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Old 09-28-2006, 12:55 PM   #1
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1988 34.5' Airstream 345
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New question about an old overheating problem on my 345

Well thanks to all for the good advice..I put my rig together and replaced everything in sight. I originally thought my fan clutch on an '88 345(with a 454) was causing my overheating problems. When I started the engine the fan would already be engaged and stay on or never come on at all. In the process of replacing that clutch fan, I replaced the water pump, therostat, hoses, belts, flushed the main radiator, removed the air conditioner radiator, increased the size of my oil and tranny coolers... I even rewired the electric fans to give added air flow... I started the engine no leaks, no sounds, runs great...but...I am still running warm at around 205 -215 range...talk about frustration....I have even re-examine the parts list with the dealer to make sure I bought the correct parts... I don't seem to be using any fluids or losing any power...but maybe I have a bad head gasket?....searching for advice..Mr.D.
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Old 09-28-2006, 06:06 PM   #2
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A couple of things come to mind.

1. You flushed the radiator. Sometimes flushing will not do it, the radiator may need to be rodded out to manually remove internal deposits in it.

2. Have the cooling system pressure tested. This is a very simple procedure where the system is pressurized to operating pressure, then search for any coolant leaks. If the system won't hold pressure due to leaks, the coolant will boil at a much lower temperature. This can be as simple as a radiator cap replacement.

It may also be something more serious ($$) like a head gasket or cracked head. I hope it's a rad. cap.

Good luck.
Dave
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Old 09-28-2006, 06:55 PM   #3
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New question about an old overheating problem on my 345

Greetings Mr. D!

While my experiences have not been with motorhome applications, I have had elusive temperature problems with three different GM big block V8s. If your motorhome has an exhaust heat riser valve, it could be causing such a problem if it is either operating erratically, rusted in a partially open position, etc. The first time this happened to me, I added a new timing chain and gears to your list of parts replaced as well as a new high capacity radiator before the exhaust heat riser valve was inspected and found to be frozen in a 75% closed position.

Good luck with your investigation!

Kevin
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Old 09-29-2006, 07:48 PM   #4
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My recommendation is to get a laser temp gun ,the econmical ones are not too expensive ,and can be used for any temp reading s on anything. Get the engine to operating temp ,then point the gun and shoot ,so to speak .check the top tank temp on the radiator ,then the bottom tank ,also the core itself.
Is it 200 at the top and 135 at the bottom ? (example temps),that right there can indicate a plugged radiator core ,they will block from the bottom up
and can really be plugged ,you would be surprised .If your temps are hot
all over the radiator top ,bottom etc say 205 degrees then it could be a head gasket ,the fan clutch should be coming in at 180 degrees ,the fan should be roaring with airflow ,unless the core is blocked and the sensor spring on the front of the clutch will not "SEE" the temp and not engage
the fan clutch .Make certain the clutch is a motorhome fan clutch as they
are very beefy looking .That 454 should run at 220 230 (bad) if it has a head gasket problem ,you can get a block check (combustion leak in cooling system) at a reputable radiator shop before any heads come off .

Good hunting on the trouble

Scott
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Old 09-29-2006, 08:58 PM   #5
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The temp gun is a great idea. I have one and use it all the time. You may just have a guage that is reading high. Someone may have put in the wrong sender.
Good luck, Rob
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Old 09-30-2006, 01:11 AM   #6
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Running Hot?

Quote:
Originally Posted by Mr. D
Well thanks to all for the good advice..I put my rig together and replaced everything in sight. I originally thought my fan clutch on an '88 345(with a 454) was causing my overheating problems. When I started the engine the fan would already be engaged and stay on or never come on at all. In the process of replacing that clutch fan, I replaced the water pump, therostat, hoses, belts, flushed the main radiator, removed the air conditioner radiator, increased the size of my oil and tranny coolers... I even rewired the electric fans to give added air flow... I started the engine no leaks, no sounds, runs great...but...I am still running warm at around 205 -215 range...talk about frustration....I have even re-examine the parts list with the dealer to make sure I bought the correct parts... I don't seem to be using any fluids or losing any power...but maybe I have a bad head gasket?....searching for advice..Mr.D.
Hi, How did you determine the temperature was 205 - 215? If you are looking at a dash gauge with numbers on it, don't trust the gauge to be that accurate. Use an infra-red temp gun. 205 - 215 is not that bad. I will explain later in this post. Next, never trust a radiator flush or boil out. Have it rodded out or replace it with a new one. [And new means new, not new to you, used.] Radiators do get clogged tubes. They start with a slight build up until completely blocked off. If your radiator has top and bottom tanks and the top tank is a lot hotter than the bottom tank, that usually means the fan is doing its job. Hot out of the top of the engine into the radiator, cooled by the fan, therefore cooler on the bottom. If you have side tanks, same thing, only uppper hose connected to the tank with the cap on it is the hot side and the one connected to the lower hose is the cold side. Partially clogged radiators usually run O.K. in town but overheat on the freeway because they cannot cool fast enough at higher speeds. If you can touch the front of the radiator while the engine is running and feel random hot and cold areas that is a good indication of a clogged radiator. With A/C condensor in front of radiator, you can't do this.
Basic cooling system theory taught to me at General Motors mechanic's school.
Water boils at 212 degrees F. 212
Add three degrees for every one pound of radiator pressure.
With a fifteen pound cap, add 45 degrees. 45
Next, and only with pressure, add 30 degrees more with-
-proper 50/50 mixture of Antifreeze / Coolant. 30
This totaled gives you the potential to run up to 287 degrees
before boiling over.
Note: Unless your engine actually boils over and pukes coolant into the street, it is not overheating, no matter what the temp gauge reads!

Bob
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Old 09-30-2006, 09:59 AM   #7
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Hi, Mr D. I would suggest that you take the radiator to a radiator shop with a flow test machine. This will tell you if the gallons per minute through the radiator is up to specs. If not, they can remove the tank and rod it out. Flushing will not always remove the hard stuff. Radiators dont wear out. For the 10 degree rise I would bet on the radiator.
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Old 09-30-2006, 11:25 AM   #8
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Hi, Mr D. Don't forget your thermostat. Heat water and put thermostat in with a thermometer to see when it opens. How is the radiator cap??? Good luck
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Old 09-30-2006, 12:35 PM   #9
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Mr. D.
A lot of good advice already. Keep in mind that motorhomes do run hotter than other vehicles. In fact the P30 manual I have recommends engines run at 195 degrees for "complete combusion". That said a few things can be done to manage your temps.

First I completely agree that you need a real tempature check at the thermostat, and the upper and lower hoses. The gauges on our units can give false readings.

Your fan clutch coming on at start up is normal. It should cut out after a minute or two then come back on to cool the engine. Note the temp when it comes back on at idle to draw air. Also note if this begins to drop the temps. The AC electric fans are good for adding air, but only the mechanical fan has the CFM needed to significantly lower engine temps. If it lowers temps and cuts out then it's managing the heat and working correctly.

Some people have had luck dropping in a 160 degree thermostat. I have one sitting in my glovebox right now to replace my 180 stat.

You may also consider adding a wetting agent from a parts store such as TowKool or Water Wetter. This will increase the efficiency of your cooling system and can lower temps 10 - 20 degrees.

Obviously the biggest issue could be a clogged or partially clogged radiator. Given the age of our units and the reality that many POs did not maintain their cooling systems it is very possible that you need a recore or replacement.

Check your spark plugs. Are they showing signs of lean mixture? This would increase your engine temps. Check your timing and make sure it's set correctly.

If you are concerned about a head gasket, do a compression check and look for contamination in the coolant and oil. You would also notice a "mystery" loss of coolant.

Lastly, most of us run in the 200 - 210 range with our motorhomes. It's not comfortable but it's a reality of the cab forward design with a 454 running all out most of the time in a confined space. In fact, my 454 is happiest on the highway at about 190 then increases around town to 200 - 210.

Keep us posted.
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