Hello Everyone!!

I've searched the forum and I can't find a solution to my problem.

Here's the deal:

I replaced my 150,000+ mile engine with one that's barely over 50K mi., and it's overheating while driving at highway/freeway/motorway speeds. During idle, and while running errands, it doesn't overheat, but once I hit 50mph sustained for a while, the temp gauge just keeps creeping up and never cools back.

1. No thermostat is installed, in Puerto Rico temps rarely lower from 80F.
2. The water pump is brand new.
3. No coolant is leaking, and the cooling system holds pressure well.
4. The radiator (2 row) is new (recored), and after the engine was installed, it's been flushed TWICE to remove all the junk left over from the engine re-build. PLUS, it's been rodded, just to make sure.
5. Plenty of water and coolant...

I'm running out of options, aside from installing a 3 row core. Engine compression is good, and I doubt the heads are leaking, since the coolant doesn't go anywhere, except when it boils over.

The radiator cap is NOT OEM, I'll be looking for an OEM soon, just to be sure.

PLEASE help meeeeee...I'm out of my wits with this one. <img src="/forums/images/graemlins/scared.gif" alt="" />

Thanx!!

First you need to install a thermostat, which has nothing to do with how hot or cold it is where you live <img src="/forums/images/graemlins/cheers.gif" alt="" />
You will also get better gas milage with the thermostat installed.

Since your overheating at speeds above 50mph, I suspect a few things. Since you have lots of air flowing at 50mph you should not overheat. I suspect you have a clogged catalytic coverter, crushed exhaust pipe or some type of exhaust restriction. Second, you might also be running lean because of the missing thermostat, running lean causes excessive engine heat.

My final thought is your fan clutch could be bad. Since you don't have a thermostat it will take a long time for your engine to warm up. After your engine is warmed up, have a friend turn the truck off while you watch the fan. It should stop almost right away. If it continues to spin then it's bad.

<img src="/forums/images/graemlins/cheers.gif" alt="" />

Thanx for replying!!

1. Exhaust is not crushed or restricted. The Cat Conv. might be contribuiting, will schedule a replacement.
2. The thermostat goes in tomorrow, a lean mixture might be the reason.
3. Fan clutch will be the next item to replace, it rotates about a 1/4 turn after the warm engine is turned off. I hope I can find one locally for a decent price.

Thanks again!!

I would not be surprised if the installation of the thermostat cures the overheating. When there is no thermostat it's possible the free flow of coolant does not stay long enough in the rad to cool enough.

My '92 3.0 did the exact same thing. Replacing the fan clutch resolved the issue for me. However, my old fan would rotate MUCH more than yours when I turned the engine off...it was completely worn out.

UPDATE:

Well, I replaced the fan clutch, and installed the thermostat. I took her out for a 45min ride at highway speeds (34 to 70mph) sustained for about 30min. The temp gauge did not move from slightly above normal. Granted that it was 78F when I tried at 5am, but apparently it's not overheating. Since it's summer, I'll try doing a longer run at 100+F heat and post another update.