02 lb7 Heats up then cools down

[9365turbo]

So what would cause my truck to heat up to 180 then cool down to 160 or less aka freezing. Then not long later it heats back up and stays there 180. I'm driving in town. takes about 5 miles to warm up. I suspect the head gasket. I do have the grill cover on,not the bumper cover. Thanks

[DmaxMaverick]

Sounds like sticky thermostat(s). Unless you've lost a significant amount of coolant lately, don't be so quick to blame a head gasket. It could also be some air in the cooling system, for whatever reason. Has the system been open or serviced, lately? It could be as simple as needing a service.

[Mark Rinker]

...or a new overflow bottle cap.

[9365turbo]

I have had problems with coolant blow outs but not in a while. (It only seems to happen when I run it hard or towing) The grill cover has been on even when its above freezing.It might have some air it there. What do you mean by servicing? I havent had alot time to work on it. Been working on other rigs.

[Mark Rinker]

Replace the thermostats and overflow cap, first. Bleed the entire system of trapped air bubbles. See what happens, next...

I would not run the grill cover, unless its below 10F. Even then, not when towing. Its been below zero here, mine isn't on yet and still makes good heat. Mostly I run it in front of the snowplow to keep sand and grit out when plowing snow...

[9365turbo]

I give that a try. Thanks

[Kennedy]

I think you are fooling yourself into thinking it's something simple. Having had coolant blowouts says it all. You have a head gasket leak. It puts air in the system. This air builds behind the stats and makes for the temp swings you described.

Bleeding the system is not necessary except on initial fill. If there is air in there and teh bottle is full it will purge itself after a short drive. Because it repeats, you are making "air" in the system.

[JohnC]

This is the same behavior I was having, except I never had a blow out. Basically, if you're getting bubbles into the tank, they're coming from somewhere, and the possibilities are very limited. If the system is still pressurized after it cools down, that's another dead giveaway...

[9365turbo]

Why dont I get any white smoke if I'm burning coolant? It only blows out when you tow or run it hard. Normal every day driving its fine. I dont dought it can be the head gaskets,but could it also be the injecter seals? The injecters were changed before 100000. It now has 180000. I had to replace the water pump right after I bought it last year. What will need to replace the head gaskets and injecter seals. Other then lots of money?

[JohnC]

Why dont I get any white smoke if I'm burning coolant?

You're probably not burning coolant. It's a lot easier for combustion pressures to leak into the cooling system than the other way around.

[9365turbo]

Well I went out and opened the bleed screw. Air did come out. As it was warming up to purge the coolant bubbles were coming out of one of the hoses on the coolant tank. I guess I should stop being in denial and replace the head gasket and the injecter seals. I know this has been asked before,but what special tools do I need and whos a good source for parts.

[TomJ01]

I have a 2001 D-Max. I had severe temperature swings and coolant pukeing from the botlle overflow. The temp. would start to climb, toward normal, and suddenly start downward. At times I would see it go from 140 to 70 degrees. I followed it digitally on my Banks Stinger PDA. The stock analog gauge will show it but not well. My truck has never been diven hard!
I followed the GM shop's recommendations and spent lot of cash on injector sleeves, thermostats, etc. The problem was head gaskets. It was a problem that gave me fits, intermittantly for over 2 years. All coolant analysis tests by GM and independent shop showed no exhaust gasses in DexCool, even with system pressurized.
Get someone good to do the job unless you can do it yourself. I had coolant leaks, a bad water pump, bent pulleys, bad seals, etc. after spending about $7,000. Much of the work was later redone by another shop. GOOD LUCK, I know how truely painful this can be.

[9365turbo]

That sounds exactly what mine does,but it happens intermittantly also. I'm hoping it will stay together until spring. Then I plan on fixing it myself. I dont drive the truck everyday so it should. I will have to find that injecter pulling tool when I'm ready to get it done.