Hey guys, I have been having a problem with my blazer running hot when I go up hills for a bit now and I thought it was because air was getting in the system from my bypass hose leaking. However, I have just fixed that leak and it still gets hot while going up hills, and a new thing I have noticed since fixing the bypass hose is the coolant temp will rise significantly after I shut off the engine, today it was up almost at the 3/4 mark a bit after turning the engine off. I have a new water pump and rad last winter, new head gasket a year ago, new thermostat 2 months ago, fresh coolant in the system 3 days ago, rad and ac condenser are clean (excluding a few bugs), my fan is working as intended. The only thing I have not replaced is the rad cap. I have checked all the hoses and water pump weep holes for leaks and found nothing. I'm thinking about replacing the rad cap but want some opinions first.

This may be my engineer kicking in, but I'm thinking after the engine is off there is no more heat source so if the coolant temp rises it really just reaches equilibrium temp with the engine. If it rises to 3/4 on the gauge after turning it off, then that would mean my engine might be running a little hot before I turned it off to allow the coolant to heat up more than normal. Now it's time to drop some numbers, when I'm driving around the city even with the A/C on the temp will stay about 92-96 degrees. The problems arise when the hill comes, then about 2-3 minutes into a hill climb I will see the temp start climbing (it climbs by 2 deg increments on my tablet!), when I'm at the top of the hill it will be at 101-103 degrees. When I have been offroading and doing a big hill climb I have almost had to shut the show down because it gets too hot (about 107 degrees). Then when I reach the top the fan will be screaming and the temps will gradually drop back down. I have a 1400km trip coming up in 2 weeks and I would be crushed to not be able to drive my beast (and have to beg my mom to drive her ford lol) so this has risen to #1 on my to-do list. Let me know what you guys think!

 

Try parking it with nose up on a serious hill and let it cool down. See if you can very slowly get more water in it.

I really don't think 103C is too hot. Mine runs at 210/215F at times in hot weather.

 

Are you losing water? That could be a problem.
After the engine heats up does the reservoir level rise and increase in temperature? If it doesn't, yes, try a new rad cap.

 

Thanks guys, I'm used to my temp gauge being in the mid 90's at all times (96-98 max) so something is definitely going on here especially with it getting so hot after shut down. It has been some of the hottest days of the year lately but that shouldn't make a difference in my mind, the cooling system is built with the ability to cool more than needed, and what I see when going up hills is insufficient cooling! I have noticed the coolant level in the res go down a bit since filling it up, maybe from letting out air. I jacked it up today and tried to get more air out, I may have got a little but not much. I decided to get a new rad cap today, being the only part I haven't replaced yet and everything else seems in good working order, for $9 I couldn't go wrong with a new one lol. I will update how the drive to work goes tomorrow morning.

 

They all swelter with heat after shutdown on hot days. It's not so noticeable on cooler days. And you're not sucking air in through any of your coolant hoses, they are only capable of leaking water. It sounds to me like you're overly concerned about normal operation on hot days.

 

So after driving it around today and taking it on the highway for a bit, I think there is air in the system as you said Les. The reason is I can hear a rattling or gurgling from behind the dash right where the heater core is when I'm idling, it seems to go away when I'm on the gas. Also when I'm really on the gas for periods of time on the flat I don't notice the temp rise at all, today it stayed at a cool 90-93 degrees around town and on the highway. I think this hill I go up every day to get home can't be making the engine work much harder than it is when I'm on the highway, but it runs hotter every time no matter what speed I'm going.

I'm going to get one of those no-spill funnels tomorrow and try my luck with at least making the gurgling sound go away.

 

I had th same issue going on with my 99 in this Texas heat stroke.. I mean streak. I went a step above the no spill funnel and tried one of the $20 coolant burping systems off Amazon and that finally got most, if not all of the air out of the system. Neat little setup that seals a large funnel to a variety of different style radiator/fill caps that gives you decently tall sides so the coolant doesn't splash out when the big bubbles start gurgling out. Just make sure and remember to turn on the heater so it purges the heater core at the same time. I changed out the thermostat twice, hoses once, then the cap (which 'found' a new leak in the radiator after pressurized), and then the radiator itself. It used to stay around 185F in the much cooler Pacific Northwest and now hits around 200 F but in 108 F air Temps I'll take it as a win. The factory thermostat is 198 F (close enough to your 98 C) so that's where it's 'supposed' to open up which didn't give 'me' enough headroom over here in this dry Texas heat so I dropped to a 170 F thermostat. If it ever gets cold here, I'll unpack one of my coats.

 

Next time I change out the coolant, I'll have to get one of those funnels. My substitute was parking my truck on part of my driveway with a bit of an incline.

 

Glad to hear I'm not the only one with this problem. So I wanted to come to update this after driving over 2000km last weekend over the biggest mountain passes around me (Coquihalla pass in particular with a 1244m summit, it's a big climb!). So starting the drive out there I was watching the coolant temp on my tablet like a hawk, and right from the start it would move between 87-93 degrees, and it wouldn't be when I was on the throttle it would jump up either, sometimes going up hills it would be 88 or 90 then going downhill it would get to 93. It was a champ the whole way there, over the coq pass it stayed at 90-91 degrees for the whole hill climb! This is what it should be like, a stable cooling system that can accept high load and keep the same temp for a long period of time. It finished the drive there like this and never had any problems putting it around the city for the few days I was there.

On the way back I noticed she was running a little hotter, seeing temps in the 80s was lucky now as they were staying more 91-94. Going up the coq pass on the way back I saw 97 degrees right when I was passing the summit! It continued to run a few degrees hotter hovering around the low 90s instead of high 80s for the rest of the trip. I was also seeing the temp rise when I would go up hills here as well, when just going along it would be around 91, uphill go up to 94, then downhill it would cool off and sometimes get into the high 80s. I'm going to have a look at my thermostat here, even though it's only a few months old, I feel these problems may have come shortly after putting it in.

My final remarks here, it seems a lot of people have trouble with these engines running a little hot. It seems my engine will handle whatever I throw at it and still keep a reasonable temperature, I'm going to confirm the original problem was probably due to air in the cooling system. When I go off-roading next and head up the big hill I'll keep an eye on the temps again, but I think everything is working just fine for now. I may put in an upgraded rad like Christine did in the future, but that's for another conversation.