Headgasket Thoughts

[xohcef]

So I'm used to my Honda overheating and changing a headgasket. Well I'm weary about my truck and how it warms up and keeps temp in cruising speeds even without any load. I do let it run at least 10 minutes to get some heat in er on cold starts but was told it had an auto parts thermostat on it and not an oe cummins part number. The temp gets up over the 2/3rds til the thermostat cycles for the first time after cold start. After that the temp even sees just under 2/3rds at 70mph without any load. I'm trying to see if this is normal or if I need a cummins part number thermostat. I plan on towing with the truck and over some big hills too. Temps gotta stay normal if it isn't. Thanks in advance

[ellis93]

I've not had any luck with part store thermos. Some made it hot,some made the temp gauge try to hypnotize you with the needles swing.
I bought one from cummins and I've not had any problems since.

[Mark Nixon]

I have a 1991.5 that always seems to run "at least" half the gauge all the time, after initial warmup.
Coincidentally, I've changed radiator and fan (a clutch imploded), replaced the complete gauge package, replaced the hacked and burned engine compartment harness, which had ZERO effect on it running warm.

There's been times when connectivity issues, like bad wiring or gauge boards caused me erratic gauges, but this isn't WHY I replaced any of it, but I figure if it was part of the PROBLEM some difference would have been noted and none was.

I just live with the fact that it runs "a little warm" and it's never overheated on me, even when I pulled my old 2-car with it.

Mark.

[welderboy250]

As odd as it may seem I've had a clogged heater core cause weird swings on the gauge. On my truck it was acting strange and i kept having less and less heat so I clamped off the heater hoses, pulled them from the heater core, flushed it both directions multiple times. Got a bunch of crap out of it. Hooked back up and topped of the little bit of coolant I lost, and it was all good, including the gauge swing practically disappeared.

[bwgarrett56]

I've not had any luck with part store thermos. Some made it hot,some made the temp gauge try to hypnotize you with the needles swing.
I bought one from cummins and I've not had any problems since.

I had the same thing happen. Put in a cheap one and the temp went to the 3/4 side of the gauge. After my rebuild project I put in a cummins and it works much better. Make sure that you get all of the air purged out of the cooling system. That seems to make things more consistant.

[TRACTJDS0428]

I have exactly the same problem with my 93 w250. swings up almost to the hot mark the first cycle and drops all the way back to the cold mark then only floats about half the guage after the first cycle. Its had two Stant thermostats and a new water pump, fan clutch, radiator, temp. sensor, and belt and tensoiner. So a Cummins thermostat should fix it? Its consistant so i dont think its a wiring problem

[Tacoclaw]

If it's the first spike before the thermostat dumps that is worrying you, then yes a Cummins piece should fix it. If its maintaining temp while at no-load cruise, then no nothing will change. I put a new Cummins piece in my truck and it will go right up to the first thin line and stop there.

The only time it changes is if I let it idle with the fan on, it will slowly drop to the first fat line, or if I'm really running the crap out of it, it will just edge past the first thin line. I've never had it get higher once the fan was operational.

At an idle with no fans and not moving, I've had it get to almost 3/4 of the gauge.

[BILTIT]

I installed a new cummins stat and it does the same thing. Gets up to about 2/3rds or so then drops of to 1/4ish. My old Non-cumins stat was better.

[quickie70]

stick a mechanical gauge on it before you tear into a head gasket. I've decided all of the senders on our engines rattle themselves silly and read wacky. My truck will turn the oil PSI idiot light on, and bury the gauge to nothin getting off of the highway after a long run, and my mechanical gauge reads 30 psi. That said, my mechanical temp gauge reads 200* when the unknown brand/temp thermostat will open (sending unit is right next to the thermostat), and my dash gauge reads about 3/4. After a few minutes it'll settle into about 175-185* (depending on load, temp outside, etc, obviously), but the dash gauge reads about 3/8 up the gauge. If I've got it loaded up and headed uphill, it does the same. 200* is 3/4 on the dash, at least in my truck, but there's no way Dodge intended only a 15-25* swing through the middle of the gauge.

[welderboy250]

2x on verifying the stock gauge reading and by all means make sure the heater core isn't clogged. I know it may sound crazy but I swear I've seen it do weird things.

[xohcef]

Good ideas guys, thank you. I do have a mechanical oil pressure gauge to validate the cluster might have too do that as well with the water. How involved is a heater core job in one of these? I couldn't imagine it being too bad.

[PToombs]

You don't have enough imagination.

[cmann250]

Mark explained a much simpler way that involved some rotating and twisting to me. Fortunately I haven't had a chance to try it yet

[Tacoclaw]

Couldn't you just unhook the hoses and run water through it while it's in the truck? Or water and whatever you use to clean them out.

[Mark Nixon]

Yeah, that's called "flushing".
Reverse the flow and its "backflushing"
I wouldn't try to clean the heater core with cleaners, as that's had remarkably BAD results for me in the past.

One thing you could do to eliminate the heater core as a potential suspect would be to take it out of the equation, by running a hose between the inlet/outlets to it, "bypass" it, I guess.

I'll say one thing about the "mood swings" of the temp needle, if you're working a truck that does this, it does NOT seem to do it under heavy towing conditions.

As far as the needle's actual tendency to move, I'm convinced that having the sending unit clear on the other end of the head from the thermostat, also plays a role in these swings.
Put the sender up by the t-stat and you'll likely have a more consistent and accurate reading.

Mark.