a strange overheating problem!
Thread Starter
Melting Slicks
Joined: Jan 2003
Posts: 2,877
Likes: 13
From: Doha
St. Jude Donor '08
a strange overheating problem!
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?
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
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.
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
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.
*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.
Thread Starter
Melting Slicks
Joined: Jan 2003
Posts: 2,877
Likes: 13
From: Doha
St. Jude Donor '08
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.
Thread Starter
Melting Slicks
Joined: Jan 2003
Posts: 2,877
Likes: 13
From: Doha
St. Jude Donor '08
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.
*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.
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?
Race Director
Joined: Jan 2000
Posts: 13,024
Likes: 2,266
From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
2020 Corvette of the Year (performance mods)
C2 of Year Winner (performance mods) 2019
2017 C2 of Year Finalist
Same pulleys, fan etc as old engine? You should see water moving pretty decent. Try pulling the T-stat and see what happens.
JIM
JIM
Le Mans Master
Joined: Sep 2004
Posts: 5,116
Likes: 5
From: Livonia MI
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.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
5 Best & 5 Worst Corvette Daily Drivers
Joe Kucinski
The Headlights of Every Corvette Generation Explained
Joe Kucinski
5 Best & 5 Most Overrated Corvette Track Packages of All Time!
Joe Kucinski
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
Drifting
Joined: Oct 2005
Posts: 1,528
Likes: 148
From: East London/SW Essex UK
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!
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
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 ?
Thread Starter
Melting Slicks
Joined: Jan 2003
Posts: 2,877
Likes: 13
From: Doha
St. Jude Donor '08
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 ?
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 ?
Yes I tried to bring up the RPM while in D, and that helped lowering the temp.
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
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.
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.
Thread Starter
Melting Slicks
Joined: Jan 2003
Posts: 2,877
Likes: 13
From: Doha
St. Jude Donor '08
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.
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.
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
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.
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.
