To preface my temp gauge never goes above 1/2 way and my fluid level is consistent so I am not overheating as far as I can tell.

I've been fighting an intermittent problem for months now where the car will run amazing for a few days and then all of the sudden the car starts to run like it is missing a cylinder. This happened again on the way home last night. I started the car today and it ran great for about 2 mins and then started missing.

Guessing that the problem is worse at operating temp I checked the radiator hoses and noticed that there really isn't any pressure in any of the 2 hoses and the lower hose is 10x cooler than the top hose. The top hose is hot to the touch, where the lower one I could hold all day without an issue. I am guessing that can't be right.

Is there anything in the coolant system that could cause a car to run great for a week, then 'drop a cylinder' another day and then the next day be back to normal for a few days?

Currently the car shows no codes, even when running horrible

Other ideas?

I have already done
cap, rotor, plugs, compression test all good. tuneup set to 10 degrees
replaced all air lines, pcv valve, and checked for leaks.
cleaned maf sensor
sent ecu to tanin for repair
checked electrical and battery is 12.2v idle and 13.6 running so alternator is ok.
checked every single electrical connector under the hood to make sure not brittle and connected properly.

 

forgot to ask, Are the radiators for the manual supra and sc300 the same?
Would rather not have to go to the dealer for a radiator if I can find a great aftermarket one.

 

This should be normal. It means that your radiator and fan is doing their job well of cooling the coolant.

Hot coolant from engine goes in the radiator through the top hose.. so that should be hot. Then radiator with your fan cools the coolant so what comes out of radiator through lower hose towards your engine should be cooler.

The other problems of your car running good and the next week erratic can be caused by a lot of things.

 

Thanks for info.

Yeah, I am totally grasping at straws trying to figure out the running issues. I was only assuming something might be wrong because the last time I messed with radiators was a classic mustang where both hoses were always at least very warm to the touch. The sc lower hose is actually cool, zero added temp. Also the wall thickness of the tubes felt rather thin without a lot of pressure. I just expected more pressure I guess. Glad to hear it is normal though. Off to think of other possible causes.