86 4.9 strait 6 overheating

Love this forum, very helpful.  I have been looking through threads for an answer to a problem, maybe someone can help.
86 4.9 strait 6:
Over heats if you drive it 55 for awhile (say 30 min).  Never actually gets out of the 'NORMAL' range but pretty close (hits the L).  The oil is normal color, coolant is rusty colored.  I have flushed the coolant system with no improvement.  New Tstat (tested the old one and it opened right at 195 anyways)
What should i be looking at?
Head gaskets
Water Pump
those are my suspicions and i really hope its the water pump.

I wouldn’t trust the gauge. I would stop and check the temperature of your engine at the thermostat housing with a infrared thermometer.

I put a new sender in mine sometime back and it read better but not consistent. I have an aftermarket gauge in it now.

Welcome!  

If the coolant is really that rusty it's very possible the impeller is rusted to bits as well.
Is the radiator caked with rust inside?  That will really cut down on heat transfer.

Do you have an IR non-contact thermometer?
Perhaps you could run the engine without the radiator cap on until the thermostat opens.
You should then see a substantial flow across the top of the radiator core.

IIRC Scott ran gallons and gallons of distilled water and magic elixir (Thermocure) through his cooling system before it started to come clean.
That starts about here.....
People don't realize how important having the proper concentration of antifreeze is.
Nor do they bother periodically changing it.

My first lesson with radiators was as a teen. I noticed temps climbing on the freeway only. As I slowed down, temps fell.  So I drove slower, later went to NAPA, and ordered a radiator.  Problem cured.

This is a classic scenario of insufficient heat transfer capacity. Internal scale buildup in the radiator insulates the coolant from the air outside. You only know it at higher speeds, when the engine is producing more waste heat.

Especially if you have rusty coolant in there, I'd replace the water pump and radiator.

You make a good point that if there is enough circulation at low engine speeds there shouldn't be a problem with the water pump turning highway rpm.

I'd still want to see poor circulation before I dug into changing a water pump.

And I'd probably do whatever I could to get the sediment out of my block before replacing anything., but it does seem like the radiator simply isn't shedding enough heat.

I think that only 300's with air-conditioning have a proper shroud.
(which says something about having one overheat!)
But the extra cooling radiator and shroud from a truck with air conditioning should be a straight swap if yours doesn't have one now.

I agree on the radiator. Had a 4Runner do that on me, temps would come up climbing through the mountains.

My truck comes up a bit now at highways speeds and climbing. Looking at aluminum radiators.

Awesome, I appreciate the advice!  I am going to try and flush the block while checking the flow through the radiator.  I have a radiator and water pump in my basket at rock auto along with an after market temp sensor.  $150 for everything isn't too bad ( I already have a bunch of new coolant).  Thank you all for the advice, I will post my results!  

I hope you find the problem.  

You might consider new hoses and clamps while you're making an order.
The lower hose can get really crusted onto the water pump when the cooling system is that neglected.

ArdWrknTrk wrote

I think that only 300's with air-conditioning have a proper shroud.
(which says something about having one overheat!)
But the extra cooling radiator and shroud from a truck with air conditioning should be a straight swap if yours doesn't have one now.

FYI
Yes only the 300 with AC (and maybe HD cooling?) use a shroud and larger radiator.

No it is not a straight swap as the radiator support has a bigger opening on the AC trucks.
When swithcing mine from non-AC to AC I had to use the radiator support from the AC parts truck as it has a bigger opening.

Now I dont know if you can cut the opening bigger or not and if the holes / nuts are in place for the hold down brackets.
IIRC there are 2 different types of radiator hold downs also, early & late.
I think the early supports have the needed holes & nuts to use the bigger radiator.
Dave ----

UPDATE:
New water pump, radiator, thermostat, hoses and radiator cap....now it stays at NO of "NORMAL" and there is a HUGE difference.  Thanks for all the advice!  The coolant has been flushed multiple times and is now finally starting to change to a less rusty color.
THANKS AGAIN!

Sweet! Good job!

Excellent!  Glad it worked out so well.  

Yes good the truck is keeping a cool head LOL

FYI if you replaced the lower radiator hose I hope it has a spring in it.
If the new hose dose not have a spring and it most likely dose not you have to use the spring from the old hose.
If you do not use a spring in the lower hose when the RPM goes up the hose closes up and you then have no coolant flow.
This will show up more on long high way runs than in city stop & go driving.
Dave ----