labrat Posted October 11, 2002 Share Posted October 11, 2002 I just got a quick question here, folks. My car has been overheating on the highway ( no problems around town) and i suspect my lack of overdrive coupled with a restricted 2" single exhaust may be part of the problem. I have already split one of the seams on my muffler, and plan to redo the entire thing anyway, but I want to take care of my overheating problem ASAP. Could they be related? Will a larger fan/rad combo take care of the heat or should I just redo the exhaust and see what happens? I will have to drive this car to work intermittantly, so I'm looking for reliability rather than horsepower at the moment. Any and all input is greatly appreciated! Bill Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted October 12, 2002 Share Posted October 12, 2002 I would suspect inadequate air flow. Usually sustained highway driving (I assume at near legal speeds?) is the last place people have cooling problems. A couple of previous post cautioned that the lower radiator hose can "collapse" with engine speed severely restricting coolant flow. If not that, then (my guess) you aren't getting enough air flow THROUGH the radiator. Make sure the radiator is tight against the body work so air cannot flow around the radiator instead of through it. A belly pan (I think it is called a chin pan) mounted between the frame rails beneath the radiator also cuts down on turbulence underneath the car. This help smooth the flow of air through the radiator and is a known cure for overheating in the early Z's. Available from MSA. Besides that, check the obvious stuff. Radiator full? Radiator cap in good condition? No fluid loss (which means you could have a leak that prevents the radiator from being presurrized)? When was the last time you flushed the cooling system. Water pump making noise? Thermostat in good shape (put it in a pan of hot water to see what temp it fully opens)? Ignition timing set properly? Seems like guys are quick to put in bigger radiators but sometimes that is just masking a more basic problem. Quote Link to comment Share on other sites More sharing options...
labrat Posted October 12, 2002 Author Share Posted October 12, 2002 Well, I know my lower rad hose isn't collapsing, its the spring wound flex type hose. My water pump, thermostat, and radiator are new (well, boneyard rad, but I flushed it with muriatic acid before install), and the block has just been vatted when I rebuilt it. I'm running the most timing I can without getting starter kickback when I try to start it. New distributor, mechanical and vacuum advance all working properly. I don't think I'm losing pressure, seems to build that up fine. It's an 81 ZX with a 350/th350, and I thought my 3.90 gears and highway revs (yes, at near legal speeds... ) were just making more heat that the rad could dissipate. I think I agree with you that it's not getting enough air through it, though. It used to have a small belly pan, but I've lost it during a couple of moves, I guess I'll find one at the boneyard and see if it makes a difference. I'll also try to seal the rad to the body with some flexible metal tape and see if that makes a difference. I agree its a weird problem, most people overheat at idle. I just wanted to know if my restrictive exhaust could also be a contributing factor, holding more heat in the motor as the hot exaust gasses can't exit easily. Thanks for the reply! Bill Quote Link to comment Share on other sites More sharing options...
Guest greimann Posted October 12, 2002 Share Posted October 12, 2002 Maybe you could run down exactly what radiator and fan situation you have now. Has this been a problem before or has it just recently occured? Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted October 12, 2002 Share Posted October 12, 2002 Just a Idea that worked for me. I went to Home Depot and bought the 2 by 2" or 3 by 3" foam strips in 3' length and put it around the edge of the radiator and radiator support to make a tight seal. (crushed between the two) Man what a difference it makes. Forces that air thru where it is needed most! Just an Idea that worked for me. Dropped temp 10 degrees! Mike Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted October 12, 2002 Share Posted October 12, 2002 Bill, for an experiment, run the hood unlatched to see if allowing more air out helps the cooling. I have a theory that the Z does not let enough hot air out. Quote Link to comment Share on other sites More sharing options...
labrat Posted October 12, 2002 Author Share Posted October 12, 2002 Well, when it gets to the point where it starts getting hot, usually my first crutch to find an exit is to pop the hood and run it about 1-1/2 inches open at the back. Yeah, it seems like the air just doesn't have anywhere to go. I think the engine compartment may be pressurizing, causing less air to flow through the radiator. I'm using a radiator from an 88 buick regal (26" wide by 19" tall 2 core copper) and an electric fan from an older ford taurus, not the 2 speed one. With this paycheck i'm thinking about going to a griffin with a black magic fan, but I need to definitely fix the problem, not just throw more parts at it. I've tried a couple of different junkyard radiators, all they've got me is a garage full of radiators. I think I'll get the griffin and fan, seal it up good to the bodywork, and add a belly pan and see what that gets me. I also have some water wetter stuff that says it'll reduce temps by up to 40*, maybe with all that it will solve the problem. Then, I may be able to justify a front spoiler to my S/O. She won't let me spend money on looks yet, not till I get it reliable. This will just give me an excuse. Thanks for the input, guys! Bill Quote Link to comment Share on other sites More sharing options...
Z-TARD Posted October 12, 2002 Share Posted October 12, 2002 I seem to remember reading in one of David Vizards engine books that an engine loses up to 1/3 of the heat it creates through its exhaust. That would make senses to me since you are overheating on the highway, where your engine is running at higher rpm and creating more exhaust. Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted October 12, 2002 Share Posted October 12, 2002 I think a used, 2 row copper radiator might be marginal. Do the obvious stuff first and if that fails drop the $$ on a griffin. Or even recore a stock Z radiator to a 3 row. There are guys on this board who have no cooling problems with that set up. The big issue with a 3 row copper rad is weight. Normally I go I tirades about electric fans (I am personnaly convinced they don't cool as well as mechanical). But in your case I don't think the fan is the issue since you are overheating at speed and not in stop and go traffic. I think you are right. Too low of gearing will definitely add to your heat load. The exhaust I am not as sure about. But either way, you aren't doing anything so out of norm that your cooling system shouldn't be able to handle it. Somewhat unrelated but you might search though the old postings for an article someone posted about Z car aerodynamics. To paraphrase, this article said the Z grill opening was too large thus letting too much air build up in the engine compartment. They were talking mainly about this causing the excessive front end lift. But the intersting thing is they maintained the Z would have better cooling efficiency with a smaller grill opening. Something like a G nose. Quote Link to comment Share on other sites More sharing options...
labrat Posted October 12, 2002 Author Share Posted October 12, 2002 Well Jim, I agree with the electric fan part, but a mechanical flex fan would stick about 2" out the top of my hood with my engine placement (had to clear the power steering gearbox with manifolds) and this was my only choice. The reason I suspected the exhaust may have something to do with it is because of the speed at which the temp climbs when I get on it. 5 seconds of throttle equals 20* spike in temp. As long as there are lots of traffic lights around to let me cool off between bursts, i'm fine. As soon as I accellerate (Or maintain highway speed) the temp shoots up like a rocket! I can't get 2 miles down the highway before temps start hitting 230+. And they will climb all the way up to boiling if I don't stop, they won't just settle down a little higher. I had this problem before, blamed it on blown headgaskets and rebuilt the motor. Got a nastier cam in it now, and it does it worse, that's why I suspected exhaust related. And when I say restricted exhaust, I mean I split a brand new muffler at the seams in under 1000 miles. WAY restricted. That's why I was concerned. I am just going to pony up for the griffin and hopefully not worry about this EVER AGAIN! It's been plagueing me since february, and i'm tired of it. Getting rid of my d*$& points, too! Bill Quote Link to comment Share on other sites More sharing options...
Guest DRK Posted October 13, 2002 Share Posted October 13, 2002 Set the timing to a more stock setting and see what that does, And uncork that exhaust. DK Quote Link to comment Share on other sites More sharing options...
Mike C Posted October 13, 2002 Share Posted October 13, 2002 Bill, you should definitely get your points situation under control. Ignition timing has to be spot on before you can spend any time at all on other woes. I know when we were monkeying with it before, that point set you had was WAY whacked. They work quite well if set correctly. You can get a set of Blue Streak points for about $8 or a set of Accels for $14 or so. The 9.8:1 331 in my Jimmy had an LT-1 high rise with a 70 Z/28 780 Holley and a Cam Dynamics (now Crane Energizer) 284/284 .480 cam. I ran the truck 2" rams horns and a single 2" exhaust. With NO overheating problems. (It also had a stock points distributor because of firewall clearance issues.) I was broke and in college and it was the old motor from my Camaro that was in the garage when the originally one in the Jimmy expired. Admittedly, adding a set of headers and 2 1/4" exhaust was worth probably 80 horsepower. I find it hard to believe it's the exhaust, but fuel mixture (unlikely with the 750 but you never know...) and ignition timing are most likely the suspects. I'll still put the dwell meter on it if you'll get a set of points. Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted October 13, 2002 Share Posted October 13, 2002 Aliright, lets put 2 + 2 together. You have a split muffler and points problems. Hmmmm. 2 + 2 = Backfire! I was just thinking there is no way your engine would run if the exhaust flow were so restricted that the back pressure could split a muffler. Misfires definitely will. Had a buddy back in high school who reached over and turned off my ignition while I was driving. That was bad enough, but before I could stop him he turned it back on. With the ignition off, the exhaust system filled with 14.7:1 air fuel mixture. When he turned the ignition on the whole thing went off like a fuel-air weapon. In this case it actually blew the exhaust manifold off the head. Do as Mike C said and fix what you know is wrong first before tackling other problems. Quote Link to comment Share on other sites More sharing options...
labrat Posted October 13, 2002 Author Share Posted October 13, 2002 Well, I got new points the other day, and set the dwell by a method I got from ignitionman on chevytalk.com. The ignition system was so bad it wouldn't even putt around the block without spitting and sputtering, so I replaced em about two weeks ago. Thanks for sharing that story about your exhaust, I don't feel too bad now. The exhaust will get uncorked next paycheck, and I will get my accell billet hei, but right now my cooling problems have the priority. I know all this stuff has to get fixed, and i'm willing to put the money up for it, I just can't right this minute and I have to prioritize. I was out of work for almost 2 months, and I just started working again 4 weeks ago, as soon as I get caught up on bills and utilities, the Z is a go. Thanks for your offer, mike, I really do appreciate it, but i'm working and going to school now so I just have to grab a few minutes of wrench time here and there when I can. I'm sharing my girlfriend's car with her right now, and would like to at least get this thing running enough to get me back and forth to work on the days our schedules conflict. I thank everyone here for their contributions, I will back that timing off a little and recore my existing radiator at a rad shop and buy a black magic fan and see what happens. Bill Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted October 14, 2002 Share Posted October 14, 2002 May want to read past posts about black magic fans. If I remeber right people have had problems with that one. Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted October 14, 2002 Share Posted October 14, 2002 Do the exhaust first. Get the points straight. Then maybe the radiator. I'd change the fan too eventually if it cannot keep it cool at idle. All in all I think it's the exhaust... Quote Link to comment Share on other sites More sharing options...
Phantom Posted October 14, 2002 Share Posted October 14, 2002 OK - to sum up it appears that the following has been suggested: 1) Open up exhaust to 3" single or 2.5" duals. 2) Seal any open areas around radiator 3) Get a belly pan under the engine bay 4) Get the timing right/fix the points/the new iginition After that, evaluate if you need a new fanor radiator. Quote Link to comment Share on other sites More sharing options...
Guest greimann Posted October 14, 2002 Share Posted October 14, 2002 If you are going to get a new fan, go with the Taurus fan because that fan on low speed cools better than the Black Magic. High Speed is cat 5 hurricane stuff! For the same price as a Black Magic, you can buy a new Taurus fan at: Taurus Fan Quote Link to comment Share on other sites More sharing options...
pparaska Posted October 14, 2002 Share Posted October 14, 2002 Forget the Black Magic fan. The Taurus one is much better. If you have to stay aftermarket, get a big Spal fan. Also, make darn sure you have no air in the system. Before I got all the air out of the coolings system, my Z would register 20 degrees too high. After cycling the heater core valve open and closed about 20 times while cruising, and keeping the recirculating overflow bottle topped off, I got all the air out. I would be cruising down the road (had lots of time - going from DC to Atlanta a month ago ) and saw the temperature creep up to 220 or so. It seemed to do this as the car was going up and down small hills. So I began to visualize the temp sender getting uncovered as the car's pitch changed. I knew that sometimes cycling the heater valve opened and closed could move air bubbles around, so I tried it. As soon as I opened the valve (moved the dash lever from cold to hot) the temperature plummeted 20 degrees or more. Then I'd close it again (put it on cold). A short time later the gage would read high again, so I repeated the process. This went on for an hour. After shutting down for one of my many gas stops, I guess the system purged the air and sucked some coolant from the recirculating bottle. After that, it never read above 195, which is the temp of my thermostat. The moral is : if the sending unit for the gage is not in the water/coolant, it'll read higher than the water/coolant actually is. Quote Link to comment Share on other sites More sharing options...
labrat Posted October 14, 2002 Author Share Posted October 14, 2002 Getting the air out of the system has also been a problem for me, the filler cap is lower than the upper radiator hose and manifol. I actually removed the radiator from it's supports and lifted it above the engine while it was still connected via hoses to fill it, and it still gave me problems. Not running any heater hoses, so I know that's not an issue. Hmmm.... This cooling system thing is a nightmare! Easily the most difficult part of the swap. Thanks for all the input from everyone involved, I feel like you guys are just one big happy helping family! Bill Quote Link to comment Share on other sites More sharing options...
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