kiwican Posted September 20, 2021 Report Share Posted September 20, 2021 I have done a lot searching on this but have not come across my exact situation. I have a Tr8 with a 3.9 motor and aluminum radiator. It overheats after about 20 miles of freeway driving, we usually drive about 70 mph. It does not seem to overheat on surface streets although it maybe that we just dont drive long enough at the slower speeds to get there. By overheating I mean it will be pumping coolant out of the overflow from the expansion tank. I have changed the radiator cap and the thermostat (180 deg F) is operating correctly. The level in the expansion when cold is about half. I did a test on the coolant and there does not appear to be any exhaust gas in the coolant. Oil shows no sign of water. I guess next step is to get the radiator checked / cleaned but any other suggestions would be appreciated Thanks. Simon Quote Link to post Share on other sites
john.r.davies Posted September 20, 2021 Report Share Posted September 20, 2021 That you get overheating at high speed suggests an aero reason. Something is inhibiting rad air flow in that situation. Anything in front that wasn't originally? Badge bars, relocated number plate? John Quote Link to post Share on other sites
MadMarx Posted September 20, 2021 Report Share Posted September 20, 2021 clogged radiator or blown headgasket Quote Link to post Share on other sites
kiwican Posted September 20, 2021 Author Report Share Posted September 20, 2021 Hi John, There is nothing new been added to block air flow. Hi Christian, I am going to get the radiator flushed and checked along with a new water pump. If that does not solve it then I guess it is head off time. There is no indication of water in oil and a test of the coolant showed no signs of exhaust gases present but that will be last thing I guess. Thanks for the replies Simon Quote Link to post Share on other sites
BlueTR3A-5EKT Posted September 21, 2021 Report Share Posted September 21, 2021 12 hours ago, MadMarx said: clogged radiator or blown headgasket +1 Quote Link to post Share on other sites
Adrianmil4126 Posted September 21, 2021 Report Share Posted September 21, 2021 Hi Simon I had the same issue . It was the head gasket; water leaking into the cylinder and then out through exhaust (it was between the back 2 cylinders on one bank). It did not show on compression test when car engine cool. It happens at motorway speed because there is more ‘pumping’ pressure and engine hotter than at lower speed. Regards Adrian Quote Link to post Share on other sites
BusheyTrader Posted September 21, 2021 Report Share Posted September 21, 2021 (edited) I had the same issue with mine. A 30 year old V8 radiator with cold spots at the bottom indicating it was clogged / furred up in places. I used every commercial flushing agent, including white vinegar, they didn’t help. I could have had the radiator recorded or Rodded but it was more cost efficient to have a new aluminium rad. The coolant was regularly replaced and never run without inhibitor / antifreeze in it. A change to a new radiator and at 70mph now the gauge barely moves above where the thermostat opens, even in this summer’s 35C. Head gasket, ignition timing that’s way off or a silted up radiator or a combination of all three are my suggestions. Buy a cheap infrared temperature sensor, run your engine up until the thermostat opens, then measure the temp in various places. The clogged rows, usually the bottom ones will be cooler if they’ve silted up and set solid. Edited September 21, 2021 by BusheyTrader Quote Link to post Share on other sites
kiwican Posted September 21, 2021 Author Report Share Posted September 21, 2021 (edited) Thanks for the replies everyone. I am going to get the radiator removed and properly tested and cleaned. I am now wondering if I might as well just bite the bullet and have the heads pulled and the same time and then there will be no doubt. Regards Simon Edited September 21, 2021 by kiwican Quote Link to post Share on other sites
kiwican Posted January 25, 2023 Author Report Share Posted January 25, 2023 Resurrecting this thread, the issue was a blown head gasket. That has been repaired and car is running well. I do have a couple of additional questions. What is the normal operating temperature of a TR8 with the 3.9 motor? I have read the normal T/stat is 195 so I assume it is 195 or a bit higher. What would be the max normal temperature? I have installed a digital temperature gauge with the sending unit where the sending unit would be to operate the radiator fans when AC is fitted. I dont have AC fitted. On the freeway the digital gauge will head to 200 at which stage I chicken and turn on the electric fan, which will drop the temp to 185 ish. I feel like at highway speeds the temperature should be controlled just by airflow through radiator. I have not let it the temperature rise to see if it stabilize. Am I being too paranoid or is the car running hotter than it should? Putting an IR thermometer on the radiator shows the coolant going into the engine at 160 ish. I need to check as it has been awhile since I did that. Thanks Simon Quote Link to post Share on other sites
BusheyTrader Posted January 26, 2023 Report Share Posted January 26, 2023 (edited) Hi Simon, Carburettor RV8’s in the UK are often fitted with 82c / 180F thermostats and for efi 88c / 190F. At motorway speeds of around 70 mph, my carb’d V8’s temperature gauge sits just above the thermostat opening point in cool to warm weather and a touch more at 35c, with a relatively new TR8 aluminium radiator. If you have the higher temperature stat fitted you may well be ok. If not, did you have your radiator checked out as per your post? Edited January 26, 2023 by BusheyTrader Extra text Quote Link to post Share on other sites
kiwican Posted January 26, 2023 Author Report Share Posted January 26, 2023 2 hours ago, BusheyTrader said: Hi Simon, Carburettor RV8’s in the UK are often fitted with 82c / 180F thermostats and for efi 88c / 190F. At motorway speeds of around 70 mph, my carb’d V8’s temperature gauge sits just above the thermostat opening point in cool to warm weather and a touch more at 35c, with a relatively new TR8 aluminium radiator. If you have the higher temperature stat fitted you may well be ok. If not, did you have your radiator checked out as per your post? I have a 160 deg (70c)T'stat fitted. I will double check about the radiator. I imagine it is OK as when the fan is running it drop the temperatures quite quickly, but without the fan the temps continue to rise. That makes me think there is an air flow issue as at 70 mph it should be getting more than enough air flow to not need the fan. If it is air flow I dont know the solution would be. Quote Link to post Share on other sites
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