workingdog
GOLD Star
I've been posting a lot of questions lately, since I just took delivery of my '84 FJ60 from Valley Hybrids 2 weeks ago, so I thought I post a solution I found to an overheating problem with the 2005 5.3l Georg installed.
The FJ60 had run like a top, except for a small wiring problem, until a couple of days ago, when it began to go into limp mode due to overheating. This problem was complicated by the fact that the temp gauge wasn't working so it took a scan gauge to figure out what was happening. The temp was wandering between 220 and 269 when it would go into limp mode. Georg suspected the temp sensor, so I replaced that but the problem only got worse and I was now noticing a lot of coolant leaking from the rear seat heater - but not enough that I couldn't keep ahead of it by keeping the expansion tank full.
I bypassed the rear seat heater and filled everything back up, but the truck was now overheating in less than two miles with full radiator and full expansion tank. I had purchased and was about to install a new thermostat when I did some searching on Google. Based on what I found, I pulled off the top radiator hose and stuffed the hose down it. It ran for quite a while, much longer than required to fill the house. I hooked it back up and my problem was mostly solved.
The thing it took me a while to figure out is that these cooling systems are backwards from old school SBCs. The thermostat is on the bottom hose and the water pump has to have enough water in the block to prime it - no matter who much water is in the radiator and expansion tank.
Here's what I think happened. All this occurred when I started to use the heaters. I think there was air in the primary heater coil that got into the system and the bad rear seat heater core allowed more air into the system. Just enough for the water pump to go dry and not be able to prime itself. Full radiator, full expansion tank, but with an unprimed pump, no coolant is moving and the truck heats up almost immediately.
I'm still going to replace the thermostat, because the truck is running steadily between 215 and 230 - which is a little higher than I'd like. I'm also going to install one of those flush T's into the upper radiator line that will allow me to fill the radiator from the top of the upper hose.
Peter
The FJ60 had run like a top, except for a small wiring problem, until a couple of days ago, when it began to go into limp mode due to overheating. This problem was complicated by the fact that the temp gauge wasn't working so it took a scan gauge to figure out what was happening. The temp was wandering between 220 and 269 when it would go into limp mode. Georg suspected the temp sensor, so I replaced that but the problem only got worse and I was now noticing a lot of coolant leaking from the rear seat heater - but not enough that I couldn't keep ahead of it by keeping the expansion tank full.
I bypassed the rear seat heater and filled everything back up, but the truck was now overheating in less than two miles with full radiator and full expansion tank. I had purchased and was about to install a new thermostat when I did some searching on Google. Based on what I found, I pulled off the top radiator hose and stuffed the hose down it. It ran for quite a while, much longer than required to fill the house. I hooked it back up and my problem was mostly solved.
The thing it took me a while to figure out is that these cooling systems are backwards from old school SBCs. The thermostat is on the bottom hose and the water pump has to have enough water in the block to prime it - no matter who much water is in the radiator and expansion tank.
Here's what I think happened. All this occurred when I started to use the heaters. I think there was air in the primary heater coil that got into the system and the bad rear seat heater core allowed more air into the system. Just enough for the water pump to go dry and not be able to prime itself. Full radiator, full expansion tank, but with an unprimed pump, no coolant is moving and the truck heats up almost immediately.
I'm still going to replace the thermostat, because the truck is running steadily between 215 and 230 - which is a little higher than I'd like. I'm also going to install one of those flush T's into the upper radiator line that will allow me to fill the radiator from the top of the upper hose.
Peter