What is normal operating temp for my 6.5?

[Ben10]

Hi, I am new to the site, and recently purchased a 99 GMC Suburban 6.5, which I love. I have a few questions if someone could tolerate my ignorance for a minute. My truck runs at about 160-165 degrees, outside temp has ranged from 35-65 degrees. Is this the normal operating temp? (I am used to gas engines and about 210 degrees). Next, is there a valve I can purge water from the fuel? I saw this on a Cummins and wondered if the 6.5 has something similar, as I know water is very bad for a diesel. Third, I have about 200k on the truck, and considering Mobil 1 sythetic after reading this site. Is it ok to use synthetic at this point? I do not know what the previous owner had used. I intend to keep this for a long time. Thanks in advance to anyone that helps this diesel rookie.

[chickenhunterbob]

Normal temp should be around 195, or so, depending on the thermostats that are installed. My single set up oem is 195, I think the dual t-stats on the later models are too, not entirely sure though.

If you are seeing lower temps, it may not necessarily be the thermostat(s) that are at fault though, you could verify the coolant temp after the engine warms up if you had access to a tech 2 type scanner, or a infrared type thermometer pointed on the engine side of the thermostats.

The gauge on the dash are not always accurate, if the actual coolant temp is considerably different than the gauge reads, as often as not, the cause is the sending unit up near the front in the driver side cylinder head.

Or it could be the thermostats are not closing, but verifying the actual coolant temp (rather than what the gauge reflects) will verify.

There is a small brass "T" valve near the thermostat housing at the front / top of the engine on the coolant crossover. This is connected to the fuel filter housing by a rubber hose, and is to drain water form the fuel filter. It should have a hose hanging down along the water pump not connected to anything at the other end, put this hose into a container of some sort before opening the valve, to avoid the mess.

Oil? I don't know, I just use Rotella 15w40 dino, but with oil you are liable to get as many opinions as there are types and brands of oil. Synthetic is no doubt better, but considerably more expensive, and the 6.5 will dirty your oil in one trip around the block, so I like to change every 2500 miles.

[DaveBr]

Welcome to the site Ben10

You should have no problem running synth. in your truck. I have 200,000 mi. on my rig and run 5W40 synth in the winter and 15W40 reg. (Shell Rotella) the rest of the year. In the 3 yrs I've owned my truck I've noticed that the oil consumption rate has improved. Why?... I don't know. but I like it. Read January's article in the members area it might give you more clarification. Whatever you decide go with a high quality oil.

[Hubert]

The PCM measures engine coolant temperature independant of the dash gauge. I think i remember the dash gauge is in the head the ECM sensor is in the cross over.

Minimum temp for stable operation is 160F per specs and should be reached within 10 minutes of start up or the ECM with set the service engine soon light.

The ECM resets injection time at 170F from cold start advance IIRC.

Some use 180 Deg thermostats (I have dual 180's and run right about that for temp) I think 195 was OEM. Its a trade off for electronics trucks which is better and depends on usage and climate of local. The engine (fuel burn) will run better at 195 but underhood temps will be higher and harder on the electronics. The debate rages as to what is better.

Most quality thermostats will open within 3 degrees below and 4 or 7 above temperature and They open pretty far pretty fast its not linear mostly open or closed but should go fully max open at no more than 15-20 deg above set point.

like Chickenhunterbob says double check accuracy of dash gauge. The odd ball tick marks tends to make me misread the temp reading.

[Ben10]

Thanks for the info. I will pick up an infra red and check the temps to verify actual operating temperature. Another thing I forgot to mention is that the heat is rather weak, another indication it might actually be running in the 160 range. We just took a 4 hour trip, outside temp wasin the low 40's, and we had the heat maxed most of the trip. Usually that will cook us here in Florida. No big deal, in about 4 weeks we won't need heat again until November.

How often should I check for water in the fuel system? Thanks.

[chickenhunterbob]

Thanks for the info. I will pick up an infra red and check the temps to verify actual operating temperature. Another thing I forgot to mention is that the heat is rather weak, another indication it might actually be running in the 160 range. We just took a 4 hour trip, outside temp wasin the low 40's, and we had the heat maxed most of the trip. Usually that will cook us here in Florida. No big deal, in about 4 weeks we won't need heat again until November.

How often should I check for water in the fuel system? Thanks.

The fuel manager (canister at the rear of the engine where the filter is) has a water sensor in it, if there is water in the fuel manager a "water in fuel" warning light will appear on the dash. So there is no need for you to check for water.

Mine has only ever come on once.

It is probably a good idea though, to drain a little out just so you know how. If your water in fuel light comes on some day down the road in the dark of night, you'll know where things are at.

Also, opening the valve will let you know if (or reassure you) the lift pump is working. If the "T" valve is opened with the engine running, it should produce a steady stream of fuel (~ 1/2 pint in 15 seconds, or so), if the lift pump is not working, there will be next to nothing and the engine will die.

[zig9765]

if it does turn out to be your thermostat save your self a headache down the road and get them from the dealer or i have seen good one at kennedy diesel they both flow a lot more coolant than just a regular old thermostat

[Robyn]

Welcome to TDP :D:D:D

I have been running 6.2 and 6.5 stuff since they came out back in 82

Your temp issue may be a stuck T stat. The 99 has two of the little beasts in the oblong stat housing.

As far as oil I have always run either Delo 400 15-40 or Rotella T 15-40

I personally have only used Synth once in a 6.5 and then only because thats what was in it when I bought it.

I run big rigs and have always had good luck with the Rotella T

If your heater wont run you out at 40F then you probably have a stat stuck partially open. 6.5's dont have any issues with making heat. Normal temp is 195F I prefer 180F stats that are open and flowing at 180F

The 6.5 does not really like temps above 220F and with warm weather comes slow city driving with the AC On

The 180F stats will give pelnty of heat to keep things happy as well as allow the heater to work well too even in very cold temps

Best

Robyn