91dime

I will state what my current setup is first;
-2wd s10
-th400 trans
-Blue Print Specialties 350
-Gm Performance serpentine system
-Thick aftermarket alum radiator
-Rigid mechanical fan, no clutch
-Fiberglass fan shroud, covers radiator core

Truck has had an overheating issue at idle for awhile. I always figured it was the fan not moving enough air, so I built a new shroud. Now it moves a ton of air so I will rule that out. Fired the truck up last night and let it warm up at idle. It warmed up fast, I shut it off at 220. The engine was deffinetly hot. The upper radiator hose and that side of the radiator was warm, but the other side of the radiator with the cap was barely warm to the touch. I slowly pulled the cap off(I know I shouldn't do that) and the water gushed out,but it was luke warm.

I pulled the thermostat out, and the truck ran 160. I tested the thermostat in boiling water and it operated fine.

I am thinking my water pump could be spinning backwards? I went by the instructions on the belt routing.

Im at a loss, anybody have any thoughts on what I could look for?

jkris53406

iTrader: (5)

With the cap off and engine running, do you see coolant flowing? The v belt water pumps spin opposite of the serp water pumps, so that is a likely problem.

91dime

I didn't have the cap off with it running. I will check that tonight. I am thinking that it could of been air in the system.

I bought the GM serpentine system from summit, it included the pump. I routed the belt how the instructions said to. I almost wonder if the wrong pump was included in the kit. It wouldn't surprise me, the kit was missing half of the hardware needed to install it.

Bob88GTA

iTrader: (2)

My bet is on the wrong pump

91dime

I wouldn't be suprised. I was not impressed with the rest of the kit from GM. I should of just went to the junk yard for everything. Hopefully I can find a number on it with it on the engine

91dime

Checked the pump #, it works on an 89 camaro 305. It currently spins CCW and that's what the 89 Camaros does too. Now I'm really at a loss. Maybe air in the system I guess.

8t2 z-chev

is the heater hooked up in the truck? Sometimes if there is no "bypass" flow around the thermostat,the thermostat will not open until hot coolant finds it's way to the thermostat wax chamber before it opens-meanwhile other areas of the engine can get good and hot.Sure sounds like a thermostat opening problem since it ran at 160 with no thermostat.If there is no bypass flow provision,a hole of ~1/4"can be drilled in the thermostat flange for bypass flow.

91dime

The heater is hooked up. I do feel like its a thermostat problem too, but its thrown me off because it opened up in boiling water. I will try drilling a small hole in the thermostat, that does make sense. I will do that tomorrow evening.

I ran the truck for a little while today and I didnt really figure anyhitng out. I fired the truck up and let it run for a little while with no thermostat. It was climbing very slowly so I shut it down. I then installed the 180 degree thermostat and started it up. It climbed very quick to 220 again so I shut it down. The engine was very warm, but the upper and lower hoses were barley warm same with the radiator. The heater hoses were as hot as the engine.

One problem I have is that the radiator I have has an offset filler neck, so I cant see flow. Im going to barrow my dads borescope to see if I can see flow.

Im also considering the pump could be bad. I will try the bypass hole tomorrow and use the borescope to see if I can see flow.

Thanks alot for the replies guys!

8t2 z-chev

what intake manifold are you using and where are the heater hoses connected ?

91dime

The intake manifold is a performer air gap knock off that was included with the engine. Hoses are connected to the water pump, and to the intake manifold.

91dime

Well after 3 years off fighting this I've finally figured it out!

Radiator cap!

I bought a griffin cap when I built the truck. I had to have it because it matched all my other blue anodized parts. Well turns out it wasn't compatible with my radiator. I put my cap off of my 96 4.3 s10 on and it crawled to 175 after about 10-15 of running. I'd say the problem is solved.

I did drill a small hole in the thermostat, but I think the cap was the problem.