454 overheating continuing saga

Still don't have a handle on this pump motor. Temp switch/gauge sits at 170 for a while, then swings wildly a couple times and hits the top peg, killing the engine, all in about 5 seconds. Still acts like it's got an air pocket around the sender that moves and slugs the sender with hot water, but the engine isn't that hot. Start it back up, throw the clutch in, pull the throttle back and the temp comes right back down. Bleeding the t-stat and sender before and after it's running. Winding it up to around 3K to sweep the water jacket. Water pump is working. Switched it to vapor and took the hoses off off the vaporizer. Crawled all over it with the heat gun and nothing is out of line. Took .006 off of the heads to clean them up, pressure checked fine, the gaskets looked fine, could not ask for a cleaner water jacket. No joy. Just a couple of times I have got it to stay running, the gauge is all over the dial, up and down wildly, but it didn't shut down, and calms down after a couple hours and works right, well, until you have to shut it down and restart, then I'm back to the same angry rodeo! About all that is left is a water pump that is sucking air or maybe cavitating at an oddly low rpm or a cracked block. Fighting this engine for three days to do a 20 hour pass is really starting to put a layer of frost on my donkey. Thanks for all the suggestion the first time around, I have been hoping for a happy ending to tell you guys about, but I'll have to settle for an update.

I think I would bypass the high temp switch and make it go or blow, but I sometimes make bad decisions. I have a friend with a Cad dvl doing the same thing. I'll let you know if he gets his fixed.

Make no mistake, a "go or blow" scenario would suit me just fine, but if it did blow then I would be in a scramble to find a replacement. I have considered going with just blow many times!

Is there a small drip at the weep hole on the water pump? A mech. told me one time they can suck air thru the weep hole if the seal is going bad. Don't know, just a suggestion. That was on a semi engine.

You sure that Murphy switch isn't bad?

Allan

In other words, screw in a different heat gauge and see if it 'goes wild' also.

Allan

Yeah,may cooler heads prevail or something like that.

Does it heat up when it sits there, If it does open the radiator cap and tie a string on a temp gauge with a probe on in the top of your radiator and manually check it, string is so you don't lose the gauge. You can also buy one of them temp guns at the auto parts but that cost $$. Soil temp gauge has worked to if it goes high enough?

Two mechanical gauges and senders, same result.

Have been all over it with temp guns, everything is right where you would expect it to be. Gets a quick hot flash in the 'stat area when it does it's trick.

I know this may sound stupid, but do you 'spose a 454 could be mounted too level? This one is level, my other one is mounted like a car with the carb flange level, but there are dozens around me that are mounted flat like mine. Maybe some casting flash in this particular head that is trapping a bubble? This is the roller lifter motor without water jacket plugs in the ends of the heads. I'm grasping at straws, but I'm running out of things to grasp, and whatever the problem is it's still out there, mocking me.

The weep hole is dry and the pump appears to function just as it should. It will get changed out next to eliminate that possibility, but I don't think that is the trouble. Hope I'm wrong, chances of that are often very good.

Well the only other thing I had mentioned with a few others is the water pump.

IF that is not it, I am out of ideas.

Assume the radiator is mounted higher than the engine. i.e. no expansion tank on top of the engine. I have seen problems bleeding air on engines with the tank.

To me quick temp swings are air, just a matter of where it is coming from. That is why I keep thinking a cavitating pump, since you have double checked your switches and gauges.

Rick

That's where I'm going next, the pump is moving a lot of water and it's going the right direction but I can not yet say that it's not the problem. No extra tanks, big radiator, top tank is probably a foot higher than the thermostat.

Thermostat checked or replaced? They can cause erratic temp swings

Try it with the thermostat out... Might be it is opening causing a surge...big blast of hot water then cooler water follows

When you speed it up too rpm dose the bottom rad hose suck shut, I had one do that , the spring inside the hose was gone. Put a spring hose on no more heat trouble.

Take a pipe nipple that fits the block where the sending unit is screwed in. Braze the end shut that goes in the block put a coupling on the nipple and tighten it in as though permanent. Mark the nipple for top (high point toward the sky) and remove it and drill a 1/8" hole on the side with the mark (off center to assure air gets out).
Turn it back in (with sealer) and put the coolant back in till it fills the coupling. Then install the dending unit (again letting air out till only coolant is leaking before tightening. This should isolate the unit from swings in temp and air bubbles. Cheap and easy!! Jim

The bit about sometimes if you can get it to run long long enough it will then stay running sounds just like the problems I had with a 391 in a Ford C750. The first time the truck was started for the day the temp gauge would go up, into the hot area and you could hear the coolant start to boil in the engine and push into the bottom of the radiator. If you shut it off for a couple of minutes and then restarted it the temperature would drop back to normal and would stay there all day unless the engine were allowed to cool off. I changed thermostats several times and it made no difference until I switched brand of thermostat.

The problem turned out to be the thermostat in the cab over application was moved a little forward of the intake manifold where there was not circulation past it on the engine side. Since there was no circulation past the thermostat as the engine warmed up the coolant in the heads would get hot enough to boil before the coolant near the thermostat was warm enough to open the thermostat. Shutting the engine off for a couple of minutes when it got hot allowed enough time for the temperature of the coolant to rise at the thermostat so that it opened. Once it opened up and had circulation through it, there was no longer a problem until it closed completely. When I switched brand of thermostat I ended up installing one that had a bypass hole in it. That allowed some circulation past it when it was cold and open at the proper time.

Sure sounds like a steam bubble hitting the sende4r to change that quick.

My best guess is change the water pump, as a worn seal will suck air into the system, especially when you rev it quickly.

Make sure the bypass hose between the top of the water pump and front of the intake manifold is in place with no kinks in the hose or restrictions in the fittings. That bypass is necessary to keep a constant circulation of coolant through the engine untill the thermostat opens. also, is the temp sender in the head or in the intake ?? Being in the intake near the thermostat and bypass hose should help eliminate steam bubbles hitting the sender.

Sounds like a lot of folks offered good advice.....

Here"s mine, perhaps the radiator cap, as silly as it sounds, allows air into the radiator when revved.

If you"ve got another cap, it"d be cheap to try.

D.

I think you have the answers, pump(make sure you get the right one)serpentine drives rotate the other way, hoses sucking in or coming apart on the inside,or the cap. If you can borrow one, put a pressure test on it and look for wet,I have found leaks that would dry as fast as they leaked from the engine heat.

Owen, my old 391 Ford tandem would do the exact same trick as yours!