Zfan1 Posted April 29, 2015 Share Posted April 29, 2015 Anyone else have this problem? When it's cold out I have no problems with it running cold at most any speeds but when it heats up it runs hot at freeway speeds. typically 180-190 around town in stop and go, 200-210 at 65-75 mph. I believe I may have an issue with the cowl hood building pressure under hood causing turbulence issues thus causing the cooling system to lose efficiency. I am thinking of blocking the under side of the cowl off from air flow and seeing what happens at freeway speeds or just replacing my cowl hood with my stock louvered hood and not messing with the whole mess. I would like to add a/c to the car but I must first get the temp under control before ever tackling the addition of a/c. Quote Link to comment Share on other sites More sharing options...
Phantom Posted May 5, 2015 Share Posted May 5, 2015 Mike, I have never had an overheating issue - even in Dallas when it was 100 out, my AC was running full bore, and one of the cooling fan relays went out. 280Z radiator recored to 4-rows and '98 Z28 fans and shroud under a stock '77 louvered hood. Doesn't matter if I'm in stop-n-go or barreling down the freeway. Quote Link to comment Share on other sites More sharing options...
Zfan1 Posted May 5, 2015 Author Share Posted May 5, 2015 I am on the fence as to what way to go but stock louvered maybe just the way to go. I like the idea of cool temps especially since I will be adding AC too! Quote Link to comment Share on other sites More sharing options...
Phantom Posted May 8, 2015 Share Posted May 8, 2015 Mike, In reading your post again I think you better pull your thermostat and take a look at it. They sit low on the LS motors and are prone to accumulating debris out of the radiator. A thermostat stuck partly open would explain your symptoms. I had that happen to me when I had a leak repaired in my radiator. Evidently some solder came loose and ended up in my thermostat. I replaced it but when I later took it apart to check it out I found the solder wedged into it. Quote Link to comment Share on other sites More sharing options...
mistafosta Posted May 11, 2015 Share Posted May 11, 2015 Mike, In reading your post again I think you better pull your thermostat and take a look at it. They sit low on the LS motors and are prone to accumulating debris out of the radiator. A thermostat stuck partly open would explain your symptoms. I had that happen to me when I had a leak repaired in my radiator. Evidently some solder came loose and ended up in my thermostat. I replaced it but when I later took it apart to check it out I found the solder wedged into it. Also check the airbleed setup. Do you have them blocked off, or routed so they allow air out of the engine? Pretty sure a cowl hood is not going to cause issues like that. Quote Link to comment Share on other sites More sharing options...
MrPhotographer06 Posted May 13, 2015 Share Posted May 13, 2015 I agree, a cowl hood shouldn't cause these issues. Is your cooling system fully burped? Quote Link to comment Share on other sites More sharing options...
Zfan1 Posted May 13, 2015 Author Share Posted May 13, 2015 (edited) Yes it is, new Griffith Radiator, Lincoln 2 speed fan. She runs nice and cool around town, never above 195, but get on the highway and after 15 minutes of driving the temp keeps creeping upwards to 210-215. When I get back off the highway she drop back down to 180-190. I got to thinking about how the cowl works and what it's original purpose was for. It was to be sealed around the air cleaner delivering cold air to the carb not the engine bay. If the engine bay is open to the high pressure wouldn't that cause some turbulence with the air being sucked thru the radiator, kind of like a back pressure at higher speeds? Anyway, I put the louvered stock hood back on it so we shall see how she runs in a few days, I am curious to say the least. Edited May 13, 2015 by Zfan1 Quote Link to comment Share on other sites More sharing options...
mistafosta Posted May 13, 2015 Share Posted May 13, 2015 Yes it is, new Griffith Radiator, Lincoln 2 speed fan. She runs nice and cool around town, never above 195, but get on the highway and after 15 minutes of driving the temp keeps creeping upwards to 210-215. When I get back off the highway she drop back down to 180-190. I got to thinking about how the cowl works and what it's original purpose was for. It was to be sealed around the air cleaner delivering cold air to the carb not the engine bay. If the engine bay is open to the high pressure wouldn't that cause some turbulence with the air being sucked thru the radiator, kind of like a back pressure at higher speeds? Anyway, I put the louvered stock hood back on it so we shall see how she runs in a few days, I am curious to say the least. The louvers will be better probably, but normally the cowl area is completely closed, so the cowl hood is no worse than stock. And at idle it allows as much air to flow out as the vents would. As for the high pressure area, I've read a lot of studies on it and the consensus is that at speed it is similar to stock hood airflow. How is your cooling system setup? I chased a ton of gremlins thinking airflow was my cooling system issue (Same as yours, heating at higher speed) and it was actually the cooling system routing. At street level of use its almost never passive airflow. Quote Link to comment Share on other sites More sharing options...
texis30O Posted May 15, 2015 Share Posted May 15, 2015 With my blower I am seeing 180-190 at freeway and stop and go traffic conditions. I have a factory hood on it now but also have a low rise cowl that I have hanging in the garage. I added vents in the hood to assist with cooling, but all of this is no good to judge till I get all of my front end boxed in to control the air flow . Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted May 15, 2015 Share Posted May 15, 2015 Ive been told that the LS family runs best hot. I think the high speed fan comes on at 229 degrees. Mine typically runs 205-210 degrees and seems fine. Quote Link to comment Share on other sites More sharing options...
heavy85 Posted May 15, 2015 Share Posted May 15, 2015 I got to thinking about how the cowl works and what it's original purpose was for. It was to be sealed around the air cleaner delivering cold air to the carb not the engine bay. If the engine bay is open to the high pressure wouldn't that cause some turbulence with the air being sucked thru the radiator, kind of like a back pressure at higher speeds? That Im guessing is your problem. I ran the stock 240Z radiator for several years and only had cooling issues at slow speeds where the fan couldnt keep up but always rock steady at the stat setting on the highway. Hell I ran a year without a fan at all after the Spal blew up. Controlling airflow is critical. For example adding the front splitter hurt temps but sure helped lap times. Quote Link to comment Share on other sites More sharing options...
zdlite Posted May 15, 2015 Share Posted May 15, 2015 Early Z cars has issues with under car turbulence slowing airflow through the radiator at speed. Datsun started installing chin pans as a fix, a pan that bolts on just under and behind the radiator. I guess it is possible that a cowl hood could disrupt under hood air flow patterns. None the less a chin pan might not be a bad idea. Quote Link to comment Share on other sites More sharing options...
The Infidel Posted May 16, 2015 Share Posted May 16, 2015 240z are hen's teeth. 280z verisons are around, I have a clean one collecting dust if interested. Quote Link to comment Share on other sites More sharing options...
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