Car over heating very fast under load...

[96Holly]

'96 LT4. I installed a Mez. elec water pump last year. (no problems up to this point.) I just replaced all three relays (they tell me the 4 prong relays are no longer made?) and replaced the main fan moter and repled a blown fan fuse. (I am assuming the fuse blew when the fan motor blew...)

Once all was installed, filled with coolent and bubbles purged (I think) and stared, all was well. Fans came on at right temp and also came on with the A/C on. It cycled through the 229 fans on and off at the lower temp with no issues.

I got it on the road yesterday and wham... about 1.5 miles down the road my analog temp gage was pegged and my degital was on the way up. I didn't bother checking the gages being so close to home and started out with a cold engine. I got it home with bubbles churning from the overflow tank and both gages way to hot... (unfortionatly it ran for about 5 minutes or less with my check gages light on)

I plan on hard wiring the fans and water pump and run it down the road to see if something isn't correct there.

Why would it only overheat under load and not at idle? Any ideas/comments would be approciated.

 

[96Holly]

Sorry, I replaced all three fan relays.

 

[Radar]

Did you check the pump motor rotation direction? With all of that rewiring work, you might of reversed the polarity on the pump motor. A DC motor will run in reverse if the terminals are backward. It's a long shot but worth checking.

Anyway, a centrifugal pump running backward will pump water, but the volume is way down. So maybe at idle, there is enough flow, but at load, the engine overheats.

I would also recheck for air in the system.

Radar

 

[96Holly]

System bugged me out....

Thanks Radar...

I ran the car for about 2 mo last season and a couple of times this season. The problem "came on quick." I almost want to say that it's a mechanical problem like the impeller coming loose on the pump shaft or a head gasket or ??? If the hard wiring test fails I will look into that further.

I also cleaned out the rad when the pump was inslalled (actually removed it and cleaned the fins). I couldn't see any debris on the front side.

Other information: After I installed all my shinny new parts, I filled the system with the air bleed screw open (screw not off) and the small right hand side tube on the rad loosened. I started the car to purge any other air bubbles. At the filler tank the system purged and gushed water over the top when it reached past 190. I shut it down, filled it again, capped it ran it then shut it down and really loosened the screw and small hose attachement at the rad. Got a steady steam from the screw, some fluid at the small tube so I tighten all let idle to watch the fans kick in at the appropriate times.

 

[Radar]

Boy, really sounds like you hit all of the bases.

I still would look for air binding. Can you tell if there is coolant flow into the radiator when the engine is hot? That would tell you if the pump has a broken impeller, would it not? Sure sounds like a gross lack of water flow or air binding to me. I know that a bad head gasket can cause some overheating but you would see a lot of exhaust gas escaping from inside the radiator as well as coolant in your oil pan.

Just wondering why you removed the stock engine driven water pump?

Radar

 

[96Holly]

I actually moved this to the Technical and perf mods list.

I didn't get any exhaust gas when it was bubbling over when I was purging. I agree that it sounds like a major flow problem.... therm stat.... pump.... I don't think it could be a pluged rad given the fact that it ran so good last seasons and earlier this year.

vettelt193 gave me a good idea to remove the stat, hard wire the pump and run till hot (above 200). Cut it off then keep the pump going to see if the temp drops fast or slow. This could be a good indication that it's the pump (slow temp drop) or a bad stat (fast temp drop)

I installed the electric pump mainly to get out of the dang weap hole. I figure the pump will last just as long as a replacement. Car is not a daily driver. I guess I could feel a difference in HP but the jury really is out on that one. It was fun to install though.

 

[96Holly]

Oh ya... thanks for your reply

 

[grapeknutz]

I really think that the radiator internally is plugged up. If you have over 60000 miles think about getting a new radiator, I know mine up plugged up at that miles. Also use distilled water with the anti freeze!

 

[96Holly]

Thanks.... Question....

I really think that the radiator internally is plugged up. If you have over 60000 miles think about getting a new radiator, I know mine up plugged up at that miles. Also use distilled water with the anti freeze!

The problem came up very fast like almost instant. Driving along one day at normel temps then the next day wham boil over in a very short amount of time. My thought is that a pluged Rad would deteriate over time. Although I will not disregard (Sp?) it, I will consider it after my removal of the stat.

Thanks again.

 

[grapeknutz]

Mine happened on a HOT July day, it got hot fast!