Overheating issue...

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Nov 15, 2008
Tampa, FL
Hey guys, thanks in advance for reading!

I've got an '81 40, recently did a bunch of upgrades to make the cruiser more kid friendly as an open cruiser in Florida isn't much fun for kids given 90+ degree weather 9 months of the year and T-storms almost daily!

I added a trollhole top, bench seat, metal tech cage and lastly a Vintage Air A/C. I have the cruiser desmogged (I performed in 2010) with a Trollhole carb. When I replaced the A/C I went ahead and replaced the water pump, temp sending unit, new hoses, thermostat and housing (found it was cracked). It has a stock 81 fan (nylon) and fan clutch (works).

She is a beauty now... but I'm now very close to overheating and have had to stop driving a couple times after a quick 5-7 mile drive as it was approaching "H". I've read several posts about overheating (and know a fair amount) and I'm hoping that this isn't caused by lack of airflow due to the new condenser in front of the radiator (recommend location by VA system).

I "burped" the system tonight and got ZERO air. I used an infrared gun to check temps. With no A/C and idle temps were steady in the 125-135F at the top radiator, about 15 degrees lower at bottom of radiator and 140s near the temp sensor. With A/C on temps jumped about 10-15 degrees and then added 1500rpm and temps quickly jumped to 180's at top of radiator and higher near the temp sensor. It actually caused the "burp" funnel to overflow due to expansion and spilled causing the belt to slip so I stopped it before actually getting to "H".

I know there are 50 things that "can" cause overheating, but my cruiser gauge was usually about 3mm from "C" before I did all this work. Could it really be all from the condenser?? My cruiser is an 81 and a fair number came with A/C from the factory?

Given top of radiator and hose are so hot the water pump and thermostat have to be working (correct?)? The temp sensor seems correct, I would assume 180-190 are very close to overheating (correct?). She purrs like a kitten and there is no air in cooling system or fluid in the oil so head gasket isn't blown (yet).

If the condenser is causing all this what are my best options? Better new bigger radiator? I don't think an electric fan is going to do enough. Can I move the condenser? There have got to be a lot of 40's out there with VA A/C systems... I can't imagine they all overheat!

Thanks for help!


What brand of fan clutch did you buy?
It's not overheating. If anything it's running a little cool.

A 180° thermostat starts to open a bit above 180°. A 190° t-stat a bit over 190°.
I don't have the brand of fan clutch but when hot it is running at full speed and difficult to turn when engine is off (engaged). Sounds like a damn jet in my garage from all the air movement. Same fan previously used prior to the coolant work and A/C addition and had low temps as previously described.

So if the thermostats only open at 180 or 190, what should I consider "overheating"... I thought anything over 200 was bad but maybe my temp sender is more sensitive than previous and its running hotter but not "too hot". What temps are expected during load (city driving in FL with A/C running)? At what temps should I be worried?

I've blown a head gasket in an old truck letting it overheat so I'm a little scared to let it run up to high temps... am I being overly concerned?

Thanks again!
Nice 40! 210-220 is where I get worried but shouldn't really overheat until 240 or so if the system is tight and has 50/50 mix... my 40 loves 180-190 and when I wheel it runs there all day long. At around 160-170 is where the valves quiet down and it starts to run well.
So this could be a temper sensor issue if it's gauge is reading "h" at 180.

Where should I measure the temp for most accuracy with the infrared(next to sensor?)

Maybe I'll replace sensor with OEM (I think used aftermarket) and see if that makes a difference. Thanks. I'll update thread if that was the problem.
Shoot along the passage side of the engine block with the temp gun, I find that is a pretty good spot to get a good reading.

I agree, does not sound like your overheating.
As per the FSM, the 180 thermostat starts to open at 180 and is fully open at about 203 deg. I have the stock gauge plus a mechanical temp gauge on mine and the highest temp it ever shows is 200 deg., and that is on 100+ deg. desert weather after getting off the freeway at 60 mph. Then it slowly starts to go down to 190 then 180 deg. on city streets. It will stay at 180 deg. all day on city streets.
If a little coolant spilled on the belt is enough to make it slip, then you need to tighten the belt.
I don't believe you have a temperature issue at all. I believe your issue is that you are trusting the stock gauge, which is probably malfunctioning, or the sender is bad. If you actually want to monitor your engine vitals I highly recommend installing aftermarket gauges to complement the stock ones. The stock gauges are nice to look at, but I don't trust them to be very accurate.
I have replaced the sender with a new OEM and ran it for 20 minutes with a/c in traffic. It was approaching "H". Checked temps and they are 205-215 at top of radiator and at the sensor. I don't trust the hose temps using the infrared thermometer as the top hose temp is reading about 15 deg lower than the top of radiator. Regardless, the lower hose temp is about 15 degrees lower then top hose so the radiator is working.

Agree with above that belt needs to be tightened! Hasn't slipped during driving but I'll do it anyway.

Marshall, here are the pics. It's very tough to see the condenser as it is behind grill, literally 1/2 inch from front of radiator. Top of condenser is about 3 inches above "Toyota" grill emblem (vintage air recommended location) and it is as wide as stock radiator.

So it sounds like I'm very close to overheating, not just a gauge issue. Anyone with a VA A/C system having this issue with stock cooling system? Anyone have additional thoughts?

Thanks for all the suggestions!
Are you leaking water out your welsh plug?
No leaks...coolant full with overflow working.
I went through the whole overheating process when I first bought my 40. One day while driving along the beach on a windy day the temp started going up again, but when I turned around and started heading back the temp went down to normal again??? I realised then that going up the beach I was travelling with the wind and heading back I was going into the wind. So my overheating issue appeared to be airflow related. I always thought the fan and viscous coupling were okay, but after refilling the coupling with oil it solved the problem completely. I guess the fan was spinning but wasn't engaging enough to draw the air through the rad.

Sorry about your overheating challenges. From experience I know this can be quite frustrating. First thing, of course, is to check the things that you changed which, for the most part, you seem to have done. Along those lines though, you might consider Efjay's experience. He might be on to something and worth checking out. It just might be an issue with the new clutch fan.

However, when you get really desperate, you might want to check one other area. Perhaps you have already done this. I finally resolved my overheating issue by discovering my vacuum advance was no longer working in the distributor. Thus, as in your case, when engine RPM's increased, up would go the heat. This was found during a smog inspection. Just an idea for you to check. Good luck.
So after a year of only running the A/c a few minutes at a time... and almost overheating every time, gauge pegged to H, IR temp over 220 on thermostat housing. I decided enough was enough and replaced the radiator. Got a bolt-on replacement from Cruiser Corps, Aluminum champion model. Took 2 hours to remove old and replace new, it was pretty damn easy given the radiator frame that stays in place so the A/C components didn't have to be disconnected. She's back to running cold. Thermostat housing temps in 180's with A/C on, idling in 90 degree weather. I just figured with new water pump, temp sensor, thermostat, coolant and just added A/C that I probably knocked some rust off in the radiator during installation and it was causing issues. Turned out to be right.

I'm still having belt slipping issues with a 25-9590 napa belt (outside diameter 58.77). Tried previously to fit shorter belt but could't get it to fit. Anyone have this issue? Looks to be partly due to such little contact with the belt and the waterpump/fan pulley and the angle/location of the A/C pump on the Vintage Air system. (pics of the waterpump and belt are above).

Anyone had this problem? Installed a tension pulley or maybe a second belt from crankshaft pulley to the waterpump?

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