83 Burb converted to 396 Big Block

[Stoney_06]

Hey Guys,

Forum lurker here. I got a 83 Burb that used to have the diesel in it. The guy I bought it from dropped a 396 Big Block out of a 68 Chevelle into about 5 years ago. I've had the rig for about 7 months and keep running into little mechancal gremlins on the engine conversion. The worst so far being the orignal 700R4 losing 2nd gear from the BB conversion. But that is getting fixed with a manual 4 speed here in the next couple months.

My largest concern right now is the engine temprature. When I bought the rig it was constantly reading an engine temp of around 220 to 230 at the gauge. I ended up draining the coolant, installing a block heater and a new thermostat, and putting in some good 50/50. I ran the rig for another couple weeks but the temprature showed the same readings and behavior. Additionally the heads don't appear to be running hot (no smoke or anything. Can touch with a bare hand.) I can grab the upper and lower coolant hoses with my bare hands. I might be hearing a occasional ping sound but I haven't been able to tell if that is actually a heat ping or from another mechanical issue. That being said I believe the thermostat is good or at least not a variable to address.

Next I replaced the temprature sending unit. I have an immediate change in cold start idle. It appears to be running smoother. Is the sending unit related to any other operations such as the electronic choke? Also, my temprature gauge is reading well past the 240 degrees now. I also believe I might have heard the ping again this morning but could not confirm because it wasn't consistent. When I popped the hood I was still able to grab the coolant lines. No smoking. Smooth idle. What the heck?!

My current plan of action is to place an stick thermometer in the coolant line where the it connects to the thermostat. I was also going to use a laser thermometer to check the radiator for plugs and hot spots on the engine.

Should I consider a gauge replacment next? If so what is the recommend reliable budget gauge? Are there other things or parts to test that may be going bad? Is there a possible connection or issue that is a result of the engine conversion that I will need to consider adapting over? I love the engine in Bertha but I'm scared to burn it up.


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[1987 GMC Jimmy]

I would purchase a non contact thermometer and point it at a bare spot on the side of the cylinder head once it all warms up. If you get the same results, I'd consider doing a coolant flush and a new water pump. If you don't get the same results, I'd try replacing the coolant temp sending unit first.

 

[Stoney_06]

I would purchase a non contact thermometer and point it at a bare spot on the side of the cylinder head once it all warms up. If you get the same results, I'd consider doing a coolant flush and a new water pump. If you don't get the same results, I'd try replacing the coolant temp sending unit first.

Dang! I hadn't even considered the water pump. I'll have a non contact thermometer by tonight. I've just replaced the sending unit which caused the smoother idol but drastic gauge reading change. You think it my be a bad unit straight out of the box? Is there a particular sending unit style to avoid I should avoid as such? Is there a possiblity that the diesel gauge is calibrated differently than the gas sending unit?

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[1987 GMC Jimmy]

Dang! I hadn't even considered the water pump. I'll have a non contact thermometer by tonight. I've just replaced the sending unit which caused the smoother idol but drastic gauge reading change. You think it my be a bad unit straight out of the box? Is there a particular sending unit style to avoid I should avoid as such? Is there a possiblity that the diesel gauge is calibrated differently than the gas sending unit?

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The thing with water pumps, especially old ones, is that even if they don't fail visibly with bearing failure and water leakage out of the weep holes, the impeller can erode and reduce efficiency and effectiveness over time. You've replaced the thermostat, which is important. Since you're going through everything, I'd just inspect for leaks of any sort whether they be under the hood or on the passenger side floorboard (heater core). Any leak is a detriment to operating temperature, however small it is. As far as the sending unit goes, there are two types, but the differences in their resistance parameters have to do with dummy light versus gauge rather than gasoline versus diesel. My consensus on it from what I've both seen and read is that a bladed style sending unit is affiliated with the dummy light, and a "ball style" sending unit is affiliated with the gauge. I put a bladed style sending unit on my Jimmy back almost two years ago, and it read about 235 at operating temp when it was actually 195. I was checking out a 454 Suburban a while back that had gauges, and I noticed that it had the ball style sending unit. I don't know if that's universal, though. Which kind is on it now? And the coolant temperature sending unit doesn't have any affect on vehicle operation so maybe you tweaked something else? The coolant temperature sensor on a TBI, TPI, MPFI, etc. does, but it's connected to the ECM to help tabulate fuel-air mixture appropriate for a certain engine temperature.

 

[1987 GMC Jimmy]

I just looked on RockAuto, and they show the sending unit for both the gauge and dummy light as being bladed, with the gauge sender having a slightly longer, barbed blade and the light sender having a shorter, smooth blade. I looked on Autozone, and they show this ball style sender being gauge compatible, as well. I'm glad I disclaimed consensus rather than fact because all I can go by is what I've seen for myself and read of others' experience. If it were me, I'd just exchange them for a different one until I got the most accurate readout I could. Unless you want to order one directly from RockAuto that is claimed to be the correct one. Oh, and this is what I meant by a ball style sender.

 

[Stoney_06]

The thing with water pumps, especially old ones, is that even if they don't fail visibly with bearing failure and water leakage out of the weep holes, the impeller can erode and reduce efficiency and effectiveness over time. You've replaced the thermostat, which is important. Since you're going through everything, I'd just inspect for leaks of any sort whether they be under the hood or on the passenger side floorboard (heater core). Any leak is a detriment to operating temperature, however small it is. As far as the sending unit goes, there are two types, but the differences in their resistance parameters have to do with dummy light versus gauge rather than gasoline versus diesel. My consensus on it from what I've both seen and read is that a bladed style sending unit is affiliated with the dummy light, and a "ball style" sending unit is affiliated with the gauge. I put a bladed style sending unit on my Jimmy back almost two years ago, and it read about 235 at operating temp when it was actually 195. I was checking out a 454 Suburban a while back that had gauges, and I noticed that it had the ball style sending unit. I don't know if that's universal, though. Which kind is on it now? And the coolant temperature sending unit doesn't have any affect on vehicle operation so maybe you tweaked something else? The coolant temperature sensor on a TBI, TPI, MPFI, etc. does, but it's connected to the ECM to help tabulate fuel-air mixture appropriate for a certain engine temperature.

Gotcha! I do have the ball style sending unit. I'm going to go and make sure my sending unit wire is not damaged and that the connector is making solid contact as well. I made sure to install the new unit with no tape so as to ensure a good ground. I checked it for leaks and it was okay. I will go through and double check other areas for leaks. Impeller erosion is another thing I hadn't thought of that makes sense too. I don't think the prior owner ever replaced it. I will go through and check all of his reciepts and do the temprature test as you suggest. I love and hate these puzzles. I appreciate the advice by the way!

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[1987 GMC Jimmy]

No problem! I wish I could give you a more straightforward answer on the senders, and maybe someone else could, but I'm just going by what I've seen. Maybe the safest thing to do is go online and get one that specifies what it's for if your tests don't show any cooling problems. They're only like four dollars plus whatever shipping they add minus the 5% GMSB discount. Good call on the wiring, too. I don't know about you, but I've had multiple skirmishes with rodents making chew toys out of my underhood wires. But yeah, let us know what you find out with the thermometer tonight.

 

[Stoney_06]

No problem! I wish I could give you a more straightforward answer on the senders, and maybe someone else could, but I'm just going by what I've seen. Maybe the safest thing to do is go online and get one that specifies what it's for if your tests don't show any cooling problems. They're only like four dollars plus whatever shipping they add minus the 5% GMSB discount. Good call on the wiring, too. I don't know about you, but I've had multiple skirmishes with rodents making chew toys out of my underhood wires. But yeah, let us know what you find out with the thermometer tonight.

Partial success! Using the laser thermometer I warmed the engine up. On the heads I was getting around 178. On the temperature sending unit I was getting around 210 on average. I did have a spike of 236 but I might have wavered to the exhaust manifold.

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On the thermostat I had a high of 186 and a low of 172. Pictured are the averages. I was able to watch the temperature cycle as the thermostat opened and closed.

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I didn't get a picture of head temperature but it was averaging 178. The entire time my dash showed this.

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So, I'm thinking it's safe to say there is a there is an issue between the sending unit and the dash. I did notice a spot that may have a splice I will investigate that tomorrow.

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[1987 GMC Jimmy]

Is the sender threaded into the driver side cylinder head near the spark plugs?

 

[bucket]

If it was suspected to be reading high, and now it's pegged on hot after changing the sending unit, it could very well be a bad wire or poor connection. Moving the wire while changing the sender could have made the problem worse.

...Or I suppose it could just be a defective sender along with a gauge that reads a little hotter than it should.

 

[Stoney_06]

Is the sender threaded into the driver side cylinder head near the spark plugs?

Yes. I'm thinking about relocating it onto the intake manifold near the thermostat.

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[Stoney_06]

If it was suspected to be reading high, and now it's pegged on hot after changing the sending unit, it could very well be a bad wire or poor connection. Moving the wire while changing the sender could have made the problem worse.

...Or I suppose it could just be a defective sender along with a gauge that reads a little hotter than it should.

I'll see if I can get into that wire before I lose light tomorrow.

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[1987 GMC Jimmy]

The cylinder head is the best spot in my opinion. That gives you your truest operating temperature, I think.

 

[Stoney_06]

The cylinder head is the best spot in my opinion. That gives you your truest operating temperature, I think.

Duly noted! [emoji2]

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[74 Shortbed]

The cylinder head is the best spot in my opinion. That gives you your truest operating temperature, I think.

That is correct..