4.3 runs hot on the highway

[John Stanley]

I'm a little baffled by this problem and have had a good opportunity to
observe my engine today. I recently blew a lower radiator hose and had a
major overheat subsequently. Since then I'v replaced both radiator hoses and
the thermostat, the water pump was replaced last year due to it leaking. So
now, in the heat of the day ( live in AZ) I can run around anywhere up to
50MPH with the AC cranked and the engine temp will stay fine. As soon as I
hit the freeway and am going upwards of 60 to 70MPH, the engine gradually
starts overheating (takes about 15 minutes to hit the 210 mark and keeps
going). Today, I was driving down the freeway and the engine temp was too
high so I got on a frontage road and kept speed around 45MPH and turned the
heater on full blast to dissipate some of the heat. The temp went down to
normal in a matter of minutes, however I didn't keep the temperature once I
went back on the freeway even with the heater still cranked. This weird temp
behavior all happened after I had that big time over heat which pegged the
temp guage. I don't know what it could be. Is it possible the pump was
damaged and isn't working 100%? Is there some sensor that could be damaged?
I can tell the engine is overheated by the way it responds to acceleration
and its sound, sounds like its revving high and acceleration is sluggish,
just in case the gauge sensor was faulty.
Anyway, I back flushed the system today in hopes of cleaning out any kind of
buildup anywhere but it didn't help this problem.
Any ideas? It seems to be dependent on ambient air temp as it doesnt' happen
at night, but if its 90+ degrees out (approx) the overheating occurs.

thanks,
js

[Greg]

Once you heat them to the red its time to rebuild, however did you check
the spring in the fan clutch? if it got to hot it might have went past its
winding. When you heat them like this you can break a ring or rings and
cause the cylinders to heat up. also the oil in the rings at the time will
make the rings stay in . oh boy .
John Stanley wrote in message ...

[John Stanley]

Greg <pi...@neworld.net> wrote in message
news:92941168...@news.remarQ.com...

> Once you heat them to the red its time to rebuild, however did you check
> the spring in the fan clutch? if it got to hot it might have went past its
> winding. When you heat them like this you can break a ring or rings and
> cause the cylinders to heat up. also the oil in the rings at the time will
> make the rings stay in . oh boy .

thanks, since a rebuild is way out of my league and financial situation, I'd
like to go for anything else that it may be. Would the fan not spin at full
capacity if the spring went past its winding? Or would it just not spin at
all?

js

[Terry & Michelle Pattison]

If the fan were causing you overheating, it would spin freely by hand, even
after the truck is heated up. Have you had your radiator checked to see if
there is any blockage in the channels causing poor circulation? Good luck
with your truck.

[John Stanley]

Terry & Michelle Pattison <patt...@eagnet.com> wrote in message
news:92958589...@news.remarQ.com...

no, I'm trying to keep it as DIY as possible on my student income. I guess I
may have to get it checked though. Funny thing is, it keeps all its coolant,
so the blockage thing is a pretty good guess.

js

[riverrat]

Intriguing...

You are either: producing more heat due to damage, failing to dissipate heat
as well as before or entering a warmer season than the cooling system could
have supported even without the hose failure. Whatever, you are making heat
faster than you are taking it away so temp goes up until condition is
changed.

Let's assume that engine is not damaged. What else happened? Did shroud get
damaged? Was everything in air-flow path replaced correctly? Can air get out
of engine compartment after going through radiator? Is belt OK? Or is it
glazed and slipping to slow down water pump? Was "new" water pump correct
part and hot-weather tested (prior to hose failure) or could it have been a
problem lurking through the winter? Did you install headers?

How about the exhaust system. Is it running free when engine revved? Carbon
can block flow. Dual wall pipe can collapse inward during freeze and close
down flow. Once limit reached engine works very hard for each additional
rpm.

As for engine: "sounds like its revving high and acceleration is sluggish"
means fan clutch is responding to elevated temperature as it should --
unless tranny is slipping (which makes copious heat!!!) Is it using more
oil? Smoking? Making unusual noises? Using more gas? Losing power? If not,
look everywhere else first!

I've heard of miracle stuff to help water dissipate heat better. Supposed to
drop temp up to 40 degrees, is expensive and is advertised in street rod
mags -- may be worth a try (as next to last resort...)

Good hunting, and let us know!

[chris]

well john what you more than likely have is a head gasket or head problem
more than likely a head gasket .slight exhaust leak into the cooling system
not big enough to cause a loss of coolant . we have had this with quite a
few engines regardless of nameplate best test is infrared exhaust analizer
any h.c. in the coolant and thats all it takes. h.c.= hydrocarbons if you
can get someone to test with their infrared be sure to drain the radiater
some so that there no chance of getting liquid into the machine does not
like that ... one test you could do is get on a good long hill and
keep the speed around 35 and accelerate up the hill if it gets hot that
way too pretty good confirmation. unfortunately a head gasket job is not
cheap
good luck shadetree
John Stanley <nonjr...@smarthealth.spam> wrote in message
news:J4d93.2175$V4....@news.goodnet.com...

[Ken Kicak]

Does the cooling system on your vehicle need to be bled? (Your problem
sounds exactly like what would happen on a vehicle that has air trapped in
the cooling system).

[fetz...@my-deja.com]

In article <J4d93.2175$V4....@news.goodnet.com>,

You may want to re-check your thermostat. The only times I've seen the
problem you describe, is when people completely remove their thermostat
thinking it will make their engines run super-cool. But that's a
mistake.

Without the thermostat in place, at freeway speeds (higher
engine/waterpump rpm) the coolant circulates too quickly through the
radiator to get cooled off, and the engine eventually overheats.

I suppose a stuck-open thermostat might create the same problem. But
that's usually not the case because even a stuck-open thermostat
restricts coolant flow enough to avoid the problem.

Check it out though, if that's it, it's a cheap fix.

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[VWBugfarm]

Check to see if your bottom raidiator hose isn't colapsing. If it doesn't
have a spring in it , it may do that. Be carefull though looking under the
hood at 70mph might be a little dangerous.