled over right away and shut it off. As soon as the engine stopped the needle jumps why up to ????? ( i dont know what because the temp gauge only reads 250.) I noticed then that the electric fans werent turning. I circumvented the thermostat circuit and made them run all the time. this seemed to cool it down pretty quickly. Got back on the road with it at about 190 deg. but within 25 miles it was headed back up to the 250 mark. So the next couple of hours went on this way. (BTW did i mention it was late by this time and I was in the middle of nowhere)
I decided it had to be a sticky thermostat , so I get up the next morning and replace it with a new 180deg. thermostat. Cut to us leaving on sunday and about 20 miles into the trip here we go again. !!! I finally figured it out. The fan clutch would disengauge about the time the temp would begin to climb. Faulty fan clutch "gotcha". So i descovered that if I kept the RV around 50 MPH it would run about 225 to 230 deg. Im knew to this so forgive me, I felt like this would be acceptable. I drove it for about 125 miles home this way. My question is could I have damaged the engine running it at this temperature? What should it run at idealy? I was exhausted by the time i got home so I havent looked at it yet, However it seemed O.K. till about 5 miles from home when I detected what may have been a little power loss. I might have just been a little paranoid too.
BTW i wasnt too worried about it until I started looking at the threads on here about all the nightmares from overheating. I wanted to read something that might make me feel better , but guess what, Im in full on panick mode now.
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Old 03-11-2013, 04:40 PM   #2
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Radiator time. If it's never been touched time for a rebuild or replace. Most of us here have been / were in, denile about it. Everybody's done something to try and prove otherwise but it appears to be radiator time with a declutching fan to boot.
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Old 03-11-2013, 05:17 PM   #3
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Have you had it flushed lately? My 87 Allegro would begin to overheat until we had it flushed and all belts replaced. The fan clutch would then kick in and no problems.
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Old 03-11-2013, 05:22 PM   #4
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1986 could be a few things.

Fan clutch
Bad Belt
Loose belt
Late timing
Thermostat
To start...

Loose Belt will get you, most folks fkex the Center of the span between pullies like the book instructs, but that is only part of it.

As the belt ages it gets glazed and looses reaction, simple test.

Grab the fins on the alternator pully and see if you can turn it.

If you can turn the pully without the motor moving the belt is slipping, if old replace, if new tighten.

Late timing causes fire to be exposed in the cycle where the heat goes into the walls instead of piston, it produces less power and polution.

If adjustable check it, sometimes loose vacuum hose will cause retarded timing.

Thermostat is easy, if the engine cools with increase of rpm then may not be stuck, they usually cause engine to get hot regardless.

If you can get it to where you can remove the cap you may be able to see water flow, but this is tricky so only as last resort

Fan clutch should have some drag, if it spins freely or wobbles it is toast, consider changing it, and belts just for good measure.

Search this forum for overheating and power loss, many of us have provided detailed instruction on how to resolve many problems.

Post your findings
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Old 03-11-2013, 05:28 PM   #5
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Regarding damage, as long as there was water flowing AND you managed to get it cooled down before shutting off you SHOULD be okay.

Turning off while hot may cause local damage from where the heat us sourced, keeping the water flowing helps dissipate the heat and if you can get it cooled down, shift it down and spin up the motor you are better off.

Have you confirmed actual temperature?

Get an IR thermometer, perfect for times like this, confirms heat levels and is non-contact, by scanning the radiator you can see if it is plugged, that area will be cooler than the unplugged spot.
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Old 03-11-2013, 05:47 PM   #6
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Originally Posted by BA-in-Mich View Post
Radiator time. If it's never been touched time for a rebuild or replace. Most of us here have been / were in, denile about it. Everybody's done something to try and prove otherwise but it appears to be radiator time with a declutching fan to boot.
I agree. It's time.
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Old 03-11-2013, 05:48 PM   #7
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Have you had it flushed lately? My 87 Allegro would begin to overheat until we had it flushed and all belts replaced. The fan clutch would then kick in and no problems.
I haven't had it flushed. Think I'm gonna just go through the cooling system from top to bottom and replace everything.
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Old 03-11-2013, 05:58 PM   #8
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Thanks for all the input guys. As far as my peace of mind goes I think I'm gonna replace the entire cooling system. From water pump to radiator. Just concerned that I may have done severe damage that's gonna get me after I spend big money replacing cooling components. I read a post where a guy says his overheated at 220 deg and scored the cylinder walls and had to replace the engine. His was new. Mines 27 yrs old. Just a little worried that ill get new cooling system and find out I blew my motor. Got a great deal on my RV and I knew she needed a lil TLC. Think I should e addressed some issues before I started using it.
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Old 03-11-2013, 06:01 PM   #9
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Regarding damage, as long as there was water flowing AND you managed to get it cooled down before shutting off you SHOULD be okay.

Turning off while hot may cause local damage from where the heat us sourced, keeping the water flowing helps dissipate the heat and if you can get it cooled down, shift it down and spin up the motor you are better off.

Have you confirmed actual temperature?

Get an IR thermometer, perfect for times like this, confirms heat levels and is non-contact, by scanning the radiator you can see if it is plugged, that area will be cooler than the unplugged spot.
Thanks for answering. Still what temp should these things run at safely.
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Old 03-11-2013, 07:19 PM   #10
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Thanks for answering. Still what temp should these things run at safely.
180-200 degrees ideally. But I have seen them run a lot hotter and be just fine. The plus side is you don't have aluminum heads or block. Another thing to think about is possible damage to the tranny from the high temps, but then again, I think you probably would have noticed within that distance.

If it was me, I would examine the oil and coolant first to make sure there is no cross contamination. Cross contamination is an indication of at very least a blown head gasket, or worse cracked head or block. Then, I would pull and examine the plugs. If they don't look burned or deformed, I would then run a compression test on the cylinders. Not sure what it should be, but it can looked up on the net. If all checks out, I think I would take the chance on putting the money into the coolling system. I think you are on the right track with wanting to replace it all. I had similar overheating issues with a 460, and it ended up being a combination of old, crudded up radiator, and old fan clutch. Like you, I decided I was only going to do this once. So I replaced the radiator (went from 3 to 4 core), clutch fan, water pump, thermostat, hoses, and belts all at one time. No more cooling problems.

Those old engines are almost bullet proof, and the 454 is notorious for runing hot, so I really wouldn't stress about it, but I would definetly check it out good.

I would also have the fluid changed in the tranny. You've cooked it. Heat is the #1 killer of trannies. I also added a tranny temp gauge just for peace of mind.
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Old 03-11-2013, 08:51 PM   #11
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180-200 degrees ideally. But I have seen them run a lot hotter and be just fine. The plus side is you don't have aluminum heads or block. Another thing to think about is possible damage to the tranny from the high temps, but then again, I think you probably would have noticed within that distance.

If it was me, I would examine the oil and coolant first to make sure there is no cross contamination. Cross contamination is an indication of at very least a blown head gasket, or worse cracked head or block. Then, I would pull and examine the plugs. If they don't look burned or deformed, I would then run a compression test on the cylinders. Not sure what it should be, but it can looked up on the net. If all checks out, I think I would take the chance on putting the money into the coolling system. I think you are on the right track with wanting to replace it all. I had similar overheating issues with a 460, and it ended up being a combination of old, crudded up radiator, and old fan clutch. Like you, I decided I was only going to do this once. So I replaced the radiator (went from 3 to 4 core), clutch fan, water pump, thermostat, hoses, and belts all at one time. No more cooling problems.

Those old engines are almost bullet proof, and the 454 is notorious for runing hot, so I really wouldn't stress about it, but I would definetly check it out good.

I would also have the fluid changed in the tranny. You've cooked it. Heat is the #1 killer of trannies. I also added a tranny temp gauge just for peace of mind.
Thanks , you've answered My question and given me a good direction to go. I intend do exactly as you've outlined here. I'm new to the RV world and it seems that there's a lot that doesn't transfer from automobiles. These things can be complicated and to make things worse the previous owners made a mess out of the electrical system. I have a hill to climb before it ever leaves the driveway again. But I'm told that these things can be fun. So hopefully it'll be worth it when I'm sitting in sturgis SD next year.
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Old 03-11-2013, 09:01 PM   #12
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My son was a tech @ GM proving grounds in Milford MI, Power Train Dept.
You need a full service, flush fluid (not just drain and fill) and new filter, on the tranny. Tranny fluid starts to cook @ 225. Anything higher has done the deed. Service now or re-build tranny later.
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Old 03-12-2013, 12:20 AM   #13
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The pressure capital alliws higher operating temperature, 3 degrees per pound.

This is to keep the water as liquid.

As long as there was water flowing and you hot it coolef down you should be okay.

Do check the oil, maybe change all fluids.

You can get a bore inspection camera from HF and look inside cyl through separate plug hole
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Old 03-12-2013, 12:47 AM   #14
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I had the same MH as you several years ago. I had the same symtoms as you described. The brakes were draging, turned out to be sluge in the master brake cylinder. After replacing the brake cylinder, all new fluid, bleeding, all was well. Because of the size of the engine, I really didn't notice, as there was penty of power, only ran hot. just another thought.
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