Hi Guys,

So I dropped in my fresh 383 last month, did a proper break in and everything is running smoothly. My problem is that when I start it and drive it even the smallest bit, it heats up really quickly and stays hot (reads about 120 deg C on the gauge) So, I checked my temp sender for resistance values and it's reading correctly, gauge seems to work ok, so I think we've ruled out false reading. Also, I had it out over the weekend and after driving about 20 min, I could hear detonation, and when I shut it off it diesled for a half second. So, I think we can be sure it's running hot. It's a brand new rad, 195 deg thermostat, air dam is in place. Not sure what to think. I run about 60-40 water to coolant. One weird thing is that even running at those temps, the coolant isn't boiling in the overflow tank. Any ideas guys? thanks, Ian

 

If the coolant isnt boiling into the overflow, either your overflow tank isnt working right, or the car isnt overheating. Running hot and overheating arent the same thing. 120C is 248F, which is hot, but not overheating.

From the sounds of it, you dont have a cooling issue, but more like an ignition issue. Id double check the timing to make sure youre not running too much advance. Too much advance can also cause the engine to run hot.

 

Sounds like youre not running high enough octane fuel. Whats the compression ratio and octane fuel youre using?

 

Hi guys, thanks for your input. I'm running 91 octane, and my CR is 10.5 to 1. The trouble is the overflow isn't working. I got into it last night and realized I was still running the old rad cap, so I picked up a new one. The old one was obviously seized. However, even running the new one, there was no overflow coming from the rad. I took the car around the block to warm it up, and it got up to about 120 as I mentioned above. Without removing the rad cap, I took off the overflow hose at the rad neck to see if there was even a drip, and there was nothing coming out. I slowly started opening the rad cap, and as soon as any air was allowed into the rad, coolant came shooting out the overflow port. It seems as though I may have a vapor lock or something in the overflow tank that isn't allowing fluid to come through, or even the new rad cap isn't allowing for fluid to overflow to the tank. I'm going to try a new overflow tank cap (maybe the vent on my old one is bad?) or running the car with no cap on the overflow tank at all. Let me know what you think. Thanks again

 

Check your timing, intial and total to make sure its working
Check your cooling system with a lazer temp gun and then report back. I'd bet money your gauge/temp sender is way off.
Also check the air fuel to make sure its not lean.
Is this a carbed car i'm guessing? Are floats to high? carb leaking?

And for cryn out loud, use the celsius to fahrenheit converter so us normal people don't have to and we know whats going on !!! lol

 

haha, ok, I'll convert to Fahrenheit so everyone gets me ok. I'll check the timing tonight and report back. I don't have a laser temp gun, but I know for sure it's running hot. I checked the temp sender according to resistance values and it's reading correctly as is the gauge. Also, I can hear it ping when it gets too hot, and it has dieseled once or twice when shutting it down. I will try and adjust the timing accordingly if it's too far advanced. Also TT350, yes it's a carb'd car. I believe the carb is set up ok, but I can take it apart this week and make sure. Is there any reason you guys can think of that I wouldn't be getting any overflow into the tank?

 

Hi Guys, So this is starting to bug me a bit. I swapped rad caps and coolant overflow tank caps. I was thinking there was some kind of pressure not allowing the coolant to overflow into the tank. Now, unless there is physically something in the overflow tube, there is nothing stopping the coolant from travelling there. I'm interested in the ignition timing argument. If my timing were too far advanced, wouldn't I be hearing pinging? I mean I can rev the car up to 4000 and not hear anything (not that I rev the **** out of it normally, just using that as an example) I haven't gotten a chance to get the gun out and check the timing, but I will this weekend. What ignition timing should I be running? I've heard several different things, up to 8* base, and 30* total...0* base, no more than 20* total... whats the real story? If the timing is out of whack, and that's what causing it to run really hot, that's a simple fix. thanks guys,

 

How much timing you need will be different with every application. You need to set YOUR base timing according to what YOUR particular engine likes, whether that's 8 degreese, 10 degreese or whatever. A friend of mine had a similar problem after doing an engine swap in his truck and it turned out he put the intake gaskets on backwards, idk if that's what happend here, but his would not completely overheat but it ran hotter than it should.

 

Thanks for your input. I don't think I put the intake gaskets on backwards. This is an early style motor, and if you put the intake gaskets on backwards, the bolts won't line up right on the heads IIRC. Tonight I will be checking timing and drilling a hole in the lip of my thermostat. Also, I bought the rad cap as stock style for an 84 vintage 305 motor. Is it possible that it has the wrong pressure setting?

 

So I was reading what you said and you pulled the overflow tank hose and nothing came out til you pulled the cap. Is there coolant in the overflow tank at all? Because there is supposed to be. And the second you pull that line coolant should rush out of the tank. If not then the overflow tank line is blocked. No doubt.


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The rad cap probably won't cause this just being for a 305. The engine that got the intake gaskets on backwards was also an early style 350, he did a 305 to 350 swap. I thought I would just put that out there. The problem your describing sounds very similar to his. He about pulled his hair out trying to figure it out and that's all it was. Good luck with it, I hope its not that.

 

Thanks for the input guys. Yes, there is definitely coolant in the overflow tank. I will pull the overflow tank tonight and see if the line is indeed blocked up. If the rad weren't allowed to overflow, this would cause the problem, right? I'll also be checking my timing to see for sure what I'm running. thanks guys.

 

I don't put any coolant in my overflow tank. My car doesn't get cold enuff to need to draw from that tank.
The tank is only really there to keep coolant from hitting the ground. Radiators used to have a fill line on the tank which was about 1" down.
When coolant got warm, it expanded and filled the rad up without overflowing. If it over heated it hit the ground, that made tree huggers and animal lovers unhappy. Sooo the surge tank was installed.
If your not overheating/loosing coolant, you really dont really need a overflow tank if the coolant is kept about 1" down in the rad..

I agree with Travis401,
I would bet money your timing is off or your gauge is off or your running to low of octane or the floats are set to high or the idle is set to high.
Lots of things to check out other than the overflow. I'd also bet your not overheating if its not pushing coolant out.

 

the rad cap is designed to block the flow from the overflow tank unless the cooling system builds up too much pressure (overheating). thats why theres a little spring on the bottom of the cap. so it sounds like everything is functioning right, you're just not building up enough pressure to bleed off into the overflow tank. which means youre not overheating, just running warm, or have a malfunctioning gauge.

 

Sounds like too much timing to me.

 

Hi guys, got it sorted. It was just a big air pocket I think. I took out the thermostat today and drilled a 1/8 inch hole in the flat section. Put back in with a new gasket and fired up. Ran nice and cool. Timing is 32 degrees total, no ping. Runs nice. Thanks for all your help guys

 

Ok, so the trouble continues. In town now the car runs mint, keeps the temp around 220. Now on the highway is when the temp creeps up. I drove about an hour on the highway yesterday, and as long as I'm moving the temp stays fairly reasonable. As soon as I stop moving it heats up (which is to be expected, I know). However, it does not want to cool down after that, even when I get back up to speed and theres a ton of air going through the rad. My fear is that I'm running lean. I am going to pick up an autometer coolant temp gauge this week to determine if I'm seeing the truth about the engine temp. Also, I'd like to get a wide band o2 and a/f ratio gauge to let me know if in fact I'm running lean. Is that what this sounds like to you guys?

 

What kind of water pump are you running, some years ago (during my divorce years, no money) I installed a cheap pump and it overheated like you are describe (low flow) when at low speed. Is this a serpentine accessory drive system with the correct pump. Serpentine uses a different pump from a non serpentine drive.

 

You can quickly pull a spark plug and determine if youre lean or not.

 

What intake are you using? And is the heater core bypased? If the water pump and intake are plugged and your not running a bypass hose its going to cause exactly what your describing. It will pocket heat, it will over heat at the center cyld's and yet the Rad won't boil over.

 

Hi guys, thanks for your continued help. I read a spark plug according to a gm diagram and it doesn't appear to be running lean (thank god). To answer your questions, I'm using the Edelbrock RPM manifold (non air-gap) and the Edelbrock RPM cylinder heads. For a water pump i'm running the stock small block pump that came on my 305. My car is v-belt driven, not serp. I am thinking that my fan clutch is useless. Not that this would cause overheating on the highway, but it would certainly not help. I'm also not entirely certain that my gauge is reading accurately, so I am going to pick up a good gauge this week and get the real story.

 

A clutch fan can go bad, and can be part of your problem. As can be the used water pump.

 

Hi Johnny, yes I've considered both of those as sources of the problem. I'm going to swap the fan tonight or tomorrow and see how it goes. I'll keep my eye on a 'high-flow' water pump too, something from Weiand or Edelbrock likely. I'll swap to that when I get the chance if the problem persists.

 

OK, is the outlet at the top of the waterpump plugged? Is it run to your heater core or to the intake (small bypass hose) or just blocked off....? Do you have a pic?

 

With the engine cold, remove the radiator cap, start the engine, and let the engine idle for a few minutes to allow removal of any air pockets since it is a fresh engine. With no bubbles prevalent, and with the coolant rising near the rim of the radiator neck, put the cap back on. With the engine still idling, lean over the drivers side fender and blip the throttle a few times while watching the lower radiator hose to see if it collapses under throttle...

 

Yes, i'm running the stock type set up for the heater core. Hoses running to and from the water pump to inlet and outlet. Also, I will do exactly that when I get home Lethal, I was concerned about the lower rad hose too

 

Huh never heard that before, how does water from the front of the intake go through heater core to water pump cool center cylinders? My last 400sbc would jump temp when slowing down from highway speeds.

 

The TPI cars don't even have the heater hose going to the water pump.

That should not be an issue.

 

yeah mine's a carb'd car, so there are simply two hoses. one outlet from the water pump running to the heater core, the second hose running from the heater core outlet to the intake mainfold.

 

OK! Sorted things out. The thing that finally cooled it all off was a mechanical flex fan. I know that there are varying opinions on flex-fans, and I'm well aware of their pros and cons. I put on a Flex-a-lite 1318 (18.25 inch flex fan) with a 2" spacer. This kept my temp below 200 on a 1.5 hour trip on the highway, in town, everything. It was a cold day mind you, but it really kept temps way down. Now, I know what this probably means is that my fan clutch was bad, and never engaging even when hot, thus not providing enough air flow over the rad when it got hot... and that putting on a new working clutch would also solve my problem. But, the flex fan was an available alternative and it works great, so we'll see how it goes. Thanks guys, I hope others have read this thread as well and worked out some of their own cooling issues.

 

i ran that exact fan on my '82 years ago to see if it would fix high coolant temps(220-230) at speed in hot weather-it did,stayed at 190 even at temps over 100*-did well at idle too,though it was pulling a little less air at idle than the clutch fan did.Turned out my air dam was too limber from years of getting bent back and was bending back and ineffective at speed-a slightly bigger and more rigid air dam was built and got my high speed temps down enough(still not as cool as the flex fan though)i put the clutch fan back on as a HP draw was noticed at over 4500RPM with the flex fan.2000 RPM is about the max rpm a clutch fan will engage at,making them ineffective at highway rpm where ram air is supposed to be enough airflow.

 

my 69 327 camaro would run hot (never gave it the chance to overheat), after researching i found that flex fans have a life span. i had no idea how old my current flex fan was so i bought a new one and have had no temp problems since.

 

Yes, I'm pleased with how the flex fan is working. I'm interested with the air dam becoming weak and that being a source of poor air flow. I think mine could use replacing as well, it's cracked in the middle and pretty weak overall. Did you make a more rigid one? and if so, out of what? Fiberglass?

 

I was having the same issue with my fresh 383 build. Running hot is the nature of the beast when it comes to 383s or bigger cubic inch motors. I had dual electric fans on my stock radiator and she would heat up and stay right around 260. I tried a 165 thermostat, that didn't work. I tried no thermostat, that didn't work. I tried larger and more powerful fans and that didn't work.

The issue is the radiator. The stock 2 core copper/brass radiator will not provide enough cooling for that size engine. You need to upgrade to at least a 3 core aluminum radiator. I bought a champion from ebay for right around $300 shipped and it solved all my problems.

FWIW When the clutch in a mechanical fan goes it will stay on at all times it is like a safety net keeping your engine from overheating.

I talked to several engine builders and they all told me I should have started with a new radiator instead of buying all the other stuff. My excuse was that everything else was cheaper than the radiator.

Do yourself a favor and get a new radiator. Here is a great deal on what looks exactly like my radiator.
http://www.ebay.com/itm/3-ROW-ALUMIN...c31e99&vxp=mtr

This is the one I bought.
http://www.ebay.com/itm/1982-1992-Ch...55e8bb&vxp=mtr

 

Those radiators on e-bay appears to be really nice units. I replaced my factory radiator in my '92 Z about ten tears ago with a Modine factory replacement. I have dual fans and the radiator has an aluminum, one inch wide single flue core with plastic tanks. With my pretty much stock set up I have never had an issue with cooling but am prepping the car for a new engine. A 383 is the plan. My question is will my radiator suffice or should I buy this radiator.

 

In my experience probably not. I would suggest building the motor and giving it a shot before dropping the money on a new radiator. Last night I figured I would mess with my car a little and I will say my 383 was running 160* at idle in 97* outdoor temperature. My radiator is about 3" thick and 3 or 4 core. I can't remember exactly, either way you shouldn't have to worry with the bigger radiator.

 

Hi guys, thanks for the continued support. I know this thread will likely help a few other people on the site. I am running the stock-style radiator (a brand new one) and with the proper coolant and air flow, it is working fine. I admit, I am probably running it at it's limit with my set-up, but I guess I'll find out when I track the car for the first time and I'll report back. For cruising, works great. Rad upgrade could be in the works if i find the car get too warm at the strip.

 

I have a 400 stroker in my 89 formula with factory twin electric fans and the org aluminum/plastic rad and my temps run 160-170max any time. No A/C.

 

Good info mine is stock for now but when I do upgrade I will keep the air conditioning.

 

Sorry double post