Engine Cooling Problems

Okay, here we go again. Just changed a broken timing belt. Everything works fine minus one little detail. My truck has done this for a while and I don't know how to fix it. Around town everything is fine. However, get up to interstate speeds and the engine runs hot. It has never broken the red-line, but it will get close. I know it's not the temp sensor because I've confirmed the problem with a mechanical temp gauge. New water pump, new radiator hoses, fresh coolant, no fluid loss anywhere. WHAT THE HELL??????!!!!!!:banghead:

More than 100K, consider the radiator. Are you sure the little tube to the reservoir and the inlet to the reservoir itself are open?
Did you do the tstat, too? It's been recommended to use an Isuzu tstat... What year is your truck? Which engine?

EDIT: I see from your other thread (and your screen name!!) that it's a 98 with 211K. And I'm guessing if that was your original belt, you have the original rad and it is time for a new one.

I had the radiator changed around mile 165k. The thermostat was changed at the same time as the timing belt and water pump. I've done everything I know to check the coolant system and was curious if there could possibly be a blockage somewhere in the coolant system itself. If there is something like that actually in the block, how would I go about flushing it out?

I had the radiator changed around mile 165k. The thermostat was changed at the same time as the timing belt and water pump. I've done everything I know to check the coolant system and was curious if there could possibly be a blockage somewhere in the coolant system itself. If there is something like that actually in the block, how would I go about flushing it out?

That's pertinent info...

You can use a flush available at the parts store. I used a Zerex flush once, and made sure I opened the drain on the bottom of the block to get rid of deposits it may have loosened. That'll get rid of some of the internal engine deposits. The rad must still be good if it only has 45K on it. Make sure that little hose is clear and the openings it connects to on either end are clear. Might be worth looking down between the heads to see if you missed a coolant leak there. You don't lose any coolant?

That's about all I can think of now...

Take a GOOD look at your a/c/radiator condensor, make sure there are no debris between the radiator and the condensor.

Is your truck an auto? If so, double check the level of ATF fluid, make sure that oil is not burnt or low.....they both use the same cooling system, one can overheat the other.

Find out if your thermostat is Isuzu oem, if not, this could be your problem...it's a very common complaint that non-oem thermo's do not keep the engine cool enough.

Alrighty then. It appears that I've got some work ahead of me. I completely forgot that the trans operates off the same system. That would make sense seeing as it doesn't act up until I get up to higher speeds. Thanks for that.
With the flush kit, is that a chemical that I just pour into the system and run the engine for a few or is it something I put in during the flush process? I appreciate every one's help AF is a kick butt invention.

I didn't get the kit, just a pint of flush that was added with distilled water after draining the old coolant mix out. I then ran the truck for about 10 mins and flushed that stuff out, then put in the new coolant/water.

With the flush kit, is that a chemical that I just pour into the system and run the engine for a few or is it something I put in during the flush process? I appreciate every one's help AF is a kick butt invention.
Depending how bad the flushed waste looks.
Just flush with water till it comes out clean, then add flush chemicals and drive it around an hour, and then flush and see how much crud comes out.

Commercial shops use a pretty good size pump to blast the system clean.
Getting creative, you could use wet vac and air hose to really move the crud out that won't move to just gravity.

Was it a new or used radiator? When replaced.

Test the heater core heat output as well. Flush those lines as well.

If the original coolant came out clean, then it should not be that big a deal.
Just that I've seen the crud come out solid rust all day flushing on some vehicles.

Radiator was new, I picked it up from the dealership. The heater core was by-passed years ago because it went out on me three times in one year so I've been driving around without heat for about four years. I drove it around for about an hour and a half this past weekend and it's not overheating anymore, so I'm guessing it did in fact have to do with the transmission. However, now I'm having a problem with it surging when I start it. After a minute I guess the computer starts compensating and everything seems fine, but it struggles to run for the first minute or two, then runs at about 2000 rpm and begins the slow down to around 900 rpm where it stays until it cools off again. What could that be? I'm so frustrated that I'd sell it for parts, but I can't stand the thought of my baby rotting in a salvage yard or being melted down for damn paper clips. Any help would be appreciated.:frown:

I don't recall if you have changed the intake manifold gasket yet?

I drove it around for about an hour and a half this past weekend and it's not overheating anymore, so I'm guessing it did in fact have to do with the transmission. However, now I'm having a problem with it surging when I start it. After a minute I guess the computer starts compensating and everything seems fine, but it struggles to run for the first minute or two, then runs at about 2000 rpm and begins the slow down to around 900 rpm where it stays until it cools off again. What could that be?
I'll try from memory, but I've been out of the dealer loop for a few years as service tech manager.
1. The reason I asked about radiator was in a weakened state and using chemicals, it can do more harm than good where they start to leak freestyle.
2. Odd about the tranny and overheating, but OK.
3. amigo2k mentioned intake gaskets, and indeed intake vacuum leaks can cause odd symptoms. We'll get back to this in a moment.
4. Usually cold running issues can also be a bad cold start injector, if it applies. It's usually included on most systems, but I'm not sure on ours.
3a. One painless test of vacuum leaks is while engine is running.
I'd start first inspecting most connections to see if any vac hoses are hard as rock, then trim them back to soft section and install if enough slack is there.
While engine is running, use a can of just about anything flammable with a spray tube.
I'd rather you did not use starting fluid for obvious reasons.
Carb cleaner is a little harsh, and will possible damage plastics.
Brake / Contact cleaner is a better choice.
So the best all around easy to get chemical is WD-40.

We are going to be spraying product at the engine, at every possible vacuum source.
This will be focussed at the gasket edges of intake manifold, all hoses, random joints from the throttle plate inward.

The spray tube is an important tool, as it will pin point the spot if the engine responds to being sprayed in that zone.
You can test spray some into the intake and now notice how engine will respond.

ALL this will be contained between the valve covers, and the intake manifold, so no need to get near the exhaust manifolds.

In the end, if no results are noticed from testing, then you may need to get the scan tool for codes of who wants attention. Loosen gas cap just incase a sensor detects it.

Too bad about the heater core. At 30 below here, I'd have no choice but get that going. Or a hot boulder from the fireplace. I tried to get to work one day with out heat and ended up taking out the windshield in traffic. But that's comedy for later.

The heater core is also a safety device for when the engine does go extreme overheat by using it in full heat output to assist the engine in cooling it from the back side. The difference between a blown head gasket without it on, or continue as normal.

Good Luck, and we'll check back.

I am having a similar problem with an '01 Rodeo, 6cyl. Replaced EVERYTHING including water pump, thermostat, radiator, and fan clutch. I am going to do a coolent flush today.
Truck overheats at idle. Temp on the radiator stays cool and we have flow but engine temp rises. If I bring the idle up to 1100 RPM in Park then it starts to cool down.

Oh, and the crazy idle , start problem from above. I had that as well after replacing the gaskets / thermo.
Switch the two vac hoses on that valve at the back drivers side of the intake. One goes to the vac resoirvoir and the other to the vac acuator that opens the second set of intake runners. If they are backwards the second runners will open (or not open) all the time. Ran into this last week.

I am having a similar problem with an '01 Rodeo, 6cyl. Replaced EVERYTHING including water pump, thermostat, radiator, and fan clutch. I am going to do a coolent flush today.
Truck overheats at idle. Temp on the radiator stays cool and we have flow but engine temp rises. If I bring the idle up to 1100 RPM in Park then it starts to cool down.


I have a 96 3.2l auto 212k. I am also having overheating problems at an idle. new waterpump, t-stat, intake gaskets and coolant hoses under the intake manifold. cant figure it out. hasn't gone into the red, but close. gotten hotter than I am comfortable with thats for sure. not an oem t stat. i think I will try that first.

Sounds like a head gasket to me. Do you have bubbles coming up in your radiator if you run it with the cap off? A little steam out the exhaust?

actually no i dont. there is no mixing of the coolant and oil either.

kaufman....you didn't mention if your radiator's been replaced?...DEFINITELY get that t-stat OUT if it's not oem asap!

Non-oem t-stat's are notorious for causing the engine to overheat, they don't keep things cool enough.

Remember, every time you overheat your engine, you cook your tranny too....cooled from the same system. Highly recommend doing a partial drain/refill on your auto tranny soon.

If your radiator is 7-10yrs of age, it's probably toast internally and not cooling efficiently, also double check your fan clutch...make sure it's working correctly.