Hello all,

I just recently got my '77 Cutlass Supreme back on the road after letting her rest for the winter. As part of a Spring-time maintenance, I changed coolant hoses and thermostat for piece of mind, as they hadn't been touched since I bought the car last fall. I replaced the old thermostat with a 195° replacement. Upon taking her out for a drive, I noticed that the engine temperatures were slightly higher than I recall, please see the following pictures and advise, as these temps appear to be a little warmer than what I'm comfortable with. The temperature was barely 70° when I was out cruising. Engine is a stock 350.

This first picture is while maintaining 70mph on the highway, and was much warmer than what I remember her rising to at highway speeds:

vb9GbCL.jpg


This second image is after I coasted down to 60, the temperatures dropped closer to 210 after a few miles:

whBl0E3.jpg

Are these temps typical for highway speeds with an outside temperature around 70? They seem high to me, and I'm not sure if I should swap out the 195 thermostat with something cooler. Also, A replacement oil pressure sender has been ordered, I haven't been able to get a stable reading out of that thing since I started driving her again, it'll either sit between 40 -80, or flatline all the way to the right like in the pictures. Please advise

 

I would take out the 195 and put in a 180 Stant Superstat. Check to make sure you have a good connection for the oil pressure sender, don't use Teflon tape thread sealer.

 

Eric, the 195 thermostat shouldn't cause that problem. I run one too and don't see 230+ temps. Something else is going on there. Is this old gas, and is the timing right?

As you mentioned the oil pressure gauge is way out of whack too. Highway should be somewhere between 40-60, not off the scale. I'm wondering if the temp gauge is also faulty.

 

FYI the thermostat rating is only what temperature it initially opens. See this thread and specifically post number 6 which talks about that some.

 

The rating on a thermostat is where it begins to open. Which means that operating temps will be driven higher. Here is what I found on thermostat ratings vs average fully open temps.


160 thermostat
fully open by 170-175 degrees
170 thermostat
fully open by 180-185 degrees
180 thermostat
fully open by 190-195 degrees
195 thermostat
fully open by 205-210 degrees

 

Thanks for the quick replies guys, I actually drove the Cutlass to work today, and noticed similar temps, but luckily the commute wasn't long enough to get the temps past 210. The gas is fresh, and the timing chain was actually replaced over the winter. I haven't put many miles on since the timing chain was replaced, and I believe was replaced with stock timing. The distributor is new last fall.


The oil pressure sender I purchased was ACDELCO Part #D8034 from RockAuto. I'm not sure what temperature sender to purchase to double check these temps. For the time being I'll stick with the 195 thermostat after reading the previous replies. Trouble is, I'm set to drive this car back north about 60 miles today, and I'm hoping I can line something up to not stress the block any harder than I have to..

 

When they asked about timing they were talking about how many degrees you are running not the timing chain. Is it set to the stock timing mark? How many miles are on the engine? When is the last time the antifreeze was flushed?

 

Ah, sorry, I misunderstood. The engine is set to stock timing, and just turned 125k on the way to work. Antifreeze was flushed within the last 1000 miles, as what originally what started out as a water pump replacement turned into a timing chain replacement as well. I figured since I was that deep I might as well do the timing chain at the same time. Could it perhaps be something with the radiator?

 

Nothing was said about you replacing the water pump before. Did you get the right one? Your flow rate may be less if you didn't.
re: radiator. It wouldn't hurt to take it out and have it hot tanked to clean out any scaling in the core tubes. You might have restricted passages..

 

That's an interesting thought, I purchased this water pump:

O'reilly Auto

I just figured it was the correct pump, although employees are O'Reilly aren't always the most reliable..

 

Did you specify AC?
I just looked at a 77 AC Delco Water pump for a 77 CS with AC and it appears to be different. At the risk of offending you, for 30.00 you get what you pay for.



The AC Delco without AC or HD cooling looks like the one you got

 

I opted out of the AC option, as it has been deleted.

And since I read your disclaimer in your signature, no offense taken

Can you link to the AC Delco water pump you just mentioned?

 

Nevertheless, your engine is spec'd to run with an AC water pump so that IMO is likely the biggest factor. The non AC pump will have less flow.

This link is for the Rockauto website. You'll have to drill down through the Brand, Model, and year. Then select 'cooling system' and 'Water pump' Sorry it's just the way their site works.

Also - if you do go with RA, there are 'stickys' on this site to give you discounts.

 

While I won't discourage you from trying a second temperature sender, if your reading changed after changing the thermostat, I'd blame the thermostat, not the sender. It sounds to me like your new thermostat isn't opening soon enough.

For all you guys who say the thermostat only just cracks open at its rated temperature and doesn't full open until 10-15 degrees higher:

So what?!!! That doesn't mean the engine should run 10 - 15 degrees hotter. As soon as the thermostat cracks open even a little, coolant starts to flow through the radiator -- which keeps the temperature from going any higher. If you radiator has enough cooling capacity (enough coolant, enough fins, enough air flow), then the entire system reaches stasis, with the thermostat opening just enough to maintian a constant temperature. If you suddenly floor it and put more heat into the system, the thermostat will indeed open a little further, at which point that extra heat will be disipated by the radiator and you'll be right back where you started. You might see the temp gauge rise briefly, but long-term the coolant will always stay at the thermostat's rated temperature.

Disclaimer #1: No, I'm not claiming these thermostats are precision devices. Any given thermostat might be off by 5 or 10 degrees. A particular 180-degree 'stat might regulate the system temperature to 175 or 185. But it will hold it constant.

Disclaimer #2: This is all based on your radiator and pump having adequate cooling capacity -- which it did when your car left the factory. Only in the extremest climates and/or extremest usage should you see your engine consistently running hotter than the thermostat.

 

By the way, with both the oil and temperature gauges reading a littl funny, you might want to make sure the gauge cluster has a good solid ground.

 

Thank you everyone for the solid advice.

I ended up making it home yesterday without issue, I had to take a few "pit-stops" along the way to avoid the temps getting too warm. The stops were beneficial, as I swapped out some aged vacuum lines in the parking lot while I let the block cool down. I ordered a replacement AC water pump from a locale store, and should see it come in later today. I'll swap out the water pumps and the oil pressure sender as that arrived in the mail yesterday and report back my findings.

That's a can of worms I've been meaning to get into, but I'll have to dig up some documentation. Unfortunately is appears the PO had his hands in the wiring under the dash, so that may be a whole ordeal of it's own.

 

+1 to all.

If your cooling system is adequate, a 195° thermostat should give you a temperature of 195°.

If it doesn't, there's something wrong.

- Eric

 

+2. Also of note; if your temp going down the freeway with tons of air flow is higher than your around town temps, it points to a lack of cooling capacity. Since your radiator didn't just shrink, that may be another finger pointing at the possibility of reduced flow from your new pump. Some thermostats are higher flowing than others as well.
By the way, we've all heard that engines are heat pumps. A 195 degree 'stat and operating temp is not a bad choice for the engine as long as it is running well, but if you are experiencing any heat related issues like part throttle pinging since the change, you may want to drop to a 180. It sounds like you've checked your timing, but running retarded timing will also generate some additional heat.

 

Does the replacement lower hose have a spring in it ?.

 

The replacement hose did not have a spring in it.

 

Well, that'll do it.

- Eric

 

I'll have to try to fish the old spring out of the old hose, I didn't see a replacement even offered with a spring. I didn't think it was that big of a deal, but now after doing some searching, it appears that is quite important

Under higher RPMs does the engine force the hose to collapse partially?

 

you may be able to observe this collapsing hose phenomenon with the car stationary.

Nice and warm, t'stat open

raise engine RPM and watch lower hose.
If it collapses, GET A VIDEO and share it.

 

Yes and it historically did with the inexpensive hoses of yesteryear without the spring. The lower hose is the suction side of the radiator. Im told that the new school hoses are significantly thicker which is why they no longer include said anti-collapse spring. Couldnt hurt to try the old one if it doesn't crumble upon removal.
All the suggestions here should get you down the road to a cool running engine. My take is once you have the right pump installed the next step is to verify the temp with a known good gauge. You could be fine but the gauge could be lying. If after this the temps still unacceptable have the radiator cleaned or replaced. Do you have a good working clutch fan? It should have one if it was an original AC car. Is the fan shroud present and intact?

 

Just gently grab one end and slowly twist while pulling out.

To install it in the new hose, "screw" it in.

- Eric

 

I've actually got a replacement AC delco water pump new in the box if you decide to swap it. When i get home I'll get the part number for you, but I know if was for a late 70's cutlass.

I'll check if it's the AC application, but I agree, if you're supposed to have the AC style pump, it'd start there. There is a condenser in front of the radiator for the ac right? The larger pump probably help negate the air flow lost to the condenser. Regardless of the compressor being bypassed, etc you probably should have the right water pump.

For a temp quick fix, you could install a small mechanical temp gauge in an unused port in the intake and when you pull over compare the two. I know it's a little redneck, but I did that a couple years back to confirm. Better safe than sorry.

 

I think I'm going to proceed with a swap of the non-AC water pump to a AC water pump tonight. I have seen the higher operating temperatures prior to swapping the hoses and thermostat. I originally decided to swap the hoses and thermostat to see if that would change the behavior at all. I think I'll try to work in the spring in the new hose as well, just for piece of mind.

I will check to see if the lower coolant hose is collapsing, but I think my issue my just be the incorrect water pump being installed. I didn't drive the car again today since temps are supposed to be warmer than yesterday, but I'll take a look again tonight. It may be a long night, but since I want to get her ready for a weekend trip, one late night will be worth it I'll update this thread with any progress.

 

Neither do the replacement hoses for lots of 70's and 80's cars.

I don't think so. The phenom you guys are talking about was for production in the 60's. Since then rad hoses are built differently and don't require the use of a spring to avoid collapse. My 72 has never had a spring in the rad hoses (top or bottom) and they don't collapse when cooling. The hoses on the car are OEM GM.

 

I read that with the cap on and the system pressurized, the lower hose will not collapse.

I recently saw the lower hose collapsing on my car when I flushed the radiator, but that was with the system open (no cap) so it kinda makes sense. I have not checked with the cap on, but maybe that's something I should look at, just to help me sleep better at night.

Or get a spring for the lower hose. Anyone know where to get one?

 

Another way to get a second opinion on your coolant temperature (instead of installing another sender and/or gauge) is to use an infrared gun aimed at the thermostat housing. (Obviously while parked with the hood up, not while driving. ) I don't always trust these guns, because their reading depends in-part on the emmissivity (?) of the surface being measured. But I've seen excellent correlation, at least with the bare aluminum housing on my '70.

 

You don't need the spring in the bottom hose anymore, new hoses are made out of a totally different rubber than original hoses and are much more stiff, I found this out because the last hose I bought didn't have the spring and I called the manufacturer and asked why no spring, I have watched mine and it never changes.

 

Hey guys,

Just a quick update. After work today I pulled the Cutlass into the garage and removed the existing water pump in preparation to replace it with a new AC water pump. Upon pulling the existing water pump, and comparing it to the new AC water pump, I noticed a strange difference between the two pumps:

ReX2rqF.jpg

The pump on the left is the non AC water pump, while the pump on the right is the new AC water pump. Are the differences of the impeller really that drastic between the two different pumps?

By the way, fan shroud is intact, and I do have a fan clutch. Whether or not the clutch is working as intended, I'm not exactly sure.

 

Perhaps, but I'll take the extra 60 seconds to put the old spring into the new hose anyway.



Wow. I am not a water pump authority, but it sure looks like the pump you already have has a much higher capacity.

I don't recall noticing such a big difference between any of the pumps that I have - could the new one be for a 307 instead of a 350?

- Eric

 

Ironically enough, the pump on the left was intended to be placed on a 307 engine, and in a time of need, was placed onto the 350 in the Cutlass to alleviate a leaky water pump.

 

I would be very interested in seeing what someone with personal knowledge about these has to say.

As far as I know, the objective of the water pump is to pump volume, and that new pump does not look capable of pumping as much volume as the older one.

- Eric

 

I remember replacing the WP on my 83 Regency (307) when it crapped out one cold November back in the 90's. The replacement WP was exactly like the one on the right, not the left. And that car never had any issues with cooling - ever. And yes, it was an AC car. I'm guessing the design of the impeller is critical to coolant flow because I thought the same thing as you at first.

I have a replacement WP for my 72 as it's getting HD cooling. It also looks like the pump on the right.

 

Thanks Allan,

Thats puts my mind at ease, I didn't want to button it up last night for fear of running into the same problem again. I'm heading back to the garage after work tonight, and I'll install the pump on the right, and report back my findings.

On an unrelated side note, the replacement oil pressure sender unit I purchased came with some sort of thread sealer, should I beef up that seal with another special sealant, or just trust what's on there?

 

Just trust what's on there.

 

It's a form of pipe dope. Same as on NPT fittings that need to have a good seal and are packaged that way from the manufacturer. It should have no effect on the ground you need when it threads into the block.

 

Alright sounds good. I can't wait to get this thing back up and on the road again