I have a 95 4runner with a 98 4.3 vortec engine still stock . Im running the 3.0 radiator.Now im trying to get a 180* thermostat in it and once I let it sit and idle it will run about 180* but when I start driving it it acts like it full of air and I cant get it out. I have had to put the 160* thermostat back in it and it has no problems other than not wanting to get up to temp now . Can someone pleast tell me how to overcome this problem and I have tryed 2 diffrent thermostats in it and both had done the same thing I even thought it may be the gauge and started running duel gages so that I could check to see if it was the gauge or not. This had drove me crazy please help.

 

Are you running the EFI or did you swap to a carb?

I thought those engines were designed to run with a 210* thermostat with the ECU and EFI.

 

I did the carb swap planning on running propane

 

There's your problem. You put a chevy motor in a toyota. and now the japanese Gods of lackinginhorsepower are smiting you!

 

Is the water pump new or old? might have some broken vanes barely circulating water at idle. Also your radiator cap has to be at least level with the highest point of the coolant system to include the heater core. If your cap is lower you will have to put an air bleeder at the highest point in the system to get all the air out. Im runnin a 500hp V8 and i ran into the same problem. I moved my radiator up to just past the top of the core support. Problem solved, now my rig runs at 180* no matter what im doin. Hope this helps out.

 

The waterpump was on a stroker motor that we had at the garage. I pulled the pupmp off of it and put on the 4.3. While its its at a idle it it will stay at the temp that it suppose to be at but when im going down the road is when it acts crazy. I was thinking maybe that the waterpump was causing the problem also. But i was wanting to get other suggestions on what could cause the problems.

 

Ok what about standard vs. reverse rotation water pumps. I know gm used both in the 4.3 time frame. I know LT1's used reverse flow but others used reverse rotation standard flow. The water pump may need to spin the other way in order to work. it all depends on your belt drive setup. You have a 383 pump which is more than likely a conventional rotation pump. If your water pump has a smooth pulley vs. a grooved one it is supposed to turn opposite of the crank shaft. The 383 pump is supposed to turn with the crank. Post up pictures if you want and i can tell you for sure what pump your supposed to have.