I have a overheating problem that happens randomly. Every now and then my temp will rise, it would go into the red if I let it. While driving it will stay at 9 or 10 o'clock position and head toward red line while still. If I put it in neutral and rev the engine to about 1700-2000 rpm while at a stop light let's say, the temp will not red line, will stay at 9 or 10 o'clock. My normal running temp is 8 o'clock position. This dose not always happen, this happens maybe once every other day and only for one travel stretch. Im thinking the thermostat is sticking every once in a while, having gotten ahold of one yet to change it. Any one had this problem? Suggestions?

 

I would suggest getting a gauge to tell you actual temps.If you go by the rover gauge you will toast your engine.It will not show overheating until it is too late.There are tons of great post and info in the D1 section.

 

I haven't found a post with random overheats like I'm experiencing, all seem to have consistent overheating parameters

 

I take it that your D1 runs a normal temp, but when going from highway to idle or slow it has a temperature increase. I'll take that to be bad viscous clutch, clogged radiator, and maybe thermostat. Likely all three. With a partial clog radiator you run good temps as long as you are at good speed, then heat up quickly if low air flow. A bad fan clutch makes such low air flow.


On a D1 your investment in a new stat is like $10, gasket, turn two bolts, and a half gallon of coolant. I respectfully suggest a 180F stat, not fail safe type. The spring end goes inside the block (for other noobies) and the little hole or jiggle device goes at the 12:00 position to allow any steam to pass and not form a pocket.

You should also check you viscous fan clutch. At low speed or idle it provides the cooling, which by your description is not happening. When truck is cold, NOT RUNNING, flip the fan blade and see how far it coasts. Should be less than a full revoultion, should feel like peanut butter in there. Then warm up truck, turn off, and repeat. If it freewheels more than one turn, then the fluid inside has been lost. It just isn't moving much air at idle. DO NOT try to hold fan with stick, gloved hand, bannana, or any such shop fable.

The fan clutch is abut $60, same as Chevy 2000 Express van, 4.3 liter, w/o AC. Their AC version is too large. When truck cranks up cold should make a roar, as fan is fully coupled. On my 97 the blades of the electric fans spin slowly due to that air flow. In a very short time the fluid circulates and the fan power coupling drops to 20% or so, can still take off part of a finger. Roar drops away.

If fan makes roar at idle, and passes the spin test, it may not be getting hot enough to re-couple. The faceplate of the fan warms up and makes the fan re-engage at higher coupling power. If the radiator is blocked with mud and leaves there may not be enough air flow at the middle, or if the radiator is clogged inside with crud and calcium the same thing can happen. You can verify the radiator by measuring temp on the fins top to bottom in a vertical line. If more than 10F cooler on bottom rows, they are partially blocked. You won't be able to cure by DIY flush, but a rad shop can unsolder a side tank and rod out the calcium build up in your $600 radiator. An aluminum after market is like $235. Radiator rod out near me at small indy shop was $75, carry in.

On an older truck it is not uncommon to have multiple problems. If you have a scanner or Ultra Gauge you can see the temperature in digital form. Anything above 50% is already overheating.

A cracked block or head gasket can also do this, usually has extreme boil in coolant jug, loss of coolant, sounds like bubbles rushing inside pipes under dash.

 

Replace the t-stat, then the fan clutch, this sounds like a water pump going bad.
The impeller is pressed onto the shaft and when it starts to slip it only pushes enough coolant at a higher engine speed to cool the engine.

 

Yep, with those miles the WP is at end of service life. Will begin to wobble the pulley, leak out the nose, etc. It is supposed to push 2.64 gallons at 10PSI at 1000 rpm. Don't know if you would see the swirl in the coolant tank from circulation thru the throttle body heater drop off, etc. I suspect that some old pumps have enough scale buildup that they don't slip. Some after market pumps have the bronze impeller to avoid this problem in the future.

An important point, if clutch or WP is changed at this point, the other will likely fail soon after. Both have been bonded together and danced around the floor for millions of spins, and have grown used to each other's warts. The will be micro imbalances with just one new part, and the old one doesn't like it. If you can, change both. Or budget for second one.

It is quite easy on the cooling system to have multiple problems, which add to the overall issue.

 

Thanks for all the info! Fan spin test passed. I'm going to replace the thermostat first and go from there. Hasn't overheated in 3 days. Trips ranging from highway to back roads, stop and go to highway, no highway, only slow go and nothing, let it sit and run for an hour and no issues. Going to get a thermostat on order, local only has 195 degree. Will order 180

 

Gosh, most stores carry a 180, the same stat fits like 3000 different models, GM, Ford, etc., etc.

Also, if overheat comes on quickly at idle, might try finding a long hill, shift to N, coast. If you are at 15 mph or better the air flow from forward motion exceeds the fan cluch. So if it stayed cool, the WP may be in the clear. Also, I would think that the WP and clutch would show up almost every time, not every three days or so.

 

I run a 195 t-stat, have since I bought the truck in '07.

 

Alright here's an update. I got a new sender unit from my local shop, Nigel's car place, and that fixed my gauge problem right off the bat.but then I started to have legitimate overheating issues, I even drove almost 80 miles at redline and my engine is still working,I am very fortunate not to have had any issues with that other than boiling over a ton of coolant.so to address my now over heating issues I removed my thermostat took it inside and boiled it in a pot on the stove, the thermostat did not open even after boiling for at least 10 minutes, so I will ordered a 180 thermostat. install the new thermostat today drove around for awhile and everything seems to be peachy. Tomorrow I will take it on my profile on highway run and see if my temps stay normal to solidify that my problem is solved. Thanks to everybody who responded the pictures that were posted helped me a whole lot in finding out where everything was. thanks a million