Overheating '97 Rodeo

[Beergeek]

I have searched the forum, and read a few of the posts. But I think my symtoms are a little different:

I tend to overheat faster at highway speeds. The faster I go, the faster/more I overheat. I don't have the problem driving city streets, stop/go traffic.

I have flushed the radiator twice. Seems to have helped a little, but maybe it was just a cooler day.

I changed the water pump at 160K, and currently I'm at 190K. The old water pump looked fine.

I took the thermostat out a month ago. Doesn't seem to matter.

I think (I hope) it's down to the fan clutch or the radiator. I saw one diagnostic in here for the radiator I haven't tried: Start up cold, run a few minutes, shut the motor down, then feel the radiator to see if there is a temperature gradient, indicating a plugged radiator (it seems to flow fine when flushing).

Is there a good diagnostic for the fan clutch?

[Ramblin Fever]

Fan clutch is mainly the culprit if you're sitting in slow moving traffic, and/or idling with very little air flow.

Fan clutch isn't truly needed at highway speeds.

I replaced my radiator a few months back due to what I felt was minor clogging, but it was 10yrs old and I just felt it was time; even with antifreeze flushes every 1.5yrs. It was not overheating, or even over half on the gauge - but, I had an older truck that overheated at it's 10yrs of age due to a bad radiator/hoses and it caused a boat-load of issues that I didn't want to deal with on another.

On your thermostat, I know you said you took it out but - if that is the original, get it out and replace it with OEM Isuzu thermostat ONLY!

Do NOT use any other thermostat - they do not keep these engine's cool enough, and if one is running with a therm not OEM, it is possible to overheat.

Another thought - you didn't mention if your truck is auto or 5-spd, but if your auto tranny is overheating - lack of fresh ATF (every 25k miles), torque convertor slipping, ATF leak, resulting in low ATF - it will overheat your engine, too.

They are connected via radiator, if one overheats, the other will too. So also make sure - if you have the auto - that your transmission is up to spec as well, and remember every time that gauge pecks Hot, your tranny is cooking too.

Check for any coolant leaks under pressure, but too me, kind of sounds like a clogged radiator; you could try pulling it out and cleaning the fins really well; or just replace it - they're typically about used up between 7-12yrs.

Check your oil, make sure you don't have coolant mixing in - if it's overheated more then twice, sometimes once is all it takes, a head could crack/warp very easy due to the all aluminum design.

Make sure to change out your ATF fluid too - as soon as the overheating issue is resolved, or you could lose your transmission as well.

Please keep us posted.

[Beergeek]

Thanks for the input!

FWIW, my Rodeo is a 5 speed. Per the tip elswhere in the forum, I drove a few blocks at lunch, and felt the radiator. The bottom is cold, the top is hot.

I think that's pretty much a smoking gun. I'll start looking for a replacement radiator, then change out my oil. I have to get the OEM thermostat at the dealer, no?

opcorn:

[Ramblin Fever]

Look at autopartswarehouse.com for both radiator & thermostat - OR, check with Napa, this is where I got my radiator. You're looking around $175-200 easy.

Try NOT to be driving that truck, the more it gets hot the more headgasket/head damage you're doing. I know it's hard when you're limited to 1-2 vehicles, but it will save you many $$$ by not continuing to drive it until it's fixed.

We ignored this very suggestion on a late Toyota and wound up spending the greater part of $3-4k replacing the engine/heads, everything.

[Beergeek]

Changed out my radiator and thermostat, and gave it an oil change.

All better.

Driving home in 80F+ weather with the heater on full blast was getting old.

Thanks for the help!

[Ramblin Fever]

You're very welcome.

FWIW - these trucks/this engine does GREAT on Rotella synthetic 5w-40 diesel grade oil with a Napa Gold filter - specially in summer. But can be used year round for excellent protection.