I am experiencing what seems to be cooling problems on my rebuilt engine. The temperature raises to about 260 degrees within 10 minutes. By the time it's at this temperature, my short drive has ended and I'm back home. The temp will cool down a bit while idling (about 240* or so) and go up again under load. I have not let it go over 260 degrees.

I rebuilt the engine in my 76 and put in a new transmission. The engine did not need to be bored, only honed. It was hot tanked and had machine work done by a trusted local machine shop. It has the GM vortec 64cc heads on it and I used the summit 1103 cam this time. I used -6cc dished pistons with 4 valve reliefs. There is a new radiator (4-core early 76 style from advance auto parts), new hoses and new ceramic coated headers, practically new everything. The only 'old' part is an Edelbrock 600 cfm carb that was also rebuilt.

I verified that coolant is flowing. The thermostat opens at 180*. It just doesn't seem to be cooling properly. The car has ample power and runs great. I did notice that the catalytic converters are "pinging" and wondered if they might be partially plugged and causing extra backpressure, causing extra heat.

My current plan of action is removing the catalytic converters (will prob replace with high-flow ones after problem is fixed) and converting over to an electric fan setup. I've done some reading on the forums and decided to go with a Ford Taurus fan from a 87-93 taurus. I can buy it new from advance auto parts for a little over $100. (http://shop.advanceautoparts.com/web..._611810715____)

Any other ideas that could help? Thanks! BTW, once this is fixed I'm beginning the new paint job and interior - one thing at a time though!

 

My knowledge is limited to my 1968 SB, I have no experience with 1976 cars, but here are some things to check/consider:

Where is your timing set? If your timing is set at the GM book spec, advancing the timing to more performance-friendly settings will lower your EGTs significantly.

Was all the stock shrouding etc replaced after the engine was put back in the car? Again, this may not apply to your '76, but the shroud, seals and chin scoop are very important for cooling on my car.

Have you verified that the lower hose is not collapsing at high rpms when hot? The stock hose contains a coil spring to prevent this, these apparently sometimes rust away.

Was the sender, terminal or wiring replaced?

Have you verified the temps with an IR thermostat?


My car was running hot; I found that the guage was reading 10 - 20 deg too high, but I still needed to do something. I replaced my original rad with a dual core aluminum, replaced the hoses, added an external trans cooler, meticulously sealed the fan shroud and radiator support, advanced my timing, and replaced my fan clutch. It took all those things to get my temps down to a consistent 180 - 200 deg.

 

Start here.

 

I also have a '76 and I would shy away from an electric set up. Your stock fan and fan clutch will cool things better. I had dual 11" electrics and the car ran upwards of 210 on the highway in summer, now I run 178-180 on the interstate and around 200 in heavy stop and go traffic with an aluminum radiator but I also had the Advance Auto parts one before and didn't have any problem.

I would do what the others have recommended with the infrared temp tool so you know if your gauge is providing a good reading. double check the connection to the temp sending unit then look at the fan air flow when the car is running by putting your hand beind the fan near the carb, there should be a lot of air flow. With the engine off move the fan by hand, there should be some resistance, however if there is none when the engine is cold than chances are you clutch fan is bad.

How far and at what speed are you traveling when you see 260? What was the air temp in your area when this happened?

Something else to think about is the sending unit. Did you replace it? when you reinstalled it did you use teflon tape? it may not be getting a good ground is what I was thinking and providing an inaccurate reading.

 

Thanks for the replies. I'll clarify a few of your questions:

-I'm using brand new radiator hoses.
-I was driving at 55 MPH, ambient temps were around 90*. I drove no more than 15 miles on each trip.
-The temperature gauge is a mechanical aftermarket unit, it's not the original. It worked fine the last time, but I will try another gauge and see if that helps.
-Timing is set at 12* initial with 36* total timing
-I'm using 94 octane gas

I don't have an IR thermometer, so I'll head out later this week when I get time and pick one up. It's probably a good thing to have on hand anyway.

Edit: The new lower radiator hose does not use a spring like the old one did. I was told that the new materials used in hose construction don't require the spring to maintain integrity. I bought it at Advance auto parts, its for the early 76 style radiator, made in US. I checked the hose during the high temps and it is not collapsing.

 

Hmm, this is interesting. You've done everything right and therefore shouldn't be having this problem. You need the lower hose spring. I know the one I bought from Advance didn't come with one so I bought a universal flex hose and pulled the spring out and put it in the new hose. If you don't have a spring then I'd almost guarantee that is the problem. At idle speed it will be fine it's once your driving under a load at higher rpms that it slowing sucks it closed or greatly reduces the diameter choking the water flow therefore cooking the coolant in the block and up goes your temp gauge.

 

Does your rad cap screw on all the way? Is it possible you are low on coolant? It might have air in the system.Run it with the cap off for a while and see if the level drops.

 

The coolant level is good. I had the cap open to check the levels and get the air out of it. Had to top it off a couple times before taking it out the first time.

 

I didnt see any mention of the rad. seals so I thought I would throw it out there. Also do you have the lower spoiler still on? It seems funny it would start to cool at idle?

 

Just wondering aloud. Maybe someone else could correct me if I'm wrong.
Might the "new" engine be happier with a richer carb calibration than the old one? If you changed many things (compression ratio, cam, heads, maybe) the carb jets and rods may need to be changed to give it a scoosh more fuel..
Or theres a big &*%# vacuum leak, and that's making it run lean..

 

When I rebuilt my engine this spring, I replaced the temp sender with a new one from Summit Racing. Just like you, in 10 minutes the gauge was at 240. Beat my head in trying to find a problem.

My perfectly calibrated fingertips didn't sense the temp being much over 180 (thermostat setting). I ordered a new temp sender from Corvette Central. Plugged it in, and the gauge is solid at 180. Also, I have an electric fan with a 190 turn on temp. When I shut the car off, within 5 minutes the fan turns on as I expect it would. So my gauge is accurate now.

First place to look is the sending unit.

Then (I did this once, so no assembling engines at 11 PM), check to make sure the fan is facing the right way. There is a FRONT face to the fan.

 

How far is it bored out?

 

The block has the standard 4.000" bore, it was only honed.

I did some more research online and found some others that installed Vortec heads had this same problem. Running a bypass hose from the waterpump to the intake manifold solved the problem. According to the posts I read, vortec heads do not have a bypass provision like older heads do.

I'm going to try this and see if it works. Probably won't get any time until this weekend, but I will update and let everyone know if it works or not.

Edit:
(Here's a picture of an example of the bypass hose and a quote from the guy that posted it)

http://lh5.ggpht.com/_TjlLd8h6Fis/TF...2/IMG_6761.JPG
http://coloradok5.com/forums/archive.../t-273933.html

 

That's pretty much like the BBC's have, no internal bypass like the SBC.

The BB has the hose on the front of the intake for its bypass.

Its common for people to cap them off on a BB, I tried to cap mine off and experienced temps that would spike and run high randomly as indicated in the discussion following the link you posted.

Neal

 

I have fought with this issue in my Silver Anny for years, its' chronic in C3's.

If it has the original cam profile, they will run hot by design. They have tons of overlap and GM set them up hot out of the factory to help meet the original chaos of emisions standards. The higher temps helped to burn off more hydro carbon in the exhust and cat system. The H/L83 can run hotter if the EGR is removed, especially these days because it's hard to get REAL 96 octaine: They detonate at high heat and the hotter they get the worse it gets, a run away effect. Detonation = Heat, lots of it. The EGR was designed to quell knock (Detonation) and is NOT a bad thing. Less knock, less heat, simple math. Properly functioning, they really don't effect performance all that much. O.K., there is a little loss, so Johnny law only gets to write you a ticket for 110 insted of 112 in that school zone... with a hand gun, an 8 ball and a $50.00 gin buzzzzzz.... sucks to be him, eh? (Just kiddin' ; or is he??)

So what's a po' boy gonna do?

Simple stuff like glazed belts and pullys are always on the menu. My idiot brother fought with a charging system issue once, repeted alt swaps, dead batterys, fusable links. Weeks of frustration all for a $10.00 belt. Lesson learned.

If you are running the stock distributer be sure that the advance (vac and weights) are not stuck. That will raise hell. And double check the base timing as well, try and add or subtract a degree or two, see what happens. The scale and/or harmonic balancer might be off. Just don't get too carried away. Listen for knock, that is important.

Be sure that you have good shroud and hood seals. The pressure tends to equlize front and back of the rad if you dont. Cheap and easy fix.

You need a good air dam under the front clip. Any real dammage there will cause issues. Be sure that bugs and leaves are not blocking up the front intake and rad and/or evaporator, (if you have AC) and check 'between' the evap. and the rad. for junk running defence.

Sure, that rad looks nice outside, but what is going on inside? Auto parts biggies are cutting each others throats, you know who looses in that battle, mr quality, that's who. Always suspect cheap stuff. Rads. get cancer all the time, if she is a relic or not, think about a new one. There are lots of choices there and you get what you pay for and pay for what you get.

If you removed any plastic covers or dams from under the hood you need to put them back on. Even the one that hangs over the core support. You want as high a pressure as you can get in front of the rad and as low as you can get behind it. Plug all the holes, I love black racing tape for this job. And if you do it right, it looks pretty good. If you pulled the theromastat, it helps to gut it and run just the frame, not the guts. Coolent can pass to fast through the rad and actually work aginst you.

Header tape will cut down under hood temps but it doesnt last long and seldom looks very good.

A good flush and refill never hurts and there is a product called Wetter Water that transfers heat better. If that temp guage is still looking like something out of the control room at Fukashima, this is the real deal: A DeWitts rad. and fan set up... it's the holy grail and will square you up with a simple retro fit. http://www.dewitts.com/, It's theeee cure if you have an extra 'G' burning a hole in your pocket.

 

That bypass hose recommendation is BS. I've had Vortec heads on my 383 for 5 years, with no bypass and both heater hose connections plugged. I have no cooling problems, even drag racing in summer weather conditions.

 

 

GM vortec 64cc heads use a different temperture sensor, because the hole size is smaller.
You may want to consider placing you orginal Temp sensor in the intake manifold, to see if this will correct your readings.

 

Willcox's has good info.http://willcoxcorvette.com/repairand...lp.php?hID=167

 

i vote temp sensor is off.