Hot day - engine temp climbs

[jerry598]

I've got the 97 cooling mods installed and today with temps in the low 90's was the first time I've really driven the rig in any kind of heat. The temp guage readings have previously been just above the 1/4 mark, or supposedly around 185 even with 195 degree t stats installed. Put my foot into it on a 4 mile stretch of flat highway pulling a very light trailer (about 1,500 lbs) and brought it up to 65 mph. The guage climbed to just shy of 210 at the 1/2 mark and held steady. Upon slowing down she cooled right back down to the 185 area without any problem. Question is: Does that sound normal?

Also, I've got a new fan clutch and 9 blade fan (don't remember who I bought it from but it was not Kennedy or Heath). It's supposed to kick in at 185 degrees but I never can hear it. Should I be able to hear that 9 blade fan kick in when the clutch engages?

[DmaxMaverick]

Your experience sounds mostly normal. Mostly meaning, you are on the cool side of the envelope under minimal loading. Running too cool robs you of some power and economy. Ideally, the engine operating temp should be as high as can be managed (within reason, of course).

Being able to hold steady at or below 210° is a "normal" indicator. Don't take the gage reading too seriously. OEM dash gages are better tools for tracking trends, than actual values. Add to that, the function of the entire system, and the indicated values become more and more useless.

You should hear the fan when the clutch engages. It sounds to me like it didn't engage, and probably shouldn't have, as it was not needed (indicated by the temp holding below 210°). The thermostat rated temp is somewhat vague, as well. Some are more accurate than others, and different mfg's employ different ranges of operation for specific ratings. Most begin opening at about 5% below the rating, are at about 50% flow at the rating, and are fully open at about 5-10% above the rating. With this in mind, it is likely the coolant wasn't at the required temp to engage the clutch by the time the air was passing through the radiator to the clutch (the ONLY thing that will cause the clutch to engage). This is a very normal condition, and indicates a healthy cooling system under the circumstances. You'll have to push it harder to find your limit.

[Robyn]

I might add a couple things.

What Maverick mentioned about the gauges reliability as far as accuracy is spot on.

Now here is a real test of ther system. If you can maintain a good steep grade at 65 MPH with your boot on the skinny pedal and not see the temps climb above the 210 mark, the system is probably doing ok.

The Radiators in these things are MARGINAL when new. After 10 to 15 years of pounding down the Boulevard the radiator cores start to "silt in" and the lower tubes start to or do plug up with crud.

The core size on these trucks is about as big as the chassis will accomodate but is still a tad small for the amount of thermal disipation required under worst case scenarios.

As we add HP goodies and ask the little 6.5 beastie to do more than Ma General had envisioned the radiator reaches capacity.

Its amazing what a fresh radiator will do to help curb the heat issue.

When I rebuilt the DaHoooley last summer, I replaced the radiator with a new OEM quality "Visteon" unit. (aluminum brazed core and not epoxy)

The engine temps will climb to 205 under a hard pull (I have a direct burbon tube gauge installed at the LH head sender location) The 205 number is likley close with the quality of gauge that I installed. I have a 180F stat with the standard OEM type pump and single stat crossover.

Once the temp settles at 205 it then plunges to 180F or there abouts again and the cycle starts over.

I agree that the cooler stat probably robs a tad bit of power ???? but I prefer to keep the temps a bit lower as the thermal stresses on the engine are lower too.

If you find that in hot weather and under a hard pull that the temps will not stay below the 210F mark and if the rig is pushed, that the temp climbs even a tad more, its an indicator that the radiator is not up to par.

With a radiator thats loosing its ability to reject heat, the fan clutch will also fail to do its part too. This is due to the lack of heat being released in front of the fan clutch Bimetal spring that controls the clutch valve.

Good luck and keep us posted on how things go.

Missy

[jerry598]

Thanks for the replies! Guess I need to test her with a load on a grade. Will let you know how she goes!

[Stratosurfer]

The Radiators in these things are MARGINAL when new. After 10 to 15 years of pounding down the Boulevard the radiator cores start to "silt in" and the lower tubes start to or do plug up with crud.

Missy,
Are we to never 'flush' our radiators anymore? I don't hear of folks doing it, the coolant is so much better and all. As a young whipper snapper I used to annually back flush my rads with the old Prestone kit.
Can this be done to get some crud out?