Guest HALLOWEEN Z Posted December 24, 2009 Share Posted December 24, 2009 I've had problems with temperature fluctuations and I think it stems from my car overheating back a long time ago. That was the same day my tranny broke. I drove it back in reverse and forgot to turn the fan on. It's been a while, itseems like it may have done it before but I'm not sure. my cars a 280z with a 350. has vortech heads and an aftermarket cam. Anyways...as soon as my car gets to 180 degrees it will move up to around 220 and then cruise back down. i only notice this on the highighway. If I let off the throttle or blip it it will quickly drop back down to 180 also. If I do nothing then the temp will take off or drop back down. I'm pretty sure I'm getting all the air out of the coolant system it's the only time i've had this type of problem I let it warm up with the cap off and have someone hold the throttle while I top off the water. hears what else i've done changed the thermostat to eliminate that possibility, did nothing hoses don't seem to be collapsing that I can tell no white smoke exitting exhaust oil looks good water looks normal I did a compression test. i have 2 more hard to get cylinders left. I have to take headers off for them. The engine was cold however so I may have to redue the bad cylinder after I let it warm up. It's cold in texas today. anyways cylinders testing at 160 with throttle open. I've got one that tested at 110 with throttle opened. also! When I fill the radiator with water...if I let it run for about 10 seconds...way before thermostat opens...the engine slowly pushes water out. it's very slowly just kinda trickles out where the radiator cap is off. and...if I put radiator cap on and let it run for a few seconds and remove cap theres a little pressure I hear released when I take off cap. could I have a blown headgasket or cracked head and maybe it's just small so It's kinda pressurizing the coolant system? I can't think of anything else to try. oh and the fan isn't blowing backwards. and it hasn't always done this with the temperature fluctuating so I don't think it's an airpocket from the front end of the car. thanks, nathan Quote Link to comment Share on other sites More sharing options...
hoov100 Posted December 24, 2009 Share Posted December 24, 2009 I've had problems with temperature fluctuations and I think it stems from my car overheating back a long time ago. That was the same day my tranny broke. I drove it back in reverse and forgot to turn the fan on. It's been a while, itseems like it may have done it before but I'm not sure. my cars a 280z with a 350. has vortech heads and an aftermarket cam. Anyways...as soon as my car gets to 180 degrees it will move up to around 220 and then cruise back down. i only notice this on the highighway. If I let off the throttle or blip it it will quickly drop back down to 180 also. If I do nothing then the temp will take off or drop back down. I'm pretty sure I'm getting all the air out of the coolant system it's the only time i've had this type of problem I let it warm up with the cap off and have someone hold the throttle while I top off the water. hears what else i've done changed the thermostat to eliminate that possibility, did nothing hoses don't seem to be collapsing that I can tell no white smoke exitting exhaust oil looks good water looks normal I did a compression test. i have 2 more hard to get cylinders left. I have to take headers off for them. The engine was cold however so I may have to redue the bad cylinder after I let it warm up. It's cold in texas today. anyways cylinders testing at 160 with throttle open. I've got one that tested at 110 with throttle opened. also! When I fill the radiator with water...if I let it run for about 10 seconds...way before thermostat opens...the engine slowly pushes water out. it's very slowly just kinda trickles out where the radiator cap is off. and...if I put radiator cap on and let it run for a few seconds and remove cap theres a little pressure I hear released when I take off cap. could I have a blown headgasket or cracked head and maybe it's just small so It's kinda pressurizing the coolant system? I can't think of anything else to try. oh and the fan isn't blowing backwards. and it hasn't always done this with the temperature fluctuating so I don't think it's an airpocket from the front end of the car. thanks, nathan Did you purge the cooling system of air? Quote Link to comment Share on other sites More sharing options...
Guest HALLOWEEN Z Posted December 24, 2009 Share Posted December 24, 2009 I like your 2nd ammendment quote...I had the thermostat off when I filled with water. what exactly do you mean by purging it though? I've never had this kind of problem before on any other vehicle. Quote Link to comment Share on other sites More sharing options...
Guest HALLOWEEN Z Posted December 24, 2009 Share Posted December 24, 2009 by the way i have no overflow canister...I don't think it's necessary is it? Just tryin to give as much info as possible Quote Link to comment Share on other sites More sharing options...
hoov100 Posted December 24, 2009 Share Posted December 24, 2009 guess i should have worded it different, i meant to ask, did you bleed the system? Quote Link to comment Share on other sites More sharing options...
MikeJTR Posted December 24, 2009 Share Posted December 24, 2009 I think the temperature fluctuations you are seeing are somewhat normal, but there is a way to reduce it. You engine has an outlet sensing thermostat. What this means is that the coolant gets heated up in the engine, and eventually, the coolant gets to the thermostat, at which point it opens. In your case, the engine in the coolant (where your temperature sensor is located) gets to 220 before the coolant to the thermostat gets to 180. After the thermostat opens, cold coolant from the radiator circulates through the engine, and when it gets to the thermostat, the thermostat closes. This cycle will continue for a few cycles, but it typically stabilizes after a few minutes, and you will see a steady temperature. More modern engines, such as the LT1 and the LSx engines use an inlet sensing thermostat that mixes coolant from the engine and the radiator. The inlet sensing thermostats prevent the spikes in temperature that you are seeing on your car. On your car, drilling a couple of small holes in the thermostat will allow a small amount of coolant to constantly flow through the thermostat, and this will prevent the temperture spikes that you are seeing. If the holes are small enough, you will barely notice an increase in the time it takes for the thermostat to open. Another solution is to run a bypass hose from the thermostat to the lower radiator hose. One more note, I have seen this problem when more than 50 percent anti-freeze is used, so if it continues, check the percentage of antifreeze in the coolant. A measuring tool for this is usually available at auto parts stores for about $15. Quote Link to comment Share on other sites More sharing options...
Guest HALLOWEEN Z Posted December 25, 2009 Share Posted December 25, 2009 right now I have the sensor up by the thermostat. I had it on the head but got burned by the block huggers once and I moved it. I was thinking it over today and had a thought that when all this happened to the car and it overheated I also lost the overflow because it got stepped on in the garage. I know it's not usually necessary to have one but...but i was thinkin that when the water gets hot ofcourse it expands and an overflow will allow this and will let it back in when it cools. without an overflow you always get an airpocket atleast until it gets hot. but the top of my radiator is at the top of my thermostat...about level radiator maybe a little higher. I wander if that could cause the problem to. Even if I get this solved I need to see why i've got low compression in one cylinder. I'm going to try it again hot. Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted December 25, 2009 Share Posted December 25, 2009 read thru this http://forum.grumpysperformance.com/viewtopic.php?f=57&t=348 Quote Link to comment Share on other sites More sharing options...
Guest HALLOWEEN Z Posted December 26, 2009 Share Posted December 26, 2009 thanks for the info. I'm going to take a good look at it today and I'll let you know how it goes. I've always wondered what the optimum range is for engine temperature. Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted December 26, 2009 Share Posted December 26, 2009 fOR A STREET CAR ENGINE THATS EXPECTED TO LAST FOR THOUSANDS OF MILES AND GO A LONG WAY BETWEEN TUNE-UPS,Ive always found that keeping THE AIR AS COOL AS i CAN GET IT the coolant temp at 190f-200f, AND THE OIL AT 200f-220f WAS A VERY USEFUL RANGE FOR PREDICTABLE POWER AND EASE OF TUNING Quote Link to comment Share on other sites More sharing options...
Guest HALLOWEEN Z Posted December 26, 2009 Share Posted December 26, 2009 ya I think I was pretty much worried about NOTHING. I drilled two holes in the thermostat and installed an overflow canister...now it's warming up and staying on 170 and up to 180 sitting still. I've got a 180 thermostat so maybe I should go up to a 190 atleast. Also tested the cylinder that showed low in the compression test after I warmed the car up and it's also on 160 so no worries Quote Link to comment Share on other sites More sharing options...
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