85 720 radiator replacement with A/C

[saltlick]

I want to put a 3 core radiator in my 85 720 4x4. It has A/C too. I'm not sure what to get or where to find one that fits. Any ideas? I live in the mountains and have to climb a lot and it gets on the warm side.

[Charlie69]

I put a replacement aluminum with plastic tanks in my 96 2wd king cab.  In phoenix if I run the AC it runs warmer than it did with the stock copper core radiator.  Take your stock radiator to a radiator shop and have it re-cored with a 3 core core.  Down here in Phoenix this will run about $350.

Edited October 13, 2018 by Charlie69

[weldingrod]

Before you do anything expensive why not try a radiator flush?

[datzenmike]

Usually falls into one of these two...

 

 

Lack of air flow...

1/ Clutch fan silicone oil leaked out and fan 'free wheeling' and not turning fast enough.

2/ fog lights, dirt, leaves, debris blocking the cooling fins or fins deteriorated

3/ belly pan missing.

4/ shroud missing

 

Lack of coolant flow...

1/ slipping loose fan belt or pulley

2/ soft lower rad hose collapsing from pump suction when revved

3/ rad inner cores plugged with scale from using garden hose 'hard water' to top up rad

4/ block filled with scale and rust from not using antifreeze mix.

5/ heater hoses joined together to by pass leaking heater core.

 

Other....

Head gasket is failing.

Brakes draging

Engine out of tune (ignition retarded or one set of plugs not firing)

 

 

 

[bottomwatcher]

Well there can be a few other causes. I just replaced my radiator today because in spite of a nice clean flushed interior the salt air has desolved the fins to powder. Powder does not dissappeat  heat. 150 from autozone. Frigging Chinese and the lower tube was about six inches off but it was better than what was in the truck. Second radiator in 30 years we will see how this one lasts.

[Charlie69]

The replacement radiator I purchased was a 1 core 1" tube single pass aluminum radiator.

 

My next radiator for AC will be an all aluminum 2 1" tubes, double pass radiator with aluminum shroud and dual electric fans.

[datzenmike]

12 hours ago, bottomwatcher said:

Well there can be a few other causes.

 

Indeed there can be, including a faulty sender that reads high or an owner's perception of what constitutes 'gets on the warm side' really is. All engines get hotter when they do more work.

[bottomwatcher]

Chasing a gauge issue now. Engine was boiling over while still in the good zone on the gauge, sender reads 33 ohms. Should be between 20-40 ohms so that's good. Tested thermostat with meat thermometer in boiling water, opens right at 180 degrees. With the new radiator now runs just above the cold mark.. Soooo time to chase the ground. Battery voltage reads 13.8 while underway so somewhere along the way I am losing some voltage. 12 volt systems 95% of the time it is the ground or the ground or the ground. I am guessing this time it is a ground! Anyways after install the autozone radiator actually fits pretty well and is cooling well, that was in 90 degree Florida heat today.

[datzenmike]

The temp and gas gauges run on their own voltage regulator. It's about 8 volts so the gauges will read the same if the engine is stopped 12.6 v or charging 14.5v. If the gas gauge is wildly out then the voltage regulator for both is suspect. If you ground the sender wire to the intake (ground) the temp gauge should go all the way full hot. If it doesn't, then the gauge may be bad.

 

The temp sender grounds to the intake under the thermostat cover, not far from the battery ground cable.

[bottomwatcher]

Thanks for the tip! I have had issues before with the gauge reading high when applying voltage load via accessories while the engine temp remained the same. Running the fan on high while in the heat position should cool a warm running engine, anyways thanks for the gauge test. Will give it a go tomorrow. 

[Charlie69]

You are correct Mike but Phoenix is a bit hotter year around than BC.  We are surround by the Sonoran Desert not water.  Engine temp is real important to desert dwellers.

[saltlick]

Thanks for your advice everyone. I live in the desert of Nevada and have to climb the Sierra passes a lot up to 8,300 ft, sometimes I go places higher. My truck normally runs with the temp gauge at about half. It doesn’t get hot at idle, and it’s never actually overheated, but I’m paranoid it will when climbing/under load. By “on the warm side”  I mean it goes up to 3/4, and that’s too high for my tastes. Don’t know if it would go higher, because I end up turning the heater on to suck hot air off the engine. In 100 degree weather that’s just a drag! I can’t even use the A/C when the weather is hot because I don’t want the truck to get too hot (not the end of the world, but I’m not a young gal anymore so a little comfort would be nice!). I’ll have to have the radiator flushed and see what condition it’s in. I, unfortunately don’t know how to work on cars, although I’ve done shocks, wires, etc. Given that, it’s not the best truck for me because it is some other issues as well, but I can’t afford anything else. It’s a cute truck though and at 154,000 I hope it will keep going for a while. I’ll have other questions that I’ll post on other threads in regards to the carb, vibration and so on. Thanks!

[datzenmike]

Hmmm. My L20B runs at half and maybe a needle width higher when hot. I removed the clutch fan and now have two electric fans from a Subaru and a sensor and relay. This is preferable to turning the fan when not needed during warm up and when out on the highway. They turn on at 3/4 and move way more air than the original fan at low engine speeds.

 

 

Try something...

 

With the engine off grab the plastic fan blades and try to turn them. It should move but be quite firm. If you can spin it easily or it turns after you let go the clutch fan coupling fluid has leaked out. It's like a torque converter in an automatic transmission, it transmits power but there is enough slip to idle in gear when stopped. One side is the fan blades and the other side is turned by the fan belt. Motion is transmitted by the water pump through the viscous fluid to the fan blades. Fan speed maxes out at about 1,800 rpms no matter how fast you go. The 720 clutch fan has a thermostat that senses when the rad starts to over head and opens a valve letting in more fluid which in turn increases the drag and speeds up the fan blades to about 2,300 RPMs.

 

Here's the inside...

 

If that yellow oil has leaked out the fan will slip and not draw enough air through the rad. Years ago someone filled one with grease but it spins too fast and sounds like a jet taking off.

 

 

[saltlick]

Hmm. Come to think of it, the truck fan is a bit loud and has been since I bought it about 5 months ago. I mean, I like the sound, it sounds like a semi-truck when you hear the fan winding down. I thought it was just normal for the type of truck, but I had an 81 Toyota truck once and it never sounded like that. Maybe the fan clutch is bad. I'll try to turn it like you said and see what it does.

[datzenmike]

If roaring then it's moving air, and that's a good thing. If the bearing is seized inside it will move way more air than needed, still good though just noisy. 

 

Clutch fans are used to save gas by reducing the speed out on the highway, but if reduced too much, cooling is affected. It's probably OK, if loose you won't hear as much. Today's vehicles use electric fans. Vehicle speed pushes air through the rad so hardly on except idling at the lights.

[saltlick]

Radiator place took a very quick look and there was a little oil on the fan clutch so they recommended starting there.

[Charlie69]

On 10/14/2018 at 6:09 PM, bottomwatcher said:

Chasing a gauge issue now. Engine was boiling over while still in the good zone on the gauge, sender reads 33 ohms. Should be between 20-40 ohms so that's good. Tested thermostat with meat thermometer in boiling water, opens right at 180 degrees. With the new radiator now runs just above the cold mark.. Soooo time to chase the ground. Battery voltage reads 13.8 while underway so somewhere along the way I am losing some voltage. 12 volt systems 95% of the time it is the ground or the ground or the ground. I am guessing this time it is a ground! Anyways after install the autozone radiator actually fits pretty well and is cooling well, that was in 90 degree Florida heat today.

Has the block been flushed?

[datzenmike]

11 hours ago, saltlick said:

Radiator place took a very quick look and there was a little oil on the fan clutch so they recommended starting there.

 

Spin with your fingers. It should turn with some small effort like stirring a jar of honey with a spoon. It should not spin easily and it definitely shouldn't continue to spin when you let go. This built in slippage sets the maximum fan speed and the air that can be pulled through the rad by the engine.

[saltlick]

Yes it seems fine in that sense. It has about as much resistance as you describe. But a guy at the radiator place said there’s fan clutch fluid on it so he said it should be replaced.