Well, this is not a corvette, but I really trust on you guys, I just dropped a newly built 355 into my '70 Z28, the engine has a 64cc aluminum heads and about 10:1 CR, the car is running really strong and sounds healthy, yesterday I had the 1st drive-out, and I noticed that the temp is around 200* while driving but it climbs really quickly to 220-230* if the gear is in drive and it would drop as quickly to 200* right when I put the shifter to neutral, I got back home and checked the timing and it was 12* at idle on drive and 36* total at about 2800 rpm, the fan is blowing a lot of air the radiator is almost new 3 core copper, the only thing that I'm suspecting is the water pump, its the same one that came from the tired old engine, before ordering a new one, do you thing I may have a bad water pump which just can't circulate enough coolant while in "drive"?, is there a away I can test that theory?

 

Water pumps usually don't wear out in a way that you can't tell. It makes a bearing noise or leaks, or both. I have seen a couple that had the impeller rust away, but 2 out of hundreds is pretty low odds. Its a cheap enough fix, but I think I would start with the lower radiator hose. Driving your RPMs will be up higher than idling, if the spring is missing from the lower hose it can collapse and cause low coolant flow and higher temps. I don't know if a camaro is prone to bubbles in the cooling system or not, but a 1/8" hole in the t-stst would eliminate it as a problem.

 

Hamad, you likely need more initial timing....When you put it in gear and the idle speed drops, the timing advance drops....Especially if you are still running the vacuum advance...The VA may be dropping out at low low idle rpms and you're loosing your total timing at idle.

*If you are running the vac advance, try hooking it to a manifold vacuum source on the carb(the barb on the plate) instead of the timed vac source....then measure your timing in gear again.

*If you are NOT running the vac advance, bump your initial timing to about 18-20*....BUT you will have to re-adjust your weight/spring combo to bring your total timing back down to 36* (because its gonna jump to 40*+)....

For comparison....
On my 496", I run the distributor locked out at 31*(so this is my initial timing)....and I also have vac advance but I have it limited to 4.5*.......So basically when my car is idling and low engine speeds, I have 35.5* timing.... WOT timing drops down to 31*...

They like a lot of initial timing...You'res probably wont need this much but 20* should cool you down at least 5-10* water temp at idle.

 

SF, I already had a 1/8 in. hole in the thermostat so I don't think its air pocket problem, I also watched the lower rad. hose while revving the engine it doesn't collapse. I also checked the radiator inlet and outlet temps with a IR gun, it I got about 200* in and about 170* out, so I think that would indicate that the cooling system is working fine.

 

I just checked the idle timing without the vacuum advance and it was at *10, I moved it to *18 and will see what well happen, the vacuum advance was already connected to a manifold vacuum source, so it should be OK.

One more thing I've noticed while the engine was running (and it was running for about 20 min. or so, so the thermo. must have been opened already), when I opened up the rad. cap, I saw almost no movement of the water, and I can see the water barely moving at about 2000 RPM, so do you think that maybe the problem? the water pump can't circulate enough water while in low RPM idle?

 

Same pulleys, fan etc as old engine? You should see water moving pretty decent. Try pulling the T-stat and see what happens.

JIM

 

Are you sure that the temp. is really getting that hot? Maybe a bad sending unit, or gauge.

M2C, Steve

 

I've built a few engines and just include new(not refurb) water pumps. Strange hearing about advanced timing, as found it to add heat, and maybe a patch running to much cam for a given head/CR combo. Also prefer a timed port vacuum advance, but opinions vary on this. Anyway, put together a strong set up and runs cool all day long, until stopping for a break and restarting. Seems like the cooling system's somehow taking a gulp of air, and starts running hot. Would appreciate any input on this. Dont think I'm the first one, as seen burp cans availible from Summit and others, but cant say I'm understanding it.

 

If the old water pump has a steel/iron impeller the effects of time, corrosion from lack of coolant and the effects of cavitation can effectively errode the vanes and significantly reduce efficiency. Considering the relatively low cost of a HiPo water pump replace it anyway!

 

What kind of gauge is in the car , electric or direct ?
Have you confirmed with a temp gun that this temp spike is actually happening in the engine ?
Probably a timing and or idle speed issue (flow)but thought it was worth mentioning.

Question-If you power brake in drive to bring the RPMs back up to what they are in neutral does this cool the engine back down ?

 

The car has both the stock temp gauge and another aftermarket one (connected to a temp sender on the dr. side head), and I confirmed them both by using IR temp gauge.

Yes I tried to bring up the RPM while in D, and that helped lowering the temp.

 

Probably just poor flow at idle,we used to put a thin gasket on the back side of the pump to increase idle flow but nowadays the newer pumps are the way to go.

 

Hamad, did the additional timing advance make a difference?

Since you already had the VA connected to manifold vac, you probably already had enough timing advance at idle unless the idle rpms dropped so low that the vac advance lost it's signal and the VA kicked back out. 18* initial should be enough but...you never know. You just have to try different things and see what helps. Like Jim said, check your pullies and make sure they are the correct size and check the stat to make sure it's opening FULLY.

I seriously doubt it's the water pump. They work or they don't. If water circulation is that slow, it is either restricted by something or the pulley sizes are off killing pump speed.

I will say at idle, watching my radiator tank circulate with the cap off, I can see circulation but nothing crazy....it's just kind of pissing out of the top tubes....this is with stock pulleys and an Edelbrock Victor series water pump.

 

I don't know Alan, I already tried different timing settings and I can't really push it more as I have a 10.5 CR and so loud exhaust that I even can't hear the detonation if it will occur.

I'm already replacing the old Torker II intake with a new Edelbrock Air-Gap RPM, so I will just replace the water pump with the new Stewart stage 2 pump and also I'll install the aluminum Becool radiator that I have laying around, then we will see if that would fix the problem.

 

Sounds like your tstat may be closing with increased flow. Your rad temps are good if you are using a 195° tstat.
Like 427Hotrod suggested, pull it out and if you have a 180° tstat, gut it and use just the oriface plate or none at all to test.

The Stewarts 2 pump doesn't have a bypass, so that will help your flow quite a bit by itself, just make sure you have a lttle bypass in the tstat.