Running Hot on Freeway

If the e-fan is connected backwards the engine will overheat at highway speed if the fan kicks on. The fan would run backwards in this case. This wouldn't be as noticeable at lower speeds.

Over 35mph the fan doesn't do anything.

or

If you need a fan at 35 mph something is wrong.

Dirty Rick said:

Over 35mph the fan doesn't do anything.

or

If you need a fan at 35 mph, something is wrong OR you have a big IC and condenser blocking the air flow, and maybe you need to look at how well the ducting in front does to funnel airflow into the radiator instead of around it.

Or you need to live in cooler climate.

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Fixed.

Does the 7 series have a "splash shield" similar to the 200 series cars? If so (OP), is it in place? That piece creates an area of low pressure below and behind the radiator which helps draw air across the radiator when the car is at speed. If that's missing, it's likely contributing to the problem.

Thanks again everyone,

I definitely did not think of the fan running in the wrong direction, thank you lummert. Just checked and it pulls the air into the engine bay as intended.

I was under the same impression dirty Rick. But as dbarton suggests maybe the air is being directed over the radiator coils in the most effective way. I have some rubber "gasket/trim" type stuff I kept from another vehicle to fill the gaps between the condenser coil, IC, radiator. Also, when I replaced the radiator I sprayed the coils for the IC and a/c, cleaning opposite the direction of air flow. I used to clean a/c units for homes and never needed to use this stuff but maybe I'll try some of that coil cleaner they sell.

And yes mhyount I do have the splash shield installed, thank you.

Thanks again everyone, I'm getting my IR mid week next week so I'll have some fun with that and post back with what I find. Appreciate all the help and discussion.

Something else less likely to consider, is the engine mechanically timed properly? I’ve bought a 940 one time that was one tooth off (can’t remember if it was advanced or retarded), and under load the engine wanted to run much warmer. Might not be your issue though.

Keep in mind this was a 940, so the camshaft also drives the distributor which effects ignition timing (even though its computer controlled).

Thank you for the response. You know when I thought to start this thread I was wondering if it was something with the engine causing the warm running. I had the timing light out maybe 3-4 months ago to set idle speed and the timing showed 12* btdc. Or whatever the specification is, I think it's 12 though.

Also, the spark plugs look normal and at idle at least the a/f ratio is stoich (using a test light for lh2.2) and O2 sensor swings between ~0.1-0.9V.

How old is the “newer” radiator?”

And a question for all as I know nothing about these engines - if timing was advanced enough to cause overheating, would detonation be occurring?

M.H. Yount said:

How old is the ?newer? radiator??

And a question for all as I know nothing about these engines - if timing was advanced enough to cause overheating, would detonation be occurring?

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Retarded ignition timing would be more likely to cause an overheat situation, but I don?t think that is OPs issue.

Thx for the reminder - timing significantly off either way can contribute to overheating. Seems like in these situations where none of the usual suspects tests out to be the problem, someone often finds out that the rad has some internal problem - clogged with mineral deposits, corrosion or some such.

M.H. Yount said:

Thx for the reminder - timing significantly off either way can contribute to overheating. Seems like in these situations where none of the usual suspects tests out to be the problem, someone often finds out that the rad has some internal problem - clogged with mineral deposits, corrosion or some such.

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Driving habits can play a big part too. Extended driving in boost can attribute to overheating but that is much less common. Also, being mistimed can cause you to have to push the gas harder which can make you stay in boost. I?ve seen it before.

Mechanical temp gauge.. Maybe the line is picking up radiant heat from turbo and downpipe.

Still do the other suggested checks through, good suggestions. Is the heater core clean and free for coolant flow? Coolant flow from the back of the head is good for keeping things cool.
Maybe the smaller pump pulley on a turbo, higher flow and resulting pressure. Stealthfti wrote some interesting findings about that too.

Check that your radiator isn't plugged up internally. If your radiator is older (original) and the cooling system wasn't properly maintained, its very possible that some of the internal passages are occluded.

Its also very possible that there is a bunch of dirt built up in the fins. This is especially true with the stacked AC condenser / charge cooler / radiator combination. Its all plugged up in between. Pull your charge cooler and wash out the fins on all three. Using some coil cleaner (sold in home depot / lowes) meant for home AC units will help float out all of the gunk packed into the fins.

Make sure that that you don't have a bunch of air bypassing the stack.

The previous poster is correct in saying that the fan (electric or mechanical) shouldn't have any effect at speed.

Assuming all that stuff is clean, you may just need to up grade to a three row radiator. Switching to a lower temperature thermostat may also help. Its also possible that your (new) thermostat and/or water pump is bad.

I should clarify about a radiator fan that is wired backwards. If the fan kicks on at lower speed then the car goes to highway speed while the fan is running the fan will push against the air coming from the front of the car. I've done this myself when swapping out the radiator, including electric fan, on my old 1980 VW Dasher. The engine cooling was fine in town until I tried to go onto the highway, then the engine started to overheat. I stopped the car and the engine cooled. I switched the 2 fan wires and all was good. I had swapped to an older Audi Fox radiator and fan that had different fan wiring plug.

Make sure whether the fan is pushing or is pulling the air through the radiator.

Update

Hey everyone I got my IR thermometer today. First, thanks again to everyone that replied and offered so much good and thoughtful information and advice.

So I went for a short ride and started poked around with the IR with the engine running. Here's what I got: Drivers side top of the plastic riser/side tank was at 180*F, DS middle of plastic at 150*F, DS bottom of plastic at 120*F, passengers side top of riser (and temperature switch) at 90*F, middle of PS plastic at 70*F. The thermostats housing was at 200*F.

I also checked temperatures in the same locations with the e-fan on and off as well as when the thermostat was open and closed. These checks gave similar results with the top DS being hottest and bottom of PS being coldest.

I'm guessing this means a clogged radiator eh?

Thank you all much

moustacio said:

Hey everyone I got my IR thermometer today. First, thanks again to everyone that replied and offered so much good and thoughtful information and advice.

So I went for a short ride and started poked around with the IR with the engine running. Here's what I got: Drivers side top of the plastic riser/side tank was at 180*F, DS middle of plastic at 150*F, DS bottom of plastic at 120*F, passengers side top of riser (and temperature switch) at 90*F, middle of PS plastic at 70*F. The thermostats housing was at 200*F.

I also checked temperatures in the same locations with the e-fan on and off as well as when the thermostat was open and closed. These checks gave similar results with the top DS being hottest and bottom of PS being coldest.

I'm guessing this means a clogged radiator eh?

Thank you all much

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Not necessarily. Could be though..What you just described was a functioning radiator. The coolant temp will drop as it passes through the core. The hottest point of the rad will be when that coolant first enters (driver side top). Idk what your climate is but I can go drive my 240 all around town, get out, stop the mechanical fan with my hand, and touch the PS bottom of the radiator core and it is cold to the touch. It's around 30F here. That just means my radiator is very efficient. In the summer, this will change. It'll have a harder time keeping cool, so the whole core will be warm. Also, the mechanical fan won't be able to be stopped by hand.


Measure again after some highway driving when it's 'overheating'. Another really good place to check is the casting plug ("freeze plug" is what some people call it) on the driver side below the intake. Or really any part of the block for that matter..but casting plug is the most accurate IMO. Anyway, make it 'overheat' again and pull over and check temps. 200F is somewhat normal if it's warm outside, but I'd expect you should be able to hold 180F all day if it's below 60F outside. What temp does the fan come on? I'd kick it on around 195F-200F.

Hey, thank you much.

I should have mentioned that while taking the readings it was around 30*F outside.

iLoveBeingTeaBagged said:

. . . .What you just described was a functioning radiator. . . . .

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What your readings say is that the radiator is working exactly as it should.

My only suggestion is that you will have to check it when the highway driving is causing an issue.

I just took my 93 245 on the highway for 10-15 minutes. Pulled off the highway and immediately took these readings. 36F here. It has an aluminum rad w/ plastic end tanks. Volvo brand I think. Toyota red coolant, and a 180F blue box tstat along with a 1 year old aisin clutch. Here are my readings. Car is NA, but that does not matter, my +T behaves in the same manner.





Take this reading with a grain of salt. These IR thermometers can be weird when reading certain materials, especially anything shiny like polished aluminum.


My guess is that on the highway, you are simply lacking airflow due to the 3 cores, as well as poor shrouding.

moustacio said:

Hi and thank you for your responses.

I was under the assumption that the reading from the block drain location would be lower than if I were able to get a reading from the head. I'll take a look at how I have it routed though, it is a mechanical gauge so you have a point I had not considered. I could maybe put in a light in the dash to indicate whether the e-fan is running or not. That may help in determining if the block temperature is actually reading higher due to the exhaust?

I am using a 2 speed fan and relay from a 940. I mounted the e-fan in the original 740 shroud, using your page as a reference actually. (Thank you by the way, some great info there). I have yet to fill in the gaps with some weatherstripping or the like though. Low speed is being triggered with the radiator sensor, on at 92*C and off at 87*C.

Thank you

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What radiator sensor? The stock one in the end tanks is an overheat switch that the contacts close at about 230F on. Way too hot IMO. That's what the stupid regina cars use.