New member and first post. I picked up a 2008 Sierra 1500 with a 4.8L and 243 heads, The engine keeps blowing the back off the water pump. 3 different pumps. Cleaned radiator, changed all hoses and new thermostat. Same results. No idea why 243 heads are on a 4.8L. Kinda at wits end. Does anyone have any ideas?

 

Did you test the expansion tank cap?

 

I didn't actually test it but the tank does overflow but pressure buildup still blows water pump back cover.

 

Are you purging the air out of the system effectively? Even a kittle bit can cause quite a problem. JMTC

 

I am attempting to. Can't guarantee it.

 

All the gen iv 4.8s and 5.3s have 799 or 243 heads... it's not an irregularity. I have seen more 07 through 09a with 243s on them than 799s for that matter.

Well it seems odd to me anyway that a hose could withstand pressure more than the rear cover of the pump.. but it's possible. My 05 is on its 11th water pump since new... it literally took 10 pumps to get a decent one that works and doesn't have some bullshit problem. Even the dealer high priced oem ones always either leaked or did something wrong. That said the GM one on it now has survived for at least 25000 miles so that's a plus!

I would maybe switch brands or even get a used one and run with it. If it's not overheating and not running excessive pressure which you should check its probably just junk pumps. A pressure test though would be the first on the list to see if you are over pressuring the system..

 

It is overheating and losing coolant. I will check system pressure first chance I get. All the pumps have been Advance Auto Reman's. Any recommendations for sourcing a good pump.Going in hospital 5:30am for heart procedure called Ablation. Something to do with stopping AFIB. Will let you know as soon as I can get back to it. The "deal too good to be true" is turning out to be just that on this truck.

Thanks/Dave

 

Son just reminded me we did pressure test on system. Everything was in spec. Between us we have had 8 gm trucks. 2- 5.7L, 1-8.1L, 3 6.0's and new 5.3L and a 454. This 4.8L is first for size and first we have had waterpump issue on and we have put lots of miles on all trucks. We both have worked mining and construction so are on the road a lot.

 

I don't know what the problem is, but I think everything is surviving because it's a surface area/physics thing. That rear cover has a ton of surface area compared to the lower hose, for example.

Dont wanna start a pissing match because I know the rad and heater core also have a ton of surface area, but they also have MANY more mechanical connections, not just a pressfit ring with some "hondabond" type sealant

would you be able to post a pic of the rear when you have a chance? Is it evident that the impeller was rubbing it? Maybe the impeller design/depth are incorrect on the reman and it's forcing the cover off

I buy the "ACDELCO" branded stuff off amazon or rockauto and I've had good luck so far. Bad apples come in every crate tho

 

With that many pumps, I think I would’ve cut my losses by now.

The last pump I bought was a Gates pump. No issues in 2 years or so.

Any chance you have a head gasket issue?