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Cool motor, hot engine bay

R

RaccoonJoe

NAXJA Forum User
Location
Fort Wayne, IN
I've noticed recently that the temps inside the engine bay seem to be extremely high, while the temp gauge in the dash seems to be reading low. I'm pretty sure that the gauge is functioning, as it will peak ~205 just after startup, and climb back up to 190-200 while idling through town. However, on the open highway, I'm looking at temps of ~160, constant. Any idea as to the cause of this?? I'm looking towards doing a vent setup, but can't seem to find anything I like. Might end up with hood spacers.....

BTW....I'm just shade-treeing here....don't have access to a IR temp gun or any other fancy tools.

89 Renix XJ, 4.0L, closed cooling system, 218K miles
 
Super low temps if they are real. Maybe the sending unit has shot its wad. No way to tell w/o a temp gun unless you put a new sender in and see those gauge readings.
BTW no matter what everyone else says in the future I'd keep the closed system.
 
Ill disagree, Dont understand why you'd want a LESS serviceable system, as the closed system.

Not sure why you'd wanna' risk getting stopped early on a trail ride over a plastic bottle either.

But , from the sounds of it, your factory gauge is off.

Start by replacing the temp sending unit.. $3 or so...

If its the same, put in an aftermarket gauge w new sensor... and go from there
 
Check to see if the exhaust manifold is leaking from a bad gasket or cracks around the collector. Hood vents are an effective way to remove lots of heat from the engine compartment. You can also wrap the header and downpipe with header wrap available from lots of sources like Jegs or Summit racing.
 
Blaine: I'll agree with you on the hood spacers..that's the one thing I don't like about it. Maybe I'll only lift it 1/2 inch or so....

To the others....I plan on keeping the closed system in place, until I have something fail. Then, I'll look into switching it over, and figure out what's the easiest route to take. Don't know exactly why....I just like the old, closed loop better.


Could this be a sign of a thermostat going bad?? I *hate* to throw parts/money at a problem.....
 
Joe a closed system is under more pressure and thus under pressure it can tolerate higher temps without boiling over. Higher temps are encountered on trail runs and pulling loads and uphill climbs and crawling up trails etc....
Hood spacers are a bad idea. Hood vents are better, but a rear facing hoodscoop would be ideal. I'd have one if I was able to do bodywork.
 
Just as a test before the spacer thing remove that big rubber piece that goes across the top of the firewall, that rubber piece that seals the rear of the hood and see what happens.
 
Speed_racer said:
Ill disagree, Dont understand why you'd want a LESS serviceable system, as the closed system.

Not sure why you'd wanna' risk getting stopped early on a trail ride over a plastic bottle either.

But , from the sounds of it, your factory gauge is off.

Start by replacing the temp sending unit.. $3 or so...

If its the same, put in an aftermarket gauge w new sensor... and go from there
Click to expand...

Thats the way I see it also....I'll never go back to the closed system.
 
What temperature thermostat do you have? If it is a 165 F thermostat the fan clutch may be bad. If it is a 192 F thermostat it might be the wire conection to the sensor is loose & dirty, but a lot of your description sounds like the fan clutch

RaccoonJoe said:
I've noticed recently that the temps inside the engine bay seem to be extremely high, while the temp gauge in the dash seems to be reading low. I'm pretty sure that the gauge is functioning, as it will peak ~205 just after startup, and climb back up to 190-200 while idling through town. However, on the open highway, I'm looking at temps of ~160, constant. Any idea as to the cause of this?? I'm looking towards doing a vent setup, but can't seem to find anything I like. Might end up with hood spacers.....

BTW....I'm just shade-treeing here....don't have access to a IR temp gun or any other fancy tools.

89 Renix XJ, 4.0L, closed cooling system, 218K miles
Click to expand...
 
Where are you folks finding these $3 temp senders?? My local parts store has the temp sender, but they want ~$12 for it.

*Not that I'm b!tching too much about the small difference....but there's got to be some better places to get parts..........*
 
No, I meant one that is not locking up when it should. The cooling fan clutch.



Blaine B. said:
You mean a bad clutch that is locking up when it shouldn't?
Click to expand...
 
He said his temps were fairly low though.

For the GAUGE sender, ONLY go to the dealership. Something about calibration between the OEM gauge and OEM sensor, yadda yadda yadda......it's like $14.
 
You gatta read between the lines on these nobe posts. He mentioned it running hot...idling, then cold on the highway.

It could just be a 165 F thermostat in yours. Mine runs cool on the freeway, A/C off at 165 to 175 F depending ambient temp, then 195 to 205 F idling with AC on, or 185 to 190 A/C5 off while idling which is normal for mine. I have a 165 F thermostat, non-oem. Thats based on 70 to 90 F ambient on mine. My entire cooling system has less than 10,000 miles on it (except the water pump).


Blaine B. said:
He said his temps were fairly low though.
Click to expand...
 
Blaine B. said:
Hood spacers. I don't know but in a collision, it looks like the hood would be perfectly aligned for a neck-slicing.
Click to expand...
Yea the spaced hoods Ive seen look like they would go right thru the windshield. My gage is fine and my engine bay temps are crazy hott it seems:firedevil
 
I just had the same issue on my Renix era motor. Turned out to be a LOT of air in the system, I bought an inline filler neck to help bleed out the air and when I cut the upper hose in half, it was completely full of air. I then cut the upper heater hose in half to install a t-fitting so help bleed out air and that hose was full of air as well.

I ended up just putting the filler neck in the upper hose and a 't' fitting in the heater hose and I eliminated the pressure bottle and heater control valve. The heater hose goes from the front of the motor to the heater core back to the motor. Its never ran at the same temperature so consistantly now, I have put about 2000 miles on this setup, including a 17 hour drive in 97 degree weather and the temp has only made it to about 215 three or four times.
 
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