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Just Bill
09-15-2016, 11:56 AM
57 w/'65 327, +.060, about 10K(16 yrs) on this rebuild. I could not get it to timing right so I pulled front end off to verify timing. No problem detected, so painted, cleaned, flushed the cooling sys before removing radiator(rad new 4 core when engine was redone). Water pump showed signs of leaking so replaced w/similar hi flo pump. New thermostat, new hoses, all shrouds in place. No cooling problems previously. All back together, cools fine idling. When I went up the road, temp spike to 245, dropped back down to about 195, OK for a 1/2 mile, spiked again. Top hose was collapsing but replaced w/ spring loaded type, bottom OK. Still spikes but both hoses OK. The only think I can think of is the pump, but it is a good one from Chevy performance.

Rick_L
09-15-2016, 02:05 PM
The usual cause for quick temperature swings like that is an air bubble in the cooling system. Another symptom that it's an air bubble is that it's something that occurs or is most noticeable as the engine warms up - the temperature will steady out once the engine is fully warmed up.

This is most often seen when Vortec heads or block is used with no bypass hose between the water pump and intake manifold. Older small blocks have an internal bypass so they don't need that hose. The bypass lets the coolant circulate when the thermostat is closed. Since you have an older block and heads you should be good there.

As you surmise, a blockage somewhere could also be the problem. But I don't think it's the pump because the temperature wouldn't come back down after rising.

Just Bill
09-15-2016, 02:23 PM
'65 327/300hp block, '70 over the counter angle plug heads that have always been on the engine since redo, never a problem before. I thought abought air bubbles, but they dissipate over a short period, and the block was full up to the thermostat housing before final filling, the 3rd time. Actually, the only thing different from before the front end tear down is the water pump. I have had 3 thermostats in it, one new temp sensor, and a mechanical temp gauge which proved my electric sensor was working correctly. I am not new to engines, but this one has me baffled, except I don't want to replace the pump....again. A lot of work and it was not cheap.

The temp is fine when idling or sitting w/revs up. The problem has only presented itself once on the road.

chevynut
09-16-2016, 07:34 AM
I fail to see how the pump can cause a spike in temperature unless coolant can't get to it. Don't think I've ever heard of a top radiator hose collapsing, and it's usually the bottom one as far as I know due to the pressure loss in the radiator. Are you sure the lower hose isn't collapsing? Does the temperature change when driving steady, or does it drop when you slow back down?


Actually, the only thing different from before the front end tear down is the water pump.


New thermostat, new hoses...

I'd make sure the lower hose isn't collapsing, by reinstalling the old one or putting a spring in it. If it's not that, I agree with Rick that it's probably air. Remove the thermostat and drive it like that for a while and see if it changes anything. I'm sure there's a simple explanation...once you find it. :)

Just Bill
09-16-2016, 08:06 AM
Both hoses now have springs. but no, the bottom was not collapsing. Temp spikes don't seems to anything to do w/speed. I have a theory, since I thought it odd that top hose was collapsing. Pump is opposite rotation for serpentine belt. The pump is the only thing left, times to tear it apart again.

Rick_L
09-16-2016, 10:39 AM
An opposite rotation pump doesn't mean opposite flow. Top hose should be pressure out, bottom hose should be suction.

Unless...., you have a opposite rotation pump that really isn't.

Just Bill
09-18-2016, 09:16 AM
Guess I opened my opinion before thinking that suggestion thru. Anyhow, I replaced the pump w/basic stock pump, after getting no results from the easy fixes, sender, therm, etc. Works fine sitting in the driveway, now for the test drive. Speculation...the pump was sucking water faster than it could be supplied thru the thermostat, but the new rigid hose should have fixed that, didn't.

Thanks for suggestions, much appreciated!!

chevynut
09-18-2016, 10:42 AM
From what I've read it's not always easy to tell a standard rotation pump from a reverse rotation one without taking the back off and looking at the impeller. Some of the castings are almost identical. I also read that the LT1-LT4s used reverse rotation pumps...could you have gotten one of those? The symptoms of a wrong rotation pump seem to be what you're experiencing, based on some stuff I read.

Rick_L
09-18-2016, 11:45 AM
LT1-LT4 use a totally different water pump than other SBCs. It's mechanically driven off the camshaft, fits no other block than LT1/LT4. And it's standard rotation/reverse flow, the coolant enters the heads first, as opposed to the block for all others.