Litermonster

First off, I have a 1990 2WD Toyota pick-up. I have recently installed a brand new radiator, radiator cap, water pump, thermostat, and fan clutch. It turns out that the Fan clutch ended up being the culprit. Well, 3 days after i replaced the fan clutch, the yota started overheating again on the interstate....anything over 55 to 60mph. It also would overheat when at idle. So I thought I would replace the fan all together with an electric unit.

I had a giant electric fan laying around that was taken off of an Ford Excursion. So I proceeded to fab up and install this fan, (its rather large, takes up the whole surface area of the radiator). I get the fan working, and the yota no longer overheats at idle, the gauge just barely comes off the "C".
The first interstate test upsets me, as the truck still overheats at faster speeds.

I am thoroughly confused at this point. I was thinking that maybe the carb needed adjustment. Maybe it does fine at idle but leans out when at a higher speed on the interstate causing the overheating?

91Toyota

Hmmm...is it "actually" overheating?

Litermonster

If you consider spraying out the over-flow overheating?

91Toyota

Spraying out the over-flow? No clue what your talking about. Did you burp the cooling system? It could be the thermostat...even though its new. Heck, I bought 3 thermostats and they all didn't work. I drilled a hole in one and haven't had a problem since. Try it w/o a t-stat...and see what happens

Litermonster

Well I am very sure of myself when I say its overheating

Never burped the system, what does that consist of?

91Toyota

Leaving the radiator cap off (while parked on an incline!) and waiting till the t-stat opens then it burps itself (antifreeze comes out) Maybe I'm wrong though...you should probably get a couple more opinions before trying what I said

Litermonster

Thank you for your advice.

ovrrdrive

Don't run it without a tstat. It can actually cause your engine to either sludge up or possibly even overheat. It's there for a reason and if everything is working properly your truck won't overheat with it in.

Are you sure you got the right pressure cap?

Does the temp gauge show hot when it starts boiling out the overflow?

If it ran hot before, are you sure you didn't overheat it and blow a headgasket?

Are you sure the tstat isn't in backwards?

All you need to do when you have had the cooling system open is to fill it up, run it with the cap off until the tstat opens up and the water level drops, and then fill it as full as you can. I usually rev it up so the water level drops down and hold the revs until I top it off and then cap it.

Litermonster

Well, it heats up, I pull over, and it is boiling over....

I installed the t-stat correctly, and I have checked for signs of a blown head gasket. No water in the oil.

The darn thing runs perfectly at idle in 110 degree weather for 20 minutes, but no luck down the interstate.

mt_goat

I see my hottest temps at highway speeds too. My take on it is that at idle the engine isn't working hard but get these high profile trucks up to highway speeds and they are putting out max HP.

Its posssible you have a slightly blown HG that doesn't leak internally (coolant into cylinders), but leaks out exhaust gases into the coolant at high load (like at highway speeds).

I installed a real water temp gauge to get actual numbers of what is going on.

I guess you have a good mix of antifreeze in it (to lower the boiling pt.)? And have a good radiator cap to hold pressure (also lowers boiling pt.)?

Sounds like you are either boiling the coolant or leaking exhaust gases into the coolant.

DanStew

What is the timing on the truck? It was under my impression that highway speed overheating is caused by timing being off. Because you can get residual air cooling to help the radiator.

ZUK

iTrader: (1)

Sounds like the brand new radiator is clogged up....when it gets hot again try the hand test....look for cool spots on the radiator surface.

mt_goat

I thought of that too Zuk, but he said its a new radiator. Although its possible the lower hose is sucking shut.

Litermonster

Well, I appreciate all of your advice. I will most def. check the radiator to see if its clogged. I need to replace the timing chain soon anyways, so a head gasket replacement sounds like a good idea as well. I am having trouble with these radiator caps, I go through about 5 before I get one that works. Maybe I will try that cheaper alternative first. Thanks

abecedarian

A fairly simple check you can make about the headgasket is to start the engine with the radiator cap removed. After the engine warms up completely and the thermostat has opened a few times (careful- it may spit out lots of coolant at you as it warms up), make sure the radiator is full and watch for little bubbles to come up in the radiator. Also, if you see a rainbow like film on top of the coolant, that is an indicator of gas or oil in the cooling system.