motor runs a bit hot when a/c is on

[pinoy99]

Several weeks ago, I noticed the temp gauge creeping towards 'H' during a stop/go drive while the a/c is on. After shutting off a/c and turning on heat, the needle settled back in the middle. Subsequent trips with no a/c on, temp shows normal(middle).

Drained and re-filled the radiator last weekend; short city run with the a/c on have the needle just a tick below mid-point. Ran 80 mile trip one way with no a/c, temp remains normal. Return trip on 90+ degree weather, with a/c on, mostly highway running at 65-70, at times the needle creeps up again but shutting a/c down temporarily bring the gauge back to normal again.
I think it would run very hot(maybe not over heat) when used in traffic with a/c on.

Upon inspection of the fluid level after a short run right after the drain/fill and with the radiator cool, coolant is full but the rad cap and the neck of rad has rusty colored sediments which was removed by simply using paper towels. This also occurred after the first 80 mile run. I have not yet checked again if there are more crud coming up to the top.

Should I have the rad flushed or just perform another drain/fill to flush out more of the old coolant? Suggestions/advice appreciated. Thanks.

This is for a 99 Isuzu Trooper with belt driven fan, 180k+ miles, original coolant replaced during t-belt/water pump replacement @90k.

 

[Mud]

IMO you are waiting too long between coolant flush/changes - running the coolant to almost 100K is asking for sediment buildup.

Sounds like more of an airflow problem and my guess is that the engine/radiator is getting gunked up internally. You may not be able to see the buildup just by looking down the neck. When you turn on the a/c you are adding more heat to the system by using the condenser that is in front of the radiator. If the cooling system is marginal, then the added heat cannot be dispersed. As time goes on, the temp will rise even with the a/c off.

I would suggest a good POWER flush of the entire system followed by having the radiator rodded out/replaced. Running a garden hose through the radiator won't cut it. I do my own work and it's easier for me to simply by another radiator (I've had good luck with radiatorbarn.com) and drop it in than having the time and trouble to get the old one cleaned out. Replace the thermostat and radiator cap at the same time.

Something else to ensure is that the fan clutch is working properly. You did not mention anything about hoses - if those are original then it's time to think about new ones while the system is drained.

Summer is here and some maintenance now could save you grief later!

 

[HondaMan]

I feel Mud is right on about the fan clutch.

I had a very old Toyota with similar problems and was told it was the fan clutch which did not seem right to me as the fan and motor/clutch seemed to operate fine. Well... when I finally did change it out... bingo.. overheating problem solved. fyi.. this can be a $$$ part.

 

[BigDenCCMD]

pinoy99

I'm not a mechanic (but I did spend the night in a Holiday Inn Express!) but I'm given to understand that the motor oil has equal or greater effect on heat. So...what kind of oil are you using?

Someone else may say that this is not the case and I may be all wet (excuse the pun). I also agree with checking hoses etc.

 

[motorguy222]

It could be a few things.

1.The thermostat may be going bad.It may be starting to stick.

2.The rad is in need of a good cleaning.It is clogged.

3.The water pump is going bad.It isnt moving coolant like it should.If it is going bad,it cant keep up with the extra temp caused by the AC.

4.The rad is old,it needs changing.They can wear out,the fins on the rad get old and no longer remove heat as they once did.

To check the rad,lightly rub your thumbnail along a line of the radiators fins.If they fold over easily or crush or crumble,the rad probably needs replacing or re-coring.

If the fins are bad,the rad can not cool like it once did.

It sound that it is quite possible that the rad is just old and the fins cant remove the heat like they should.

 

[mechtech]

How about checking/cleanig the crap in front of the condensor and radiator? They get plugged with leaves, bugs, and debris, over time.

 

[pbm]

Pinoy99: I just got my July 05' copy of Popular Mechanics in the mail and the Car Care section (pg.115) has a 'How to' article on Fan Clutch Replacement. It seems to be informative. I hope this helps.

 

[robbobster]

The fan clutch may have an impact on low-speed cooling, but at anything approaching highway speeds the fan is useless as you get pleny of airflow.

Since his problem happens at highways speeds as well, so there may be some other culprit involved. Though the fan clutch may have an impact on his low-speed cooling performance (or lack thereof).

I bet that radiator is chock full of crap, as Mud noted.

 

[Matt_S]

If it were me, I'd get a bottle of heavy duty radiator cleaner and flush the system through with it. Use one of those flushing tees and thoroughly rinse it out after you're done. I obviously agree with those who feel the radiator is clogged. It may be clogged enough that you need a new one, but it's worth a shot to clean it, although a simple drain and fill won't be enough.