Quote:The stock pulleys are fine at sustained 5,000 rpm driving (with A12 engine). Is the A15 water pump and pulleys different?

At speed is the problem then. . .

OK, make sure that the water pump is not spinning too fast, it will cavitate(not pump). Put as big a pulley on it as possible, Was it swapped at the time of the engine swap? (people do strange things to avoid buying a longer belt!) Is the pump OK?

The other thing that will push it over the edge is not enough advance in the dizzy. Try advancing it, say 10 degrees, gently bing it up to speed (avoid detonation), See if this makes a difference!

It could also be running a touch lean or the cam could be a little too retarded (use an early cam gear to advance it). Id check the first 2 though for starters.

I had the same problem in my F100 when ever i was towing a car on the highway. It only got hot when it was held fairly flat to the floor but then i would back off and it would cool down. I found that it was a fuel problem when the carby was held wide open for a long period of time. It won't do it around town because of the different amounts of fuel at diferenent revs, but on the highway held flat it is constant. Can't remember if it was leaning out or too rich. It might help you anyway

Just my thoughts.
Jason

Quote:This does not indicate overheating.

If you really want to know, without spending more dollars ...
1. measure the actual temp at which thermostat opens (and how far it opens) by using a boiling pot and a cooking thermometer, as noted in the Nissan manual
2. Measure the actual temp in the radiator using a thermometer (start it up with cap off, let it idle till it's fully warm)

BTW, this a15 motor,
was it reconditioned.
Did you have the head re-torqued,
are the water hoses inserted properly without major bends,
did you try using some coolant in the radiator, have you flushed the radiator,
remember timing can also cause o\heating?
If all these are fine, I'd check the head and gasket for sure.

I dont think theres any problem with the guages on the inside.

These problems you experiencing at present is also experienced by GXMAN.

i had the same problem on my old ute. had an A15 and gemini radiator but was still getting hot. i tried everything, replaced waterpump, thermostat, flushed radiator professionally, flushed block, took head of and got it resurfaced and pressure tested, checked for rags left in the block or maybe a bee hive while i was there, once cooling system was all connected, replaced radiator cap, replaced temp guage, replaced temp sender, replaced hoses, moved mechanical fan closer to the radiator, coupled that with a thermo fan and nothing!!! it was still running hot. in frustration i took it to a mechanic and got him to look at it, he had no idea either... well actually he said he fixed it and charged me like $400 but it still overheated over and over again. then all of a sudden one day it just stopped overheating. I was like.. what the?? and yeah i still have no idea what it was to this day. soon after it stopped overheating i sold it but i dunno if it ever came back for the next owner. i hear that once a car is hot the hoses can colapse if they are old. try this as it seems to be the biggest "mystery" cause of overheating if youve tried everything.

thats what i thought that the head gasket was on its way out!!. The thermostat is the right rating!!! Say im drivin around town, it sits between the cool and middle, but then as soon as i get on sum open road it goes up 2 between middle and hot!!! Um i tried idling the engine 4 15mins and it was pretty good and didnt really move from between cool and middle. Its got me confused!! Do u think its the head gasket???, by the sounds of what i have explained

Have you tried idling the motor for a long time whilst parked.
Does it heat up?

Does she heat once you press on it on the open road, however, if you take off your foot of the pedal and let her coast, does she start cooling down.

If this above is happening and you say alls fine with cooling system {radiator, fans, pipes, t\stat], then I assume that your h\gasket is on the way out.

At what temp does the thermostat open and does this match it's rating? What is it's rating?

hey, ok heres my problem:
I recently got a a15 put in!!!. The temperature sender was apparently stuffed so i replaced that with my old a12 sender!!.I know this sender was workin fine, as it was on my old engine and read correct. When i drive with my foot flat on the highway it seems 2 be getting hot!!!. I have checked the thermo stat, which is opening!. I have a redone 1500 radiator with an electronic fan and engine fan going and that is all fine!!!
Now this is where im confused, could it be that my temp guage is not reading correct on the dash ,or the a12 temp sender is diffrent from the a15. Or is it somethin a lil more serious. When i say its gettin hot i mean like its sittin between halfway and the hot marker. It shouldnt be doin that in this weather i would have thought cause it isnt very hot down here!!!. Any help or input in 2 this problem would be much appreciated!!!