High/Low temps in mountians?

DEK · **Joined:** Sat Sep 03, 2011 12:52 pm **Posts:** 5

Drove my 05 CRD in the Smokies for the first time this week. Suspected even before the trip that I may have the oem weak fan clutch, so I wasn't surprised that the temp guage got up to two marks from "H" before I reached the top of Balsaam Mtn (5,400 ft). But what surprised me was going down the temp guage dropped to the 1/4 mark halfway down. Also, the AC was not very cold going down as opposed to the climb. Wasn't towing anything by the way. Any thoughts on why the temp dived, and AC underperformed? (No CEL, ran fine, got 32.5 overall mpg on trip from Columbia, SC.)

papaindigo · **Posted:** Sat May 05, 2012 12:08 pm

What was the ambient temperature and can I assume you were running the AC both ways? If the temp was in the 80s F or higher and you were running the AC my guess is your tstat is on the way out (how old is it?) and the ambient temp with AC use is masking that fact until you took the load off the engine going downhill. I know when my tstat was dieing that on colder days (60s or below) with no AC it ran at about 3/8ths on the gauge but as soon as things warmed up and I started to us the AC the temp gauge needle ran only a hair left of vertical.

On the downhill run were you coasting at low rpms? If so AC won't cool as well at low rpms as it does at higher as the AC compressor is driven off the serp belt so it runs in time with engine rpm. The FSM has a pretty easy AC performance check using a thermometer. See 2005 FSM pages 24-4 & 5 for test method. Do test after car FULLY cooled which takes about 10 miles on a really hot day at max. AC. June 2010 readings on my 2005 were 45 and 48 at 75 and 95 ambient respectively.

The FSM has a relatively simply mechanical fan clutch test also.

DEK · **Joined:** Sat Sep 03, 2011 12:52 pm **Posts:** 5

Air temps were in the low 80's as I recall. I assume that the tstat is origonal, as I just bought the crd last year from a dealer. Don't know much about the prior mech. history, other then it only had one prior owner. Normally I pull a 3000 lb trailer on a mix of flat/ rolling hilly terrain mostly highway with no abnormal cooling issues. Have had a few instances of it running a bit hot on some 85+ degree days when I got stuck in stop and go traffic. Figure I will be putting a new Hayden fan clutch in the next few days. Downhill the rpms were low- around 1200, didn't down shift at all. I didn't know if the long downhill grades and not shifting to a lower gear (just using brakes), may have somehow caused the engine to overcool. I get what you are saying with the low AC/ low compressor rpm performance. Makes sense. Not sure about the tstat though, any thoughts on how to test it? Thanks for the input.

MrMopar64 · **Posted:** Sat May 05, 2012 1:23 pm

With warm ambient conditions it should never drop below the normal thermostat start-of-opening point.
In cold ambient temps it can run 5-7degC below the T-stat set temp due to the cold air cooling the surfaces of the block.

If it's an original T-stat, it more than likely doesn't work anymore.

DOC4444 · **Posted:** Sun May 06, 2012 10:24 am

Consider the inhose thermostat mod. It is quick, easy and works well.

DOC

TJ2 · **Posted:** Sun May 06, 2012 2:03 pm

DOC4444 wrote:

Consider the inhose thermostat mod. It is quick, easy and works well.

DOC

+1 Also, the Hayden 2905 fan clutch is the recommended replacement. I got mine overnight from O'reilly for about $55.

The T-stat and fan clutch were not working when I bought the vehicle. The PO was running cold in winter and hot in summer.

DOC4444 · **Posted:** Sun May 06, 2012 3:27 pm

Pull the viscous heater relay to add 3 mpg until you get a GDE ECU.

DOC

TennesseeCRD · **Joined:** Mon Jan 11, 2010 11:01 am **Posts:** 181

I live near the smokies and have pulled that same mtn with my crd. I did the inline hose thermostat last year and it worked flawless pulling the grades as well as going down. It never moved past the half way point going up and never below a mark below half on the way down. As for the ac not cooling, mine seems to cool as well at idle as it does at speed. Have you given it a 134a boost lately? It may need a little charge.

retmil46 · **Posted:** Mon May 07, 2012 2:05 pm

Thermostat is dead - no question about it - mine did the same prior to replacement.

You need a new thermostat, hayden fan clutch, 11 bladed nylon V6 mechanical fan.

Also, an aux tranny oil cooler will help remove some of the heat load from the factory combination tranny oil cooler/AC condenser and improve A/C performance. Agree with the assessment that this being a used vehicle, need to get the freon charge checked for proper level as well.

All above mods on mine, had no trouble contending with 100 plus temps in southern TX and providing cold A/C.

Unles the clutch is gomered up, no need to unplug the aux heater pump once all the above is working properly.

High/Low temps in mountians?

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