1986 C10 with 350 - running warm or not?

[mcintyrederek]

Hi,
I have a 1986 C10 with a plain-Jane Goodwrench 350 crate motor, a TH400 trans, and a 2.73 rear end.  It originally had a 4.3 V6 in it.  Someone else did the swap to a 350.  Everything else on the truck has over 200K miles on it.  It once had A/C but had been removed.  The condenser coil is still in front of the radiator, and the radiator is probably the original and probably never been taken out or serviced.  The fan clutch works properly, and the fins are straight and pretty clean.

Now that it's hitting the low 90's here in eastern NC, I am noticing my temp on the rise.  Today I am riding along at 45-55 MPH and seeing my temp fluctuate between 180 and 190.  I put a 180 stat in there (it had a 195 - seemed too high) but it's always ran between 170 and 180.  Just to see if the stat was running a little warm, I removed it completely.  Lobbing along again, driving easy and just cruising, I am hitting 175 to 180 degrees. 

I would like to pull a trailer with a total combined weight of 2500 - 3000 Lbs. a few times per year and running on an interstate (running 60 to 65 would be nice) for a 100 miles or so.  But I am certainly afraid to do this with it running 175 to 180 just cruising with no load.  The trans. cooler is built into the radiator, and the last thing I also want to do is get the trans. fluid too hot.

Does this seem a little high to you, running with no stat at all and still hitting up to 180 with the outdoor temp at only 85 to 90?  Do I need a bigger radiator, or get this one cleaned out?  Would putting an external trans. cooler on this truck also be a wise idea if I am going to be towing a little?

Thanks for your suggestions.

[SomeTexan]

Sounds fine to me. 230 is overheat, 210 I start keeping an eye on it wondering what's up. I had the best luck running a 195 t-stat in my small blocks. Seemed to keep temp more stable. If it gets over 210 towing, pulling a couple degrees of timing out may help.

[Captkaos]

195 stat running around 190 is normal.  Using a 180 stat and running around 180 is normal..

[mcintyrederek]

Thanks for the replies.  I'll try towing a short distance and keeping an eye on it before I go for the long haul.

What about the transmission?  If the water temp is 180, I'm assuming the trans. fluid is about the same since the trans. cooler is built into the radiator?  Is an external trans. cooler recommended for a TH400 towing?  Or is 180 degree trans. fluid OK?  I have no idea how much slip the torque converter has.  Someone told me they would recommended a converter just for towing that only had 5% slip.

[bd]

Personal Opinion:

Since you think the radiator has never been out of the vehicle, check with a local radiator shop to verify the radiator has adequate heat rejection characteristics for a 350 power plant* used for towing, then send the radiator out for a rod out and repair or replace it as needed.  (BTW - clean fins in a 1986 that has never been serviced is difficult to believe, unless it's been parked since 1987).  Remove the unused A/C condenser and install a 195° thermostat with fresh "green" coolant and 16 oz of LubeGard 96001 Kool-It additive.  Don't forget to test the radiator cap to ensure it will maintain ~15 PSI of cooling system pressure.  While it's apart, check the water pump weep hole for evidence of coolant seepage and replace it too if there are visible coolant tracks or accumulated silicate residue around the hole.

Regarding the transmission, install the most effective cooler that will fit in front of the radiator.  If space is limited, use a stacked plate cooler such as a B&M 70274.  Be sure to secure the cooler directly to the radiator support or a fabricated metal frame - do not mount the auxiliary cooler to the radiator core using plastic ties (even though the plastic ties are supplied with many coolers).  Plumb the auxiliary cooler into the existing trans cooler return line between the factory wet cooler and the transmission inlet.  Fluid flow should be through the factory cooler, then the auxiliary cooler, then back to the tranny.  If the trans fluid is not bright red, consider replacing the filter and fluid, now, upgrading to either Transynd full synthetic fluid (manufactured by Castrol for use in Allison automatics) or use mineral TCI Max Shift Street and add a bottle of LubeGard 60902 ATF Protectant.


* Edit - A quick search showed that the 4.3 V6 came with a 20.75"H x 17.25"W x 1"D radiator core, whereas the 350 V8 used a 28.25"H x 17.25"W x 1.25"D core.  It would be prudent to at least verify that they upgraded the radiator when they swapped the engine....

[rich weyand]

It sounds like everything is fine to me.  And a 3000 pound trailer is nothing.  It more depends on the wind-drag cross-section of the trailer.  Is it a horse trailer, a travel trailer, a camper trailer, what?  Square-cornered or rounded?  We pulled a lot of trailers in the last 45 years, round trips to Colorado, pulling in the mountains, even to Alaska when the Al-Can was still gravel (yes, stop the water, both ways), and cooling wasn't an issue until you had a heavier trailer with a large drag cross-section and were pushing hard in hot weather.  100 miles at 65 is an hour and thirty minutes, 100 miles at 55 is an hour and forty-eight minutes.  Why the big hurry?  The air starts to turn into a brick wall for drag at about 60.  Just take it easy if it's over 90 degrees out.

On the tranny, I'll second bd's suggestion to go to a synthetic ATF.  Tranny temps will come way down, because synth ATF reduces inefficiencies in the internal hydraulics, which gives greater horsepower transfer with reduced losses.  All of those losses turn into heat in the ATF that needs to be dissipated in the cooling loop.

[mcintyrederek]

Thanks again for the replies.  I will probably invest in the additional trans. cooler and mount it with a custom frame right in front of the radiator where the old A/C coil was.  I will also consider the synthetic ATF.  I am assuming you shouldn't mix new synthetic ATF with old fluid, so that means I need to drain the converter, too.

I am not pulling anything large, just a 16 foot flat trailer with a small farm tractor and implements.   

[rich weyand]

I am not pulling anything large, just a 16 foot flat trailer with a small farm tractor and implements.   

Then you don't need to do anything special at all.  That will all be in the drag shadow of the truck.  You should hardly even know it is there.  I've pulled those at highway speeds all day long with as little as a 2.3 liter E-class Mercedes.  You can put on the trans cooler if you want, but it's a waste of time and money IMO for that application.  In contrast, running synth is cheap.  You do have to drain everything, fill it with synth, run it a few miles to stir it all up, drain it again, and then put in the synth again, but not only will it run cooler, it will also clean up your shifts and deliver more horsepower to the wheels (that's why it runs cooler -- less horsepower wasted in heat), which the trans cooler won't do.

When we were pulling 20-foot and 35-foot travel trailers, they required more serious consideration.  The 20-footer wasn't bad -- that's the one that went to Alaska and back -- but for that 35-footer, a trans cooler, engine oil cooler, and HD radiator were all factory-ordered on the tow vehicle.

[bd]

Thanks again for the replies.  I will probably invest in the additional trans. cooler and mount it with a custom frame right in front of the radiator where the old A/C coil was.  I will also consider the synthetic ATF.  I am assuming you shouldn't mix new synthetic ATF with old fluid, so that means I need to drain the converter, too.

I am not pulling anything large, just a 16 foot flat trailer with a small farm tractor and implements.

Traditional and synthetic fluids are miscible, unless otherwise excluded by the manufacturer.  But, (there's always a "But,") you will lose the advantage that synthetic offers to the extent that it is diluted with non-synthetic fluid.

Your proposition of substituting the unused A/C condenser to cool ATF is interesting.  Do some research on the flow characteristics (restriction) and heat rejection specifications of liquid-specific (ATF) versus gas/liquid-specific (Refrigerant) coolers -OR- just try it and see what happens.  For greatest transmission life, keep it cool but not cold.  Run the fluid through the factory wet cooler before the condenser.  This should help preheat the transmission and improve ductility of the metal components, while taking the edge off hot fluid before final cooling, providing tighter temperature control.  Since this is experimental, install a temp gauge using two senders, one on either side of the cooler with a toggle, so you can quantify the temperature drop, then post up the results.  You may start a new trend. 

[mcintyrederek]

That was my thought exactly.  I had even gone through the crazy thought process of bypassing the external cooler when it's not in use with a set of brass ball valves under the hood.  Turn it one way to use just the wet cooler, turn the other way to use both.  That way when I've driving in 20 degree weather, I don't have cold tranny fluid.

On Ebay there are several made in HongKong digital thermometers that use type K thermocouples and come in a very wide range.  Neatly done with a combination of brass flare, tee, and compression adapters, one could very easily install a temp sender on the inlet and outlet coolant pipes near the radiator.  Like you said, this way we could see the temp drop.

I saw bunch of these digital thermometers with remote shielded thermocouples on Ebay for $15.  Not bad.

The condenser coil for the old A/C looks to be 3/8" aluminum.  I don't think there's any restrictions past the expansion valve which will be cut out.  The aluminum piping looks hard and not easy to bend, so flaring it won't be an option.  If it's 3/8" OD, then standard compression ring fittings could be used.  It looks like most of these external tranny coolers are using regular black fuel hose to me, so I'm guessing there's not much pressure on that line anyway, being it's just being pumped and returned..

I'll check on doing this sometime within the next month.  Whether I'm successful or fail, I'll shoot another message and let you guys know how it works.