NOTHING else was changed.......swapped a 350 with 305 heads into my girlfriends camaro, and now it overheats after 15 minutes of driving. Has the same 160 thermastat, same carb, same intake, same radiator, same everything. Previous motor was a 305 with a 262 comp cam, new motor is a 350 with a 268 comp cam. And the compression isn't THAT high.......its around 9.5:1 with the thick head gaskets. Water pump is the same from 305.......I don't get whats happening. Timing is right on the money......and nothing appears to leak. This is in a camaro by the way and the fan is wired to run all the time. Car will run at 180 for about 10 minutes, then it will gradually creep up and up and up past 220 till it overheats. This sucks! Whats happening?
Chris

 

Ok I lied, I changed ONE thign......but this shouldn't matter.....I dont' think. I deleted the heater lines, had to block them off because the headers wouldn't fit with that hard line that runs near the passenger side frame rail.

 

You put 305 heads on a 350? 9.5:1 ??
Unless somehow you screwed up the heating so the intake is not discharging into the radiator. I'd blame compression. whats your PSI per cyl?

-- Joe

 

compression?

 

Compression is not as high as you think..........my friend did the same exact thing with a 350 he built......except his 350 had FLAT TOP pistons, this one just has dished pistons, and his ran just fine. I'd say 9.7:1 at the highest.

 

things you can do. Get a different calibrated thermistor/temperature guage. A digital one should tell you what temp you really have. If its really that high now, then get a higher flowing pump.

 

If they're really 58cc heads (most 305) its gonna boost the compression up like 3 points.

-- Joe

 

Back to the main question, have you made sure that ALL of the air is out of the coolant system? Maybe you need a new radiator cap. When I threw in my 355 (with 305 heads 2.02/1.60 valves ,flat tops w/ 4valve relief ) I had the same thing happen during break-in, shut it down 4 times, man I was bummin, my thermostat took a ****, then when I thought the coolant was totally flushed of air, it was'nt. I had a major air lock going, once that was burped everything was ok.

 

Bought a new radiator cap.........reinstalled new heater hoses, refilled coolant with engine off and while running to ensure that it was entirely full.............and checked to see if thermastat was working......it was. Car still goes to 220+ after 10 minutes of driving, and gradually overheats....and this is driving it at night, not during the day, hell, during the day I wouldn't even dare driving this car around the block!!! Damnit I'm getting really frustrated. Is it possible that the 3000stall converter I installed in the car heats up the tranny which in turns heats up the radiator a tad too much?? Would an aftermarket tranny cooler work better than the factor in radiator cooler?

 

Had to reread your first post, it says you have the FAN wired so it's on all the time, I'm assuming single fan, right? If so, that was another upgrade I HAD to make, swithched it over to a dual fan set-up off an IROC and they're both wired to come on at 160. How new is the motor, they always run alittle warm for awhile till things get seated, maybe a couple good days of driving. If you have the air dam under the front, I can't think of much else as it sounds like all bases have been touched. Maybe turn the timing back a little bit, does it seem to deisel when you shut it down? Sometime too much advance will make the motor a little warmer, I had mine down to 28 degrees total just so I could drive around and get some break in miles on it. Maybe the radiator tubes are slighlty clogged, did you try spraying water into the radiator fins and cleaning out all the road dirt, that will help a little. If none of these things work I'll be as stumped as you are. Could be another faulty thermostat, I went through 3 in 1 day on my truck till I got one that functioned properly. Good luck!

 

Have an 88 that I bought from a dealer who changed the 305 to a 350...reusing EVERYTHING. Had a problem with overheating just like yours ...after about 15 minutes running, it would even start to boil out the overflow tank. (I did have to replace the injectors to pass emissions test from 19lb to 21 lb, but everything else was reused...6 attempts at the new Texas state emissions test....)

new stat didn't help, replaced the temp control sensors, checked the operation of the fan relays, new rad cap...nothing helped.

finally replaced the stock alum/plastic factory raditator with a 3 core copper/brass from 1-800-radiator and no more problem.

i know a lot of the guys(and girls....MUST be PC here) tout the stewart 19/31 aluminum radiator, always on fan switches, etc, but the one thing that fixed mine was replacing the radiator with a new one and one that had more cooling surface to it...go with the stewart or even to autozone and get one....but get yourself a new radiator...one for a 350 engine...that stock 305 plastic / alum one ain't cutting it and no telling what kind of junk it has inside ....

 

Checked your timing??? Retarded timing will cause an overheat condition.

 

Replace the Radiator, or at least have it checked out by a good shop. Next change the thermostat to a 180* and drill two 1/8" holes around the edges to help purge the cooling system of air.

 

Right on the money? You verified this how? Timing gun / balancer / timing chain cover mark?

If any of those are off you're screwed. You're probably not using the 305 balancer, so who knows if the balancer is spun or what?

Set the motor to 0* base timing then pull the cap off and see where the rotor is.

 

is it running extraordinarily lean?

 

Thanx for all the tips guy, conscensus seems to say that I will be buying a new radiator next paycheck instead of buying a Demon carb for my Formula Non-performance mods suck! Though keepin the car at 180 should make it a lot faster than running at 220 all the time.

And timing is right on the money as verified by the fact that I rebuilt the motor, installed the stock 350 balancer onto the crank snout with the #1 piston @TDC, verifing correct 0 placement on the timing tab, and timed with a craftsman $100 dial back timing light. I'd say its right on the money

 

Yep, it does sound like you've got the timing issue under control.

 

Is the fan rotating the right direction?

Will it overheat while driving or just when idleing? If when idleing try to rev the engine as the temperature starts to climb and see if this helps it or makes it worse.

You said the timing is on the money but what is it set at?

 

eric read his reply on timing ....2 posts up from yours....

 

justadba, I did read the post and it doesn't say what the timing was set at with the $100 dial back timing light.

 

Well, its set at the tried and true 36 degrees total that I have all my other cars set at and seem to make best 1/4 mile times at. I would hardly think thats too much or too little timing. It couldn't be the timing because with the 305 I had the same exact timign curve (same distributor) and it didn't have any kinda problems. I'm leaning towards buying a new stock 3 row copper radiator I guess.

 

If you are on a tight budget, you may be able to get away with just getting your stock radiator cleaned out...or flushed. It still won't cool as well as a 3 core radiator...but it should help the situation some

I have never used the 1800 number one guy referred to, but i have a Azone 3 core radiator in mine and it works great...w/lifetime warranty! You can also get a Modine from Adv. Auto and might be able to get them to match Azones price if there are both in the area.

Something you might want to consider..with 305 heads(not sure why you did this as 305 heads have PUNY valves) you raised your compression as everyone has said...but you have also introduced lots of sharp edges to the combustion chamber...since the 305 combustion chamber is actually 56^(VEtte alum. heads are 58^)...thus your engine will be more spark knock prone...I think you should maybe dial that timing back to the 28^ someone else mentioned....then gradually increase it until you get knock, then back it off.

Good Luck,

 

The reason of the over heating is because of the 305 heads. You can do all the work you want to solve the problem like installing a better thermostate, rad, fan but it's all in the heads. cylinder heads that is

the 305 cylinder heads have smaller water jackets then the 350 which causes it to overheat. If you really want the compression for the motor with stock pistons then just continue swapping out parts till you lower you temp.

just my .02 cents

good luck

 

I thought that's what he was doing?! The 305 heads may have smaller water jackets, but how many people that do this swap everyday for cheap HP and don't have temp problems. I have 305 heads on my 355 and mine runs 160 all day, jumps up to 180 @ 100 ambient temp in stop and go traffic, and no higher.

 

Chris, what is the timing set at @ idle? My car and many others have had this same issue. It may only be off several degrees to have these symtoms. The timing may need retarded some with the higher compression. Give it a try. Make sure the advance weights are not swinging out any at idle.

 

Here's why: the heads were completely free and it was either free 305 heads or garbage 1.72/1.50 valve late 70's 307 heads. Hmmmmmmmmm...............305 heads aren't as bad as everyone thinks. I got the camaro to run 14.0 EASY my first try with the new motor and it'll easily go 13's once I work out the carburetor and overheating bugs and learn how to shift with the stock crappy 700R4 shifter. I think I'm going to go with that Azone 3 core. Thanx for the advice guys.

 

Well, heres some more info. I also have a 355 with 305 heads in a 84 Z28 and I used them for the same reasons $$$. Heres what your comp. is.

Bore = 4.03"
Stroke = 3.48"
Head cc's = 60 (3 angle & ported)
Piston valve reliefs = 4cc (Flat top)
Deck Height = .025"
Head Gasket = .038" (Fel-Pro)
Head Gasket Dia. = 4.166"

The Compression Ratio Is 10.36 to 1

I set my timing at 6* at idle which = 34* at 4500 rpm and use a knock sensor. Oh and I did not do anything to the stock 305 cooling system and I have had no problems except when my stat stuck shut. I hade (4) .200" holes drilled in the stat and thats what saved the eng. Needless to say I have them holes in my new stat.

Auggie

 

Don't know if this has been said yet but you better get an aftermarket tranny cooler if you're running that high a stall converter.

 

Ok here's an update:

Got a new Griffin 31X19 aluminum radiator, installed flexilite 24,000 GVW tranny cooler, backed off timing a couple degrees to 32 total. Guess what, STILL OVERHEATS!!!!!!!!!!!! #@$%)(@*%#LK@%J%JK B:%J%JK #@KLV **** I give up. anyone want to buy an overheating POS? (lol that would make it steamy ****)

I really don't know what else to do other than to install a mechanical clutch fan which I can't believe I"m resorting to. All my other cars with MORE HP and less grill area don't overheat with an electric fan the same size.

 

Chris... take a step back for a moment.

You still have the same water pump. Is it possible that it's on its way out?

Could you have possibly plugged any of the coolant passages in the motor?

If you've got a single electric fan, let me tell you that when it was hot out my ZZ4 would do exactly the same thing, overheat slowly. The single fan just doesn't move enough air. Especially not if the fan motor is marginal! My friend's 92RS had exactly the same problem with the STOCK LO3 and it was because his car had a cheap POS aftermarket replacement fan motor that was on its way out. I gave him a 14 year old fan GM motor from my old single setup and his problem magically went away.

I still have the stock L98 radiator, but I have dual electric fans and a stewart stage II aluminum pump. The fans were actually what kept the motor cool for me. The water pump came later, and helped some, but I don't think it could compensate for not enough fans.

Does the car cool sufficiently on the highway? If it does, you're looking in the wrong place. The ONLY thing that can cause a car that runs cool on the highway to overheat badly in traffic is not enough fannage. Honestly think about replacing the fan motor at that point, because it could "work", but not be moving enough air to do the job. Feel the fan motor, if it's hot to the touch, then you NEED a new motor. It should be cool to warm--hot is a sign of a motor dying.

 

Chirs, forgive me for not reading through the 40+ post's but which head gaskets did you use 305 or 350 and are you certain they were installed correctly? It may seem dumb to ask but a flip flopped set of gaskets would cause this problem "done 4 of these setups myself" and If you use the 305 head gaskets you could run into a cooling issue. Also the electric fan may not be pushing enough air. I know you mentiond you did not want to go to a clutch type setup but they do cool more consistantly. Also some cooling systems operate at a more stable temprature range with a higher temp thermostat allowing more cycle time for the water. Ive seen it 1st hand with a 50ft motorhome the dirt SOB ran hotter with lower temp thermostats, 220* with a 180*, 230* with a 160* and with an OEM 195* it never got over 210*.
Other than what I mentioned these guys have the only obvious thing that could be wrong and thats timing. Since your now running a higher compression engine the octaine needed is higher and in order to use El-Cheapo pump gas the timing has to be retarded or the octaine rating must be increased. Ive found with a moderate advance "10*" I can run midgrade fuel with little or no detonation on a 12:1 engine, of course the power isnt quite there untill I go up to 13*+ base timing but higher octain fuel needs to be used or the engine will run into detonation and run hotter.

Just some thing to think about

 

I experienced the same issue with my Nova, putting 305 heads on my 307. It turns out the coolant passages in the 305 head are smaller and do not perfectly align with the passages on the 307, a little less diameter, which restricts the coolant flow increasing heat and pressure in the cooling system. Went to earlier model 68-72 350 heads that ended up having slightly larger valves anyway, and cooling issue went away. The rest of my cooling system was already new, including radiator, water pump, T-Stat, hoses, belts, etc.