It's time to play waterpump OR head gasket/cracked heads, with your host, 2000 Chevy 6.5L Diesel!

Back story: I've been ignoring an issue on this low-use truck for about a year, and finally got off my arse to look at it (read: pay someone else to deal with it). My hypothesis was the water pump is dying.

Symptoms: During plowing in the winter time, I'll only ever get slightly warm air out of the heater (~55° when it's ~15° out, not enough to keep the cabin hot). If I drive around @ > 50 MPH with the plow on, the temp gauge will overheat unless I get the plow in the exactly perfect position, but the heater air will still be cold. In the summer time, when it's hot out, if I'm towing a trailer (say a u-haul with a Miata on it), the temp gauge will go up if I'm putting any real load on it going up a hill. In either case, if I let off the load, by the time I idle down the other side of the hill I'm right back into the happy temp range (~190-220ish).

It doesn't seem to use or add anything to the cooling system, the hoses feel (to me) like they're pressurizing normally and there's no sign of contamination in the oil.

Troubleshooting thus far: I took it to the mechanic who used to be a chevy tech before opening his own shop. He's admittedly "not a diesel guy" although he says he worked on plenty of these when he was at the dealership. He feels that due to my description, it's probably a head gasket allowing pressure into the coolant or a crack in the heads. "These 6.5s are just as likely to crack a head as lose a gasket," he claims. With that thought in mind, he did a coolant hydrocarbon test which came back negative, as well as a coolant system pressure check which also came back with no problems.

His hypothesis is that a crack in the head is causing the coolant to pressurize a bit, which is resulting in air in the system that then bleeds out the pressure cap. This part doesn't really make sense to me?

He doesn't want to dig into the waterpump project because it will be costly, and he feels that it's not going to solve the problem with I really, really appreciate. He also says he's not comfortable tearing down a 6.5, and doesn't really have time to tackle a project like that which I can also appreciate.

What do you guys think the next step is? I really didn't want to replace the water pump myself because dealing with trucks is a PITA :) Should I seek out a diesel specialist? Should I pull the heads and have 'em checked?

Thanks!

Sounds like a WP and/or thermostat problem. At this point it doesn't make sense to pull the heads.

Thoes are easy to replace WP and tstat. id say start there

I would pull the water pump and check for a bad impeller. These are dual thermostat trucks so remember to replace both as a pair.

I am a pro when it comes to the 6.5s, generally the head gaskets or heads fail pretty spectacularly, external leaks or heavy consumption are pretty good signs something is amiss.

As far as tearing into it, don't be skeered. Water pumps on these are just like any other V8, there is a ton of room under the hood. If the truck is not a total rusted POS you can pull the inner fenders out in about 5 minutes and that gives a lot more room to work. Also, you will need either a water pump tool, or a huge channel lock and crescent wrench to break the fan free, or you can do the hillfolk trick of bumping the water pump nut with an air chisel to get it spinning. Its normal (RH) thread so no surprises there.

Always start with the simplest thing first, I think your thermostat is just stuck halfway open.

As others said it sounds like a WP to me. I replaced mine about a year ago, to be honest, it's a PITA in this truck. You have to basically remove every accessory on the fornt of the engine when you do this, so if you have the time and money just go ahead and replace all the tensioner pulleys while you're in there. Also be sure to get the HO (high output) unit.

There's plenty of room to work in there, it's just a time consuming process.

Could be the sending unit for the gauge. Put a heat gun on it.

What about a radiator ?

Glad to hear that you guys agree that it doesn't sound like a head gasket/cracked head.. the description didn't fit within my understanding of thermodynonsense.

I guess I'll try to tackle it myself then, thanks for confirming that it's a PITA, torx.

95GSX- luckily I already made a tool to remove the fan, so I'm good on that front. Thanks for confirming that it's a doable job :)

Dean & beatmtn - I don't believe it's the radiator or the sending unit because of lack of heat.

Oh and the damper pulley, replace that too. The rubber dries up and it'll break the crank in two when the damper comes apart.

I have once seen a head gasket leak where it didn't get coolant in the oil, didn't use any coolant but pushed air into the coolant. The coolant got cloudy and funny smelling after a while. And you could hear the air bubble it would form in the heater core.

But I agree, sort out the simple stuff first as that's all more likely than a head gasket issue.

Did it have symptoms like this, rslifkin?

WonkoTheSane wrote: Did it have symptoms like this, rslifkin?

No, it didn't. Strangely, the air bubble in the heater core after running it hard was the only symptom until I noticed the coolant starting to get cloudy / smelly. It never put enough air into the system (compared to what it could push out to the overflow tank on each heat cycle) to run hot or anything. It was spring, so I can't say if the heat may have been a little weaker than normal, but it still worked.

Hmm... My coolant seemed fine last time I checked, but since it's always nicely between min/max on the cloudy overflow tank, I'm not 100% sure. I'll check.

If the coolant is clear, I'll take it as a sign that once again I can't pay someone else to solve my problems and do the water pump...