but the smog station can! I have an 88 4runner that I bought about a month ago. I drove it 70 miles home and taken trips to haul stuff around town. The temperature never gets more than halfway up. I finally got around to smoging it and the truck overheats during the smog when they do the load test. For those that don't know, basically they put it on a dyno and drive at 15 and 25 miles an hour and apply load to simulate driving. I left the smog station drove over every big hill around my house and can't get it to overheat again. Has anyone experienced anything like this? I want to reproduce the problem so that I can be sure it is fixed before I go back.

I don't appear to be losing any coolant, radiator is still full.

Suggestions?

thanks,
Jesse

 

Did they have a fan on the radiator on the dyno? It might not have been getting as much air as it needed in there. Fan or not your gonna get more air through there while driving.

 

Yeah, they had a fan, but you're right it will get more air driving. I just wonder what else I can do to lower the temps. I have to smog it. I was also thinking that I have larger than stock tires on it, perhaps that is putting just enough extra strain on the motor?

 

Yea x2, make sure they have a fan in the front of your truck.

 

Well when you're driving, you're getting the cooling from the air being forced onto the radiator and such. But on the dyno, the vehicle is at a standstill so there is no air flow like that. Make sure the fan clutch is good, the radiator isn't clogged and all the rest of the cooling system is in tip-top shape.

oh you guys beat me too it

 

So they wouldnt pass you because it over heated?

You could probly get it to heat slower by removing the t-stat. Also locking the fan clutch if that is possible. It might stay cool long enough to pass if that is the problem?

 

One solution might be the Taurus eclectic fan add on. You can usually find one at a junk yard and wire it in. I have never done it, but if I am correct...and I am sure someone else will verify or correct; it can be installed in front of the mechanical fan. It should solve that problem.

 

The problem was that they couldn't finish the test before the temp got up almost to red. I went to two shops because I didn't believe the first guy. I don't want to go back until I know that it won't overheat. If I take it back cold I might have enough time before it gets hot. I'll flush the radiator and make sure I have good flow and also check the thermostat, perhaps its not opening completely. I just wish I could reproduce it first so I know that its fixed.

 

If you take out the t-stat for the test it will let the water flow the whole time. Definletly heat slower. Give you a better jump on the test.

 

since you want to reproduce the problem, go drive 70 miles or whatever, park, idle and rev for a bit at 15mph and 25 mph.....

 

Make sure the heat isn't on.
Your truck will get to temp faster with the heat. I can't explain it properly but it's true. I've tested in my rig.
Wait, you're from cali, I doubt you had the heat on or ever had...

 

it still gets cold enuf in cali to justify turning on the heater... HEY 40 degrees is cold to us! lol.
remove Tstat, like everyones sayin. or to reproduce it, put the truck on jackstands and do your own test (wheels spinning at speed, but no air coming into radiator). that should reproduce the problem.

 

i'd say you've got a fan clutch thats not doin its job.

 

running the heat will usually actually help it run cooler as an outlet to help disapate the heat and prevent over heating

 

x2 The heater core acts like a second tiny radiator that keeps temps down

 

thanks guys. I have tried to reproduce the issue right after leaving the smog shop. Went up the biggest hill I could find going 25 in second. Still won't get hot. I can't use jackstands to test because the problem arises when they apply load to the dyno. I am going to tow my boat and try again if it gets hot at least I have a reproducible test. Then my plan is to do the following:

Check T-stat
Flush coolant and look for mud and poor flow.
Check lower radiator hose (these can collapse under load when hot if worn out?)
How do I check my fan clutch?

Thanks,
Jesse

 

Put small tires on. Like 28" street tires. Or, pump up your rear tires to like 45psi on your way to the test...

 

Still no luck. I towed my boat around for a while this morning. Went up the best hill I could find going 25 in second (like the test). Still won't get hot. I'm just going to take it in cold, hopefully they can finish the test before it gets hot.

 

just take the thermostat out and you will be good to go.....

 

Update: went back to the smog shop and had them put the fan on right away when they started. This time no overheating. I failed the NO portion of the test though. Here is what I have

High NO (1771 at 25mph, max is 866)
Timing check failed
I also noticed that Idle is very low

seems like my timing is retarded which could cause all of these issues (I think). How do I set the timing (or do I)? I am doing a search on this now. I also suspect the precat 02 sensor, could that cause these symptom?

Jesse