6.5 questions

[dgrund61]

new to owning a 98 1/2 ton 6.5 automatic, and have questions; whats the operating temp for the 6.5? Would a lift pump cause a surging at higher speeds such as above 65? Rpms seem to stay constant, transmission doesn't sound like it's shifting in out of 4th. trying to figure out if it's engine or tranny. Truck has 160,000 on it; new injector pump @ 115,000. Trans fluid is dark but not real burnt smelling. Any help is appreciated.

[6.5guy]

Welcome to the forum

Our 6.5 usually don't reach 210 unless we are pulling something heavy and it is hot out. Even then the guage stays around 210. Does it surge on level ground, going up a grade or just at random?

[damork]

Dark red automatic trans fluid tells me you should flush the transmission. I always add Lube Gard to the trans fluid flushes. Maybe add a temp gauge setup to the pan, add a 25000+ BTU cooler in place of the OEM unit (search for the TruCool brand - it is the same supplier as OEM unit, (I have an LB7 if I recall correctly). Find it at www.bulkpart.com (http://www.bulkpart.com) for a decent price. My transmission has not not failed and am at 258,000 miles - enough said about trans temps & flushes.

Engine temps with 180F dual Robertshaw thermostats should keep you right at 180F, mine runs right at that unless it is real hot and humid, then it might creep up to 185F. Check for bugs and junk in your radiator or between coolers and AC condensor & radiator.

A couple things to check on your transmission shifting into 4th. I had a trans shop tell me my trans was shot 60k ago, then found out on this site that checking trailer wiring harness for grounds and shorts might be in order. Well - the trailer harness was badly corroded at the back bumper. Cleaned it all up, replaced bad wires, fixed the grounds, including those on the frame near the fuel tank, those at the right rear stud on right hand of the engine intake manifold (near firewall). Harness grounds to frame from that stud too. Biggest wiring discovery was the black wire that grounds the blower motor on the passenger side. It is a spot where the ECM (computer) shares ground with the blower. I replaced the motor and found this terrible ground there so added grounds from this location to the dash support bracket. This provided a big improvement to how the truck has ran, even with over 200k miles, in fact it has run better in the last 100k miles than it did before then. Electrics on these vehicles is probably their biggest weakness, and it isn't very hard to fix a lot of it. I learned to leave AC Delco alternators alone when they fail and found Duralast Gold from Autozone to be a huge step in the right direction - they actually hold decent voltage at stop signs with lights and AC or heater on.

A pre-lift pump fuel filter or water trap will help eliminate problems down the road - Stanadyne or Racor have units with 30 micron elements that do the job.

Check the speed sensors on the transfer case and automatic for debris - they are simple to unscrew and have magnetic tips. The tips should be clean of debris and will not allow the automatic to shift right if dirty. I found many transmission shops did not know how this impacts performance, but a Hummer bulletin mentioned it a while back and it solved a shift problem I was having. I also added 12v hot relay power to feed the automatic transmission to reduce the load going across the ignition switch. A lot of power goes across the ignition switch to power different things that should really be fed by relays. I bought Bosch 12 30Amp relays to do the job.

Hope this helps.

[dgrund61]

I checked all the grounds you mentioned, nothing stood out as being in bad shape. The surging is more random than anything. I think it happens more when it is coasting , like it can't decide if it the converter wants to stay locked up or not. However i noticed tonight that my voltage has dropped from normal14.5 down to 13.6( I checked it with a meter on the alternator); Makes Me wonder if the alternator is causing the surge, but the rpms and speedometer never change. Will check this out. Other than a few minor issues, so far I am happy with this truck.

[dgrund61]

checked alt. passed all it's tests, checked egr valve seems to be working. I figured out that it's an engine problem. With the truck in park, you can run the engine up to 1800 before it sound like it's missing. It will do this up to about 2300. Changed fuel filter, and burped it; checked lift pump; seems to be working. Looked for vacuum leaks; couldn't find any . Is this sign of a dying pmd, or is there something else i should look. Any help appreciated