Help with water pump/cooling question...

[gmc67swb]

My truck as of recently has had the temp starting to bounce up and down on the freeway...engine speed is about 2000-2100 rpm at 70mph.(160 t-stat) So I go and get a new t-stat 195*. Put it in and the temp sky rockets! The radiator is a Griffin aluminum unit. If I take the truck out of 5th gear on the freeway and put it in 4th at about 70mph (3000 rpm) the coolant temp drops and will stay low. At idle in the driveway the temp starts to climb past 200*. If I rev the motor to about 2100-2400rpm the temp will go to 190-195*. I've had this setup for quiet sometime with no issues. Do yall think my pump is going away on me? I've never had a pump do that. I've always had them start to leak out the weep hole in the bottom but never loose flow. Has anyone experienced something similar to this?***JUST A NOTE, I'VE TRIED 3 DIFFERENT T-STATS WITH NO LUCK AND THE RADIATOR IS FULL AND HAS NO LEAKS****

[jhwkns]

Check your timing. If it's retarded it'll make you run hot. Good luck.

[72402]

Not likely, but it is possible that the impellor could be slipping on the water pump shaft. I've only seen it happen one time, that was on a stationary compressor engine.

[VetteVet]

I read you post and I am curious as to why you went to a 190 thermostat?
That would make the engine run hotter. The second thing is if you have electric fan(s) and I see in your signiture that you do, then the block sensor could be going bad. I've seen several of these type posts lately and they are all related to airflow and or coolant flow. I would check the sensor and maybe change to a 180 stat. The 190 is too hot for your climate. You can temporarily jump the sensor switch to have the fan run all the time and see if that helps. Increasing rpms will cool the temperature because it increases the water flow so that explains the drop in coolant temperature when you downshift on the freeway.

VetteVet--Just my honest opinion

[gmc67swb]

Thanks for the input Vettevet, one of the three that I put in was a 180. The other two are 160 and the 195*. The fans are cycling as supposed to. I just swapped the water pump and there is a little change but not much. It'll now idle in the driveway at about 205*, but I still get the irradic up and down on the freeway. Also it's only like 50* here today. Anyone else?

[4x4Poet]

Once the engine is up to operating temp, the 195º thermostat wouldn't make a SBC run hotter since they all run at 195º or hotter anyway. Lower temp thermostats only keep the block coolant temp cooler longer during warm-up. An exception is when a poorly made or corroded 195º thermostat doesn't actually open until abovve 200º. That's why I only useRobert Shaw design thermostats, available thru the Mr. Gasket line. Flowkooler still sells RS-branded thermostats. Very accurate opening and closing per temp ratings.

[COBALT]

195 degrees isn't a problem at all. I run those exclusively. The problem is that your temp is bouncing. Your thermostat should be closed when you first start your engine. That means the only coolant moving around in your system is between the water pump and the engine. As coolant starts to absorb the heat from the engine it will heat the coil up on the thermostat, and it will open at the targeted temperature (195). When it opens it will allow coolant to cycle through the top of the radiator, flow down, hopefully be cooled by your fan and running air through the radiator fins, and down through the lower radiator hose back to the water pump, and back to the engine via the intake.

That first line on the temp guage is supposed to represent the warm-up when your thermostat opens (back when the truck rolled out of the factory). Your temp guage should pass this line, and it should go to about the center (straight up) and stay there. If it's bouncing then either heat is building up in the radiator somehow, or the engine, the pump is slowing down, the fan is starting to fail, or your something's wrong with the temp sensor.

Temperature is all about equilibrium, so your guage should be constant after a while. A bouncing guage means the system is trying to equalize, and can't for some reason.

[4x4Poet]

BTW, did you install a brand new water pump when you swapped out the old one?

Edit: I just thought of something else. Check for proper fan cycling per temp rating. Does it come on and shut off when it should?

[VetteVet]

While I don't disagree that 195 Thermostats will harm anything I still believe that a 180 is best for warmer climes. It will allow coolant to flow sooner and help the coolling system maintain a lower overall temperature. I am aware that the newer engines are designed to run at temps well over boiling, I don't believe the older radiators were designed for the higher pressures and may fail if subjected to the use of high pressure caps and higher temperature thermostats.
What's that got to do with the problem at hand. Nothing ! I still feel that the problem is caused by inadaquate flow either because of a failing water pump or thermostat. The fans should have little to do with it on the freeway at speed as they most probably aren't running and would more than likely inhabit airflow to some extent.
All indications are that the water pump is at fault,However I wouldn't rule out a bad temp gauge or sender. I'd also check the wiring for loose connections between the block sender and the temp guage.

VetteVet-- that's my story and I'm sticking to it.

[Fred T]

First thing to do is verify that the temp gage is working right. Stick a meat thermometer in the radiator with the coolant moving to check it. Also, what kind of water pump are you running? If it's stock, they don't move as much water as they can. You can get a plate that rivets on the impeller that will increase the flow.

[gmc67swb]

I'm running a stock waterpump. When I replaced it I got another remanufactured one and put on it. The gauge set is aftermarket. I removed the t-stat all together and ran the truck with the cap removed to verify flow. It's seems to be adequate. On the other hand, with the t-stat installed, the flow is noticably less.

[1-PU70]

Heres my .02 Have the cap checked and then check to see if you have a spring in the lower rad hose.

[69 longhorn]

Is the vac advance on the dist hooked to manifold vacumn? They run a little cooler this way. I agree with check the timing, then look at a flow problem. if you are still running the old V belts, you can swap pullies to change the speed of the waterpump.......remember that the old trucks revved quite a bit more without the overdrive. it may just be that the pump doesnt flow enouhg at lower rpms to keep that perf eng cool. That has a 330hp GM crate......right? 69L