95 GMC 1500 Heating Problems

[Dibsing]

Hey, My brother has a 1995 GMC 1500 with a 4.3 V6 and he recently got 2000$ of work done to it where almost 1/2 of it was done to the cooling system

NEW:

Raditator flush
Heater Core
Hoses
Heater hose coupler
Thermostat (tested and worked fine)
New coolant

The truck blows warm air when the engine starts and as the truck runs it seems that it starts to blow less and less warm air as the truck warms up. The temperature gauge fluxuates like crazy between 70-100oC. It drops drastically and slowly comes back up to around a 100ish.

Before all of this work was done the truck didnt do anything like the above execpt for leaking coolant from the coupler.

Could this be from a bad water pump or anything else im running out of ideas and dont want to pay another 2000$ in repairs to the truck again to find out the problem.

Thanks

[fuzzypuppy]

Wow a grand for what basicly amounts to a heater core and a couple of hoses and they didn't even throw in a new thermostat, sounds like a rip to me.
Anyways, sounds like there is air trapped in in your cooling system if there is air and not warm coolant passing through your heater core and around your temp sensor both will act as you have described "irratic".
Since they vacumed your pockets so throughly before and performed what amounts to shoddy work by not bleeding the cooling system they just serviced I hate to say take it back to the shop that performed the service, but they do have a responsability to correct the problem.
I would not let them sell one more service, or shell out one more cent though.
good luck.

[Dibsing]

I managed to get some time away from my Finals and found out that its the heater controls inside the cab wherent being turned all of the way, so now we got hot air comming but the truck still seems to loose temperature

First starting the temp rises, and when it gets to around 100 the gauge goes all the way back to 70 and slowy creeps back up again to around 100 and then back down to 70. This just keeps on going on, it sounds like the thermostat is not opening and then all of a sudden it opens and cools the engien down and then closes.

Hopfully this helps

PS the heater core was done by myself and my brother the garage didnt do that