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Running Hot on Freeway

Thank you much for doing that and for the excellent pictures, I much appreciate it.

I'm using a Saab temperature switch made by Vernet, part number 9526518

I will take some readings after a freeway run to work on Monday. I'll be away from the car for a few days. However, with the cool weather I don't see the gauge go above 180*F or so.

To respond to some older posts: I did verify the fan is pulling air into the engine bay. I plan on buying some of the cleaning chemicals to get the oustides of the IC, condenser, and radiator coils. Will also start on closing up the areas between the IC, radiator, a/c to get more air passing through the radiator. I use an 82*C thermostat in the summer, an 87*C is in there now.

Also, I couldn't get an IR reading on the temp sensor line coming from the block but the way I routed it doesn't appear to be being affected by the exhaust pipe. It runs basically out of the drain petcock, down, and then toward the drivers side. The oil filter read 140*F. I could certainly be wrong about this and will wrap the sensor to gauge line on the exhaust side with some aluminum foil.

I will keep going with the other suggestions made and my list above and let y'all know what I find. I'm flying out of town tommorow but I should have some kind of update by early next week.

Thank you guys.
 
Hey,

I'm at around 5,500' and drive to around 7,500' regularly. I do drive the car up into the mountains and the highest its been was around 12,000' or so. Temperature is usually good on the more backroad type mountain roads but I've only had the block temp gauge in for under a year.

Thanks again
 
Hello,

I took a few readings after exiting the highway and got the highly similar results to what is posted above. It was around 60*F here and the block temp gauge I have showed a stable 180*F on the freeway. I will have to wait until it gets hotter outside to get some readings while the engine is running too warm on the freeway.

Hopefully sorting some other things out will stop the issue by then. I'll post back in the summer with what I find.

Thank you much
 
I'm guessing this means a clogged radiator eh?

Thank you all much

Based upon your 90*F delta on the surface of the radiator (and really you want fluid temps; I'd shoot the hoses at entry/exit and ignore the plastic temps), in my mind it points to little to now flow.

Remove it, gravity test, and you'll have your answer I believe. There must be pressure drop across the radiator tubes, but the suction side of your radiator is probably lower than spec and you might even be flashing to steam if you go low enough (all depends on phase change point for your coolant AND actual pressure on the suction side).
 
Actually, I've never heard of a block temperature sensor before. Thinking they're usually mounted on the head.
 
Well just to throw my 2 cents in:

Typically in the past when I've had hot at freeway speeds, it turned out to be a flow problem, and in my case a failing/ed water pump.
Not sure if this helps, but that's been my experience.
 
Hey everyone,

It's getting warmer here so I thought I would follow up with what's going on. Not sure if my issue is solved but so far so good with my block water temperature gauge being pretty solid between 190-195*F even with a/c running close to 90*F ambient.

Since posting I have done the following:
-Cleaned/sprayed the radiator, intercooler, a/c condenser, and air cooled oil cooler again
-filled in some of the gaps to get better air flow to the radiator
-installed Saab upper radiator tee with 92*C temp switch to trigger low fan speed
-heater hoses and heater control valve

Something that I don't think came up is the possibility of a radiator hose collapsing on a hot motor with higher freeway rpm's. Am I correct to assume that the lower radiator hose to the water pump would be the one that could collapse?

Thanks again everyone for the excellent ideas and suggestions and I'll follow up again either way after summer has past. And lummert, the block temperature sensor I have is an aftermarket mechanical sensor threaded into the drain petcock below the exhaust manifold on cylinder 4. I still have the cylinder head one installed but don't know how to bypass the compensation, it just stays in the middle after warming up to temp.
 
A laser thermometer might add additional bit of information. My radiator was blocked about half way up on the input tank so that it only was about half effective.
 
Something that I don't think came up is the possibility of a radiator hose collapsing on a hot motor with higher freeway rpm's. Am I correct to assume that the lower radiator hose to the water pump would be the one that could collapse?

.

Bottom hose is indeed the "suction hose" ; old school Detroit iron used a spring inside these hoses to prevent them collapsing. Factory Ovlov hose is just reinforced more to prevent the collapse. I'd recommend the OE hose on the bottom just to be certain......
 
How old is the waterpump?
How old is the radiator? What kind of radiator?

rPQj0.jpg
 
Hey folks,

Thought I would give an update since its been pretty hot here. Also believe I might have come to a conclusion about the high readings as mocambique-amazone suggested at the beginning of this thread. Also, thank you much everyone for the great ideas and help.

I may change the lower rad hose for good measure and in the meantime I have wrapped it in a few place to hopefully keep it from collapsing with duck brand silicone wrap/tape. New 82*C Thermostat, Hepu water pump, Nissens radiator are all in use for under 10K miles.

**I'm thinking that the mechanical temp sensor in the block drain petcock (exhaust side towards the firewall) is giving higher than actual temperature readings on the freeway** Thank you mocambique-amazone for pointing this out right away and sorry for not taking your advice.

Now for the novel:

-I recently had to replace my AC condenser so I made some sheet metal guides to better direct the airflow to the radiator. Also, fit some sheet metal on my 940 e-fan and stock 740 shroud where there was gaps previously. The latter made a large improvement on pulling air through the rad. As previously posted, I also cleaned the exterior of all the coils behind the grill and filled in some gaps above and below the coils.

-Today, while climbing 1000' for 30 miles in 90*F weather and AC on the block temp sensor was showing up to 205*F. As testpoint and ihatevulvapeople suggested I pulled over to the side of the exit ramp to obtain temperature readings. Thermostat housing was 192*F, upper rad hose and drivers side radiator plastic was 188*F, passenger side rad plastic at top was 166*F, mid PS
At 154*F. And, stock temp gauge has never moved from its 12 o'clock position.

I never wrapped the mechanical sensor with anything to act as a heat shield so I am going to give that a go and see if I notice a change. Strange that this only happens at highway speed but likely logical as my car does have to see around 5psi for extended time while gaining elevation. Also strange to me is that running the heater at full blast and/or running the e-fan at high speed will decrease the temperature I see on the gauge by 5-10*F relatively quickly.

I'll update again when I'm certain but this seems to be the cause of all my anxiety and wasted time for everyone reading and helping me along the way.

Thanks everyone
 
Hey,

It wasn't too hot during my trip but the car made it just over 1000 miles across country and I never saw the temperature gauge reading from the block drain petcock location get over 190*F. As others have suggested the cause for all of my concern is the positioning of the mechanical sensor.

Seems I enjoy torturing myself with made up problems. Anyway, I thought I would update this again and let y'all know this 740 is still kicking
 
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